different aspect in an age which we term Malayan or Indo-Malayan, since
the bulk of the plants are thence derived. The earliest age of the
Coniferæ was, as we have seen in the previous chapter, restricted to the
region of the Western Pacific. The following age of the Compositæ and
the Lobeliaceæ was concerned with the regions of Tahiti and Hawaii. Now,
however, in the Malayan era, the whole of the tropical Pacific is
concerned. Yet, although we shall still regard, for purposes of
convenience, the groups of Fiji, Tahiti, and Hawaii as the three foci of
plant-distribution, it will soon become apparent that in future there
will be in reality only two regions to deal with, the Hawaiian in the
North Pacific, and the whole region of the South Pacific extending from
Fiji to Tahiti and as far east as the islands stretch. It will be also
seen that in making our comparison we shall sometimes have to regard
each of the principal Hawaiian islands as the equivalent as a
plant-centre of an entire archipelago of the South Pacific.
The genera that are here selected to represent this epoch of wide
dispersion are very characteristic of the floras of the Pacific islands.
Genera like Pittosporum, Gardenia, Psychotria, Cyrtandra, Freycinetia,
and others one meets with everywhere in the larger islands, and it
should be observed that they are predominantly Old World, and more
especially Malayan, in their origin, not a single purely American genus,
unless we except the decadent genus of fan-palms, Pritchardia, occurring
among them. Here we notice [what we shall see is especially typical of
the era of the non-endemic genera, excepting those of the lofty uplands
of Hawaii] that the frugivorous bird has been the principal agent in
dispersing the plants, quite two-thirds of the total genera possessing
drupes or berries that would attract such birds. The transport of seeds
or seedvessels in birds’ plumage, which was a conspicuous feature in the
case of the mountain-flora of Hawaii, is not a feature of this age of
wide dispersal of tropical plants over the Pacific.
The genera selected to represent this age are given in the following
table. Those on which my observations directly bear, or in which I was
particularly interested when in the Pacific, will be discussed in detail
from the standpoint of dispersal; whilst only a brief reference will be
made to a few of the others, not, however, from lack of materials at my
disposal, but merely to keep this volume within moderate bounds.
_Genera selected to represent the Age of Wide-dispersal of Indo-Malayan
or Malayan Plants over the Pacific, and possessing in Hawaii only
Endemic Species._—Most of the genera of this age are exclusively from
the tropics of the Old World, whilst those found on both sides of the
Pacific can be shown in most cases to have been derived from the same
source, and only very few, like Pritchardia, can be traced to America.
Pittosporum (Pittosporeæ).
Sapindus (Sapindaceæ).
Reynoldsia or Trevesia (Araliaceæ)
Gardenia (Rubiaceæ).
Psychotria (Rubiaceæ).
Cyrtandra (Gesneraceæ).
Phyllanthus (Euphorbiaceæ).
Pritchardia (Palmaceæ).
Freycinetia (Pandanaceæ).
PITTOSPORUM (Pittosporeæ).
This genus, which contains nearly a hundred species, usually of small
trees, is widely spread in the warmer regions of Africa, Asia,
Australia, and New Zealand. It is also especially a genus of oceanic
islands, occurring not only in those of the Pacific but also in Madeira
and Teneriffe in the Atlantic.
Though found in most of the larger Pacific groups, it has apparently
never been recorded from Samoa. From Hawaii ten species are known, all
peculiar to that group. About half a dozen have been described from
Fiji, of which three at least have been observed outside the group in
the neighbouring Tongan Islands. Rarotonga possesses a peculiar species
which, however, is so near to two other Fijian and Tongan species that,
according to Cheeseman’s memoir, they may have to be subsequently
united. Tahiti is credited by Drake del Castillo with a solitary species
widely distributed in the Old World, whilst in the _Index Kewensis_ a
peculiar species is assigned to it. They form small trees of the wooded
mountain-slopes of Fiji; whilst in Hawaii, beside occurring in the lower
forests, they may extend to altitudes of between 5,000 and 7,000 feet.
In the connection that more or less exists between the species of the
South Pacific archipelagoes, and in the endemic character of all the
Hawaiian species, we see the principle exemplified that there are two
regions of distribution in the islands of the tropical Pacific—the
Hawaiian region and the South Pacific region.
Before their dehiscence, the wrinkled, woody capsules would seem very
unlikely to attract birds; but the observer on handling an opening
fruit, with its orange or brightly coloured lining and displaying black
or dark-purple seeds immersed in a semi-liquid pulp, would form a
different idea of the plant’s capacity for this mode of dispersal. The
mature dehiscing fruits are very conspicuous on the tree; and the seeds
covered with the “sticky” material of the pulp might possibly adhere to
birds pecking at the fruit. But this would only aid in local dispersion,
since the weight and size of the seeds, 5 to 8 millimetres (2/10 to 3/10
inch), would unfit them for this mode of transport across an ocean. They
are, however, sufficiently protected by their hard tests to be able to
pass unharmed through a bird’s intestinal canal.
Yet the distribution of the species of Pittosporum in the Pacific would
show that their dispersal is more a matter of the past than of the
present. Out of the ten peculiar Hawaiian species, Hillebrand designates
none as generally distributed over the group. But it is evident that,
though it is on the point of breaking off, some sort of connection still
exists in the South Pacific between the Tongan and Fijian species, and
until recently between the species of those two groups and of Rarotonga.
REYNOLDSIA (Araliaceæ).
The Polynesian genus of Reynoldsia, originally established by Gray, is
merged by Hooker and Bentham into the Malayan genus Trevesia, a step
that brings the Pacific plants into line with many other of the plants
hailing originally from the Old World. The significant fact in the
distribution of this genus of small trees in the Pacific is that its
dispersal over the ocean has ceased long ago, since the three species
here occurring are restricted each to a particular group, namely, to
Hawaii, Tahiti, and Samoa. Yet the inter-island dispersal still
continues in the Hawaiian Group, the species characteristic of that
archipelago being found in all the islands.
Reynoldsia sandwicensis came frequently under my notice in Hawaii, and
the fairly fleshy drupes, about one-third of an inch, or 8 millimetres,
in size, with their crustaceous pyrenes appeared to me well fitted for
assisting the dispersal of the plant by frugivorous birds. Yet here the
same question arises that presents itself with so many other Hawaiian
plants, and that is, How has it happened that the birds have continued
to disperse the species over the scattered islands of this group long
after they ceased to transport fresh seeds from the outside world? The
answer is an obvious one. The birds that originally brought the seeds of
the parent species from some distant region came at last to remain
permanently in the Hawaiian Group, and not only the plant but probably
also the bird has since undergone specific differentiation. This link
between bird and plant in the floral history of a group of Pacific
islands is the common theme of the story of most of the endemic species
of plants in this region of the globe.
GARDENIA (Rubiaceæ).
This genus, comprising about a hundred known species, is spread over
tropical Africa, Asia, and America, and over all the groups of the
tropical Pacific. On account of their handsome, white, scented flowers
these shrubs are much appreciated by the Pacific islanders, who employ
the flowers for personal decoration. Some ten species have been
described from the groups of the open Pacific, all of which, with the
exception of Gardenia tahitensis, which ranges the South Pacific from
Fiji to the Marquesas and Tahiti, are seemingly peculiar to the
different archipelagoes. Thus there are some six species endemic to
Fiji, one to Samoa, and two to Hawaii.
The Hawaiian Islands are, however, quite isolated in this respect, since
the group possesses only peculiar species; whilst a solitary species
keeps up the connection between the groups on the south side of the
equator. The Gardenias thus tell the same story of complete isolation in
Hawaii, and of partial isolation in the archipelagoes of the South
Pacific that is repeated by many other Pacific genera. Yet in Hawaii
there has subsequently been some inter-island dispersal, since the
species are not restricted each to a single island, but are found on two
or three islands. The significance of the relation of the Hawaiian
Gardenias to those of the combined Fijian and Tahitian areas consists in
regarding the two regions, the Hawaiian and the South Pacific, as of
equivalent value, and each large Hawaiian island as equivalent to one of
the southern archipelagoes.
_The Station of the Pacific Gardenias._—Although they may occur in the
forests, the Gardenias of the Pacific are most characteristic of dry,
thinly vegetated localities, and they have an inclination for the
vicinity of the coast. In the Tahitian Group, as we learn from the
writings of Nadeaud and Drake del Castillo, Gardenia tahitensis thrives
much better on coral islands than on volcanic soils, and, in fact,
rarely quits the “_région madréporique_.” It is sometimes planted in
Polynesia near the houses, and both Nadeaud in Tahiti and Cheeseman in
Rarotonga consider that it was probably introduced into those islands
before the arrival of Europeans. The aborigines may have assisted in the
dispersal of the genus to a small extent, but from the presence of
peculiar species in Hawaii, Samoa, and Fiji it is apparent that the
genus is truly indigenous in the Pacific islands, and long antedated
their occupation by man. This is also evident from the station of the
species in Hawaii, Samoa, and Fiji. In Hawaii they may be found on the
dry forehills in the vicinity of the sea-border. In Samoa, as Reinecke
informs us, Gardenia tahitensis is very widely spread in the
mountain-forests, whilst the endemic species is found thriving in
inundated coast districts. In Fiji I found the Gardenias to be
especially characteristic (as is also pointed out by Horne) of the dry
districts on the leeward side of the larger islands. On the rolling
“talasinga” or “sun-burnt” plains of the north side of Vanua Levu they
thrive in numbers; and here their leaf-buds and the extremities of the
young shoots are often tipped or covered over with an amber-like
gum-resin which the natives chew.
_The Mode of Dispersal of the Pacific Gardenias._—The fruits of this
genus are usually described as indehiscent. If this were true of Pacific
plants it would be very difficult to explain the dispersal of hard, dry
fruits an inch in size over this region. In the case of two or three
Fijian species, I paid especial attention to this point by examining the
plants in fruit. As exhibited in Fiji the fruits are globose, hard, and
almost stony, with persistent adherent calyx, the seeds lying
horizontally in a pulp at first firm and subsequently softening as the
fruit matures. The fruits are not as a rule to be observed opening on
the plant; but they are to be seen dehiscing septicidally on the ground
beneath, the detached woody valves being scattered around. If one of the
fruits gathered from the plant is kept soaking in water for some time it
will begin to dehisce; and this is probably what occurs with fallen
fruits in wet weather. Dr. Hillebrand regards the fruits of the Hawaiian
species as indehiscent. I did not myself examine them, but it is not
improbable that, like those in Fiji, they dehisce whilst lying soaking
on the ground.
Judged merely from the dispersal standpoint, the fruits of the Fijian
Gardenias come near to those of Pittosporum, and both can be in a sense
described as baccate capsules. The flat, crustaceous seeds of Gardenia,
which are usually two or three millimetres in size, are also well fitted
for passing without injury through the digestive canal of a bird. It is
likely that the two genera have been dispersed in the Pacific by the
same kind of birds; and it should be remarked that their distribution is
somewhat similar, both belonging to the warm regions of the Old World.
It might at first appear from some experiments of mine made in Fiji that
the dried fruits of Gardenia could be dispersed over oceans by the
currents. This receives some support by the preference for a littoral
station sometimes shown by G. tahitensis in Tahiti, and by the
occurrence of G. zanguebarica in the East African strand-flora
(Schimper’s _Ind. Mal. Strand-flora_, p. 131). It will, however, be
pointed out that currents could only have aided the dispersal of the
genus to a limited extent. The fresh fruits of Fijian species, with or
without the adherent calyx, have little or no buoyancy, and the seeds
sink even after drying for months. But it was ascertained that fruits
which had been kept for three months floated after four or five weeks’
immersion in sea-water. On examination, however, it was found that the
valves gaped a little, being only held in apposition by the adherent
calyx, and that water had penetrated into the interior, the pulp being
in a state of decay. The fruits were, in fact, kept afloat in the latter
part of the experiment partly by the investing calyx and partly by gas
generated in the decomposing pulp. Ultimately they broke down altogether
and the seeds sank. In the “rough-and-tumble” of ocean-transport this
could scarcely be deemed an effective means of dispersal; and in the
open sea a fortnight would probably represent the limit of the floating
power. It is to the agency that has distributed the genus Pittosporum
over the Pacific that we must look for the explanation of the dispersal
of Gardenia over the same ocean, namely, to birds.
PSYCHOTRIA (Rubiaceæ).
We find in this large genus of the Old and New Worlds a typical example
of the plants with fleshy drupes containing hard pyrenes that represent,
from the standpoint of dispersal, a common Rubiaceous type of plant in
the tropical Pacific. Such plants, of which those of Coprosma and
Nertera may be cited as other instances, are in a generic sense always
widely distributed in these islands. They are eminently suited for
dispersal by frugivorous birds; and it is a matter for surprise,
therefore, that in a genus like Nertera the solitary Pacific species has
such a wide range, whilst with Psychotria and Coprosma the numerous
species are usually restricted to particular groups. Genera doubtless
have their periods of development and decadence in the Pacific, and
probably Nertera is to be regarded as a decadent genus. These Rubiaceous
genera, however, appear to be well fitted for the investigation of the
centres of dispersal of particular genera and of their relative age.
The Psychotrias in these islands are typically shrubs of the shady
woods, and they may be seen thriving best where the forest-growth is
rank and the humidity greatest. Their bright red ovoid drupes, which
range from eight to twenty-five millimetres in length (1/3 to 1 inch),
would readily attract birds, and their crustaceous pyrenes, that vary
between five and eight millimetres (1/5 to 1/3 inch) in length, would
pass unharmed through a bird’s digestive canal. That fruit pigeons can
distribute their seeds over the Pacific has been long established, and
Mr. Hemsley includes Psychotria amongst those genera which, from the
collections of fruits and seeds found in the crops of fruit-pigeons,
made by Professor Moseley, myself, and others, in the groups of the
Western Pacific, are “known to be dispersed by birds in Polynesia”
(_Introd. Bot. Chall. Exped._, p. 45). It is thus hardly necessary to
point out that neither the entire fruits nor the separate pyrenes could
be transported by the currents, my observations showing that in both
cases they sink at once or in a day or two.
Psychotria, however, is an enormous genus including, according to the
_Index Kewensis_, some 600 or 700 described species, distributed in the
tropics all over the world, and also extending into subtropical regions,
the greatest concentration being in America. It is described in the
_Genera Plantarum_ as a polymorphous genus distinguished by no certain
characters from some other genera of the tribe of the Rubiaceæ to which
it has given its name. We have here a genus that has overrun the
tropical regions of the world, probably originating in America; and we
may contrast it with the relatively small Rubiaceous genus of Coprosma
(with its three score of species, and quite comparable with it from the
standpoint of capacity for dispersal), that, having its birthplace in
New Zealand, is only beginning to reach the mainlands of the New and the
Old World.
One is a genus of the tropics and the other is a genus of south
temperate latitudes; and both have occupied the Pacific islands; but
Coprosma naturally finds its most appropriate station on the cool
uplands of Hawaii and Tahiti. We may ask, indeed, whether the great
contrast in the fecundity of the two genera, dispersed as they are in
the same fashion by the agency of frugivorous birds, is to be connected
with questions of relative antiquity or with geographical position. It
would certainly have been a more difficult task in the past, other
things being similar, for a New Zealand genus to stock the temperate
regions with its species than for a tropical American genus to overrun
the warmer regions of the globe. However that may be, the age of
dispersal of both genera is largely over now.
A vast genus like Psychotria, that is not sharply defined from other
genera, presents difficulties to the systematic botanist which are
reflected in a complex synonymy; but there are certain broad facts which
the student of dispersal can gather for himself without much difficulty.
When we look at its distribution in the islands of the open Pacific, we
find that the genus attains its greatest development in the Western
Pacific, there being from thirty to forty species known from Fiji and
quite a dozen from Samoa, and that it shades away as we proceed eastward
and northward, some six species being recorded from Tahiti and the
Marquesas, two from Hawaii, and one from Juan Fernandez near the South
American mainland. The arrangement of the species shows fairly
conclusively that the genus Psychotria, as it is found in the Pacific,
has, like most of the other plants of this era of non-endemic genera,
been derived from the Asiatic side of the ocean. (The absence of species
of this genus from Mr. Cheeseman’s Rarotongan collections seems strange.
It is represented by some species in Tonga, and it is extremely probable
that it will be subsequently found also in the Rarotongan group.)
That the age of dispersal of the genus Psychotria over the Pacific
islands has almost passed away is evident from the circumstance that of
the half-hundred species known from these groups, all but some four or
five are confined to particular groups. There is one species, P.
insularum, that ranges over the South Pacific from Fiji to the Tahitian
region; and there are two or three others that keep up a connection
between the adjacent groups of Fiji, Samoa, and Tonga, the last having
no peculiar species; but, apart from these indications, isolating
influences generally prevail. The two Hawaiian species are both endemic
and are only recorded from the island of Kauai, so that in that
archipelago there has not even been inter-island dispersal of the genus.
For Fiji it would seem from the _Index Kewensis_ and other authorities
that at least two-thirds of the species are confined to the group. Of
the dozen Samoan species only two or three are known outside the
islands. Four out of the five Tahitian species are peculiar, and the
only Marquesan species named by Drake del Castello is endemic. Even the
solitary species of Juan Fernandez is endemic, there attaining the
dimensions of a fair-sized tree. It forms the subject of an illustration
in Schimper’s _Plant-Geography_, page 491.
Speaking generally, birds may be said to have almost ceased dispersing
this genus over the Pacific. This is not because birds have ceased to be
partial to the fruits, but because the frugivorous birds that used to
range over the Pacific archipelagoes now restrict their wanderings to
the limits of a single group. If we find occasionally in other parts of
the world, as in the occurrence of a Florida species of Psychotria in
the Bermudas, some evidence of a dispersal still in operation, this is
nothing more than we observe in the case of a few of the Polynesian
species now. The connection between birds and plants in the Pacific is
discussed in Chapter XXXIII. In this ocean the dispersal of the genus is
now practically dead, and Psychotria presents no exception to that
general tendency towards isolation and differentiation exhibited by most
genera of the tropical Pacific as the result of failure of the means of
dispersal.
CYRTANDRA (Gesneraceæ).
This remarkable genus of shrubs, which forms the subject of an important
memoir by Mr. C. B. Clarke (_De Cand. Mon. Phan._ v. 1883-87), offers,
as Mr. Hemsley remarks, an example of a Malayan genus extending to
Polynesia and there developing numerous species. Of some 180 known
species, about 80 or nearly half are confined to Polynesia, the rest
being mainly Malayan. Of the Polynesian species about thirty are
Hawaiian, twenty Fijian, fifteen Samoan, and twelve Tahitian; whilst
solitary species are restricted to Tonga and Rarotonga respectively.
The most significant feature in the distribution of this genus in
Polynesia is not only, as is pointed out by Mr. Clarke, that every group
has its peculiar species, but that very few species are found in more
than one group, and that even in the same archipelago each island has
its own species. Thus, of the thirty Hawaiian species, all of which are
peculiar to the group, only two or three, according to Hillebrand, are
at all generally distributed over the islands, whilst four-fifths have
not yet been found to be common to more than one island. So again, all
the species found in the Tahitian Group proper are peculiar, with the
exception of one extending to the neighbouring Paumotu Islands; and even
Rarotonga has its own species. In the region comprising Fiji, Tonga, and
Samoa the same rule prevails, only two or three species connecting the
three groups together. There thus seems to be not only a complete
suspension of the dispersal agencies between the various archipelagoes,
but also often between the several islands of a group. This is
particularly to be remarked with the relatively contiguous groups of
Fiji, Samoa, and Tonga, since with most other genera a number of species
are common to all three archipelagoes. “The polymorphism of the Hawaiian
Cyrtandras,” says Hillebrand, “is extraordinary: no single form extends
over the whole group, and not many are common to more than one island.
The variations affect nearly every part of the plant, and branch out and
intercross each other to such an extent that it is next to impossible to
define exact limits of species.” Genera, however, run riot in other
groups of the Pacific besides Hawaii, and Reinecke uses much the same
language with reference to Elatostema, an Urticaceous genus in Samoa,
attributing the wealth of forms to the sensitiveness of the plants to
the varying conditions of station (see Chapter XXVII).
The behaviour of Cyrtandra in the Pacific is rather startling to the
student of plant-dispersal when he reflects on the suitability of the
berries for dispersing the plant through the agency of birds. That the
vegetation of oceanic islands should be of an endemic character is a
fact, remarks Mr. Clarke, that is illustrated by many other orders
besides the Gesneraceæ. But the point we have to remember is that not
only does the genus Cyrtandra display the same prolific character in the
large continental islands of Malaya, such as Java, Sumatra, and Borneo,
each of which possesses at least a couple of dozen species, but that
this seems to be a feature of the tribe Cyrtandreæ and of the whole
order. The genera, as observed by Mr. Clarke, are very continuous in
their areas of distribution, and in the tribe Cyrtandreæ there are very
few species that extend to more than one region, whether on the mainland
or in an oceanic archipelago. In the Himalayas, he says, closely allied
species of Didymocarpus are confined to single districts, although there
appears no reason either in soil or climate why they should not spread
to the adjacent valleys.
There is therefore, we may infer, nothing peculiarly characteristic of
insular floras in this prolific display of the genus Cyrtandra in the
Pacific, except that it is rather more pronounced in an oceanic group
than in a continent. The same general cause is working alike in an
island in mid-ocean, in a large continental island bordering the
mainland, and on the mainland itself. With the Pacific Cyrtandras as
with the British species of Rubus the variability may be so great that
the ordinary agencies of dispersal fail to keep it in check; and when,
as in the Pacific islands, the suspension of the activity of these
agencies is complete, the formative energy of the species knows no
bounds other than the determining limits of station. Our lesson from the
Pacific Cyrtandras is therefore this. The isolation of the oceanic
archipelagoes may not explain the endemic character of the flora, but
only the extreme degree to which the endemism is carried. When a genus
is in its prime, it can defy all the limiting conditions imposed by
similarity of station and by free and unchecked means of dispersal, the
essential marks of a species or a genus having probably in their
development little or no connection with environment.
The Cyrtandras of the Pacific Islands are most frequent where vegetation
is rank, as in moist woods, in humid valleys, and in shady ravines and
gorges; but they may also occur in more exposed and drier stations. They
often grow gregariously, and Schimper says the same of them in the Java
forests (_Plant-Geography_, pp. 291, 297).
The fruit of the genus is described by Clarke as a fleshy or a
coriaceous berry. Almost everywhere in the Pacific groups the berry is
white and fleshy; but it is noteworthy that out of the nine Tahitian
species where the fruit is particularised by Drake del Castello, in two
cases it is designated a capsule and in seven a berry. It is in this
connection worth remarking that in Malaya other genera of the tribe
often have capsular or dry and coriaceous berries. The conspicuous white
berries of the Pacific species would readily attract birds, and their
minute roughened seeds scattered through the pulp might readily adhere
to their plumage or even be ejected unharmed in their droppings. As
respecting the capacity for dispersal, the Pacific Cyrtandras come near
the Hawaiian endemic genera of Lobeliaceæ with baccate fruits and minute
seeds. Speaking of Malayan genera of the tribe Cyrtandreæ, Mr. Ridley
says that their dry, dull-coloured, and inconspicuous corky fruits are
often devoured by animals. The seeds, on account of their roughened
surface, adhere to rocks and other surfaces and readily germinate.
FREYCINETIA (Pandanaceæ).
If there is any genus of tropical plants to which the student of
distribution can look for guidance in the region of the Pacific, it is
to Freycinetia as dealt with by Dr. Warburg in his monograph on the
order (Engler’s _Pflanzenreich_, iv. 9, 1900). Its characters and its
distribution are well defined; and here, if anywhere, we might be able
to work out the history of a genus. In the words of the German botanist,
it stands quite apart from Pandanus and Sararanga, the two other genera
of the order. When Hillebrand was preparing his work on the Hawaiian
flora, more than a quarter of a century ago, only about thirty species
were known. Warburg’s list, excluding doubtful forms, comprises sixty
species, and even this number the author surmises will be doubled in
future years. The later investigators, however, have not materially
extended the range of the genus; and the statement of the botanists of a
generation ago, that it extends from Ceylon through Malaya and Australia
to New Zealand, and is found on almost every elevated island of the
Pacific, can only be supplemented by extending its area to the Asiatic
mainland in Burma where a wide-ranging Malayan species exists.
It is, however, remarkable that no endemic species can be with certainty
accredited to the mainland of Asia either in Burma or in the Malay
peninsula where the genus also occurs. The Malayan region from Java to
the Philippines possesses quite three-fifths of the species, and it is
singular how few wide-ranging species there are. The Philippine Islands,
Borneo, Celebes, Sumatra, Java, New Guinea, &c., have all their own
species, the only wide-ranging plant being Freycinetia angustifolia,
which occupies the region from Burma to Java and Borneo. So also in the
Pacific, there is no widely distributed species, every group possessing
its own plant or plants, and there does not appear to be any Freycinetia
that is common to two groups. Thus, Hawaii and Tahiti each have their
own species. Rarotonga, according to Cheeseman, owns a peculiar but not
yet fully described form. Samoa has two and Tonga has one species.
Westward from Tonga and Samoa the numbers of species increase, Fiji
possessing five and New Caledonia four. Australia and New Zealand each
claim two species as their own.
Dr. Warburg, who has studied the genus in its home, remarks on page 43
that none of the species possess any means of dispersal enabling them to
cross an ocean; and he connects with this the fact that the genus is
only found (to use his own words) on islands like those of Samoa,
Tahiti, and Hawaii, that possess a “palæobiotic” nucleus
(_paläobiotischen Kern_) and not on islands like the Bonin Islands of
new formation (_auf Neubildungen_). This attitude towards the problem of
plant-distribution in the Pacific is backed by a great experience; but
it is one, of course, that is directly opposed to the line of argument
followed in these pages; and it is needless to say that it is not
encouraging to the student of plant-dispersal. Yet one could hardly look
upon the islands of the Tongan Group with their representative of the
endemic Freycinetias as of more ancient origin than the Bonin Islands
that have none; and plants that find their homes on the peaks and in the
forests of mountainous islands would rarely find a suitable station on
the low coral islands of the Pacific. It is, however, noteworthy that
Professor Schimper is inclined to include a species of Freycinetia as
amongst the strand-flora of the coral islands of the Java Sea (_Ind.
Mal. Strand-flora_, p. 134). With regard to the question of the means of
dispersal of Freycinetias, it will at once be shown that these plants
possess many opportunities for dispersal by birds.
Though in our own time dispersal by birds between the various Pacific
archipelagoes is often largely suspended, the inter-island dispersal in
each group is usually active through the agency of birds, now like the
plants they distribute confined to each group. Thus with Freycinetia we
find that, notwithstanding that each Pacific group is, as regards this
genus, isolated from the others, the separate islands, as in the case of
those of Hawaii, may possess a common species dispersed over the area.
The ripe fruit, which consists of a number of berries in a head or
spike, is juicy and pulpy, and contains in each berry a large number of
minute oblong or fusiform seeds, usually one or two millimetres long and
possessing thick toughish tests. Birds, indeed, are fond of pecking at
the ripe fruit-heads in Hawaii. Thus we learn from the _Aves
Hawaiienses_ of Wilson and Evans that a Grosbeak (Psittacirostra) and
the Hawaiian Crow (Corvus tropicus) feed principally on ripe Freycinetia
fruits, the seeds having been often found by Mr. Wilson in the stomach
of the former bird. No doubt these birds distribute the seeds over the
islands of the group. Mr. Perkins tells me that the Grosbeak is found
unmodified all over the group, and that it no doubt frequently gets
carried _nolens volens_ from one island to another. In his memoir on the
birds in the _Fauna Hawaiiensis_, he remarks that the essential food of
the “Ou,” the native name of this bird, is the fruiting inflorescence of
Freycinetias. The “Oo” (Acrulocercus) and the Hawaiian Crow above
mentioned, as he also observes, feed on these ripe red fruits. Like Mr.
Wilson, he sometimes found the Crow absolutely filled with this food to
the exclusion of all others (see Chapter XXXIII). Facts of a similar
kind came under my notice whilst in these islands. Thus on one occasion
I observed, on a leaf below a fruit-head that had been partly eaten by a
bird, a pellet half an inch long composed entirely of Freycinetia seeds
well soaked with the gastric juices and apparently only recently
disgorged. Sir W. Buller refers to different New Zealand birds, as the
Banded Rail (Rallus philippensis), the Kaka Parrot (Nestor
meridionalis), and the “Tui” (Prosthemadera), that live on the “sugary
flowering spadices” of Freycinetia Banksii. One can legitimately suppose
that they also attack the juicy berries. It is singular that as we learn
from Dr. Warburg (p. 17), Flying-Foxes (Pteropidæ) feed on the flowers
and top-leaves of many species of Freycinetia, and he considers that
they would aid in fertilisation by carrying about the pollen in the hair
of the head. Here again it would seem to us highly probable that whilst
brushing past a ripe fruit-head these bats might readily carry away in
their fur some of the minute seeds, which in the fresh berry are
“sticky” or adhesive.
Just as it was possible in the case of Coprosma in the South Pacific
(see page 296) to connect its distribution with the range of the Purple
Water-Hens (Porphyrio), so it may perhaps be legitimate to associate the
range of Freycinetia over Polynesia with the distribution of the
Honey-Eaters (Meliphagidæ) in the Pacific, a family sometimes possessing
peculiar genera as in New Zealand and Hawaii, and one in which the
species have usually a very confined range, being sometimes limited to a
single island (Newton in _Encycl. Brit._ xii. 139). To this family
belongs the New Zealand “Tui” above mentioned; and it may be remarked
that these birds as a rule feed on soft fruits, such as figs, and
bananas. It is to Acrulocercus, one of the Hawaiian genera of the
Meliphagidæ, that Mr. Perkins refers me, on my asking him to name some
of the fruit-eaters in that group.
These climbing shrubs, as Dr. Warburg observes, mostly frequent the
tropical forests up to 4,000 feet and over. Though their most familiar
habit is as tree-climbers in the forests, in localities where there are
no trees they adopt a trailing habit and cover mountain peaks and ridges
with a dense growth to the exclusion of almost all other plants. Many a
peak in the Pacific islands would be inaccessible if it were not for the
dense growth of these plants on their precipitous sides. It was owing to
the friendly aid of a tangled mass of Freycinetia stems that Lieutenant
Heming and myself were able to clamber to the summit of Fauro Island
(1,900 feet) in the Solomon Group, where I discovered a tree that under
the name of Sararanga forms the type of the third genus of the
Pandanaceæ.
Whilst describing their station, it will be of interest to also record
the altitudes at which these plants have been observed in the tropical
Pacific. Since they can be independent of trees and are as much at home
on treeless rocky peaks and mountain crests, the upper limit would
usually be determined by climatic conditions, abundance of rain and
great humidity being the chief requisites; but, as will be seen below,
this limit does not seem to be reached in the tropical islands of the
South Pacific except perhaps in Tahiti. In the Fijis the Freycinetias
ascend to the highest mountain peaks. Thus, three of the species
discovered here by Seemann were found at elevations of about 4,000 feet
on Voma Peak in Viti Levu and in the highlands of Taviuni. In Vanua
Levu, as I found, they cover the highest peaks 3,500 feet above the sea.
They are especially abundant on the lofty mountain ridges, and clothe
the higher slopes of the Mbatini Ridge which terminates in the highest
peak of the island. In no locality did I find them growing in such
densely tangled masses as on the long ridge-like crest that forms the
upper part of Mount Freeland, 2,740 feet above the sea. For more than an
hour in order to reach the summit I had to clamber along the crest of a
ridge covered with a dense growth several feet deep of these trailing
plants, without touching the ground beneath.
In Samoa, as we learn from Reinecke, Freycinetias are common on the
mountain ridges, climbing the trees and forming also a dense undergrowth
covering the ground and concealing the rocks. They occur at all levels
from 1,000 feet above the sea up to the highest region of Savaii, rather
over 5,000 feet in elevation. In Rarotonga, according to Mr. Cheeseman,
the Freycinetias are very abundant on the mountains, which reach a
height of 2,200 feet, the plants scrambling up the trunks of trees or
over rocks and frequently rendering the forest almost impenetrable. In
Tahiti, Nadeaud tells us, the Freycinetias often cover in an
inextricable network the sides of the valleys at elevations of 2,000 to
3,300 feet, extending in their vertical range from the lower levels of
the island to the highest inaccessible peaks which attain a maximum
height of about 7,300 feet.
These plants in the Hawaiian group are common in the lower woods as
Hillebrand informs us, that is to say, at elevations of 2,000 or 3,000
feet. During my descent from Mauna Kea through the Hamakua forests on
the north-east side I observed that the Freycinetias commenced at an
altitude of 3,900 feet, and that they attained their greatest
development between 3,200 and 2,000 feet. These plants ascended quite a
thousand feet higher on these mountain slopes than the Bird’s Nest Fern
(Asplenium Nidus), which reached an altitude of 2,800 feet. In the
forests on the west side of Mauna Loa they were abundant at altitudes of
3,500 to 4,000 feet and were not noticed above 4,500 feet. On the slopes
of Mount Eeka in West Maui they abounded between 3,500 and 4,400 feet.
In those localities where the forest descends to the sea, Freycinetias
occur at the coast, and on Oahu they are often found at elevations under
a thousand feet.
I have but few data showing the altitude obtained by Freycinetias in
other regions, as, for instance, in their most southerly habitat in New
Zealand, where they give a tropical luxuriance to the forests, or in
their chief home in Malaya. From Schimper’s observations
(_Plant-Geography_, p. 293) it would seem that they thrive in the Gedeh
forest of Java at elevations of about 5,000 feet. Except for the lower
levels, Warburg makes but few references to this subject in dealing with
the species. It appears to me that some very interesting results might
be obtained by comparing the vertical range of this genus in different
regions, as, for instance, in New Zealand and in Borneo or in Java. We
might get indications that since the age of Freycinetia began the
climate in tropical latitudes has been getting warmer, and that the
erstwhile plants of the lower levels are now as a result climbing the
mountain slopes. The student of distribution may find here a genus that
has been “cornered” not only in space and time, but as regards its
conditions of existence. Since it is obvious that during a gradual
increase of temperature it would ascend the mountains and during a
lowering of temperature it would descend to the plains, it follows that
in the mountains of an oceanic island it might be driven into the sea or
await extinction on a mountain-top. In the tropics also there would be
no escape during a gradual increase of temperature. Here again it would
make its last stand on the strand, and, forced to choose between Death
and Adaptation, the genus might select the latter alternative and
present us with a startling new form. In this sense Freycinetia seems to
offer itself as “fair game” for the speculative botanist, and at all
events he will be able to interrogate it as to the connection between
its existing range of altitude and the climatic conditions of the
earlier phases of its history.
The Freycinetias bear the same name over Polynesia, “ie-ie” in Hawaii,
“ie” and “ie-ie” in Tahiti and Samoa, which appear in their full form in
the Rarotongan and Maori “kie-kie.” The secret of the wide distribution
of the name lies in the circumstance that this is a mat-word over much
of Polynesia, as in Fiji, Tonga, Samoa, the Gilbert group, Tahiti, &c.,
Freycinetia leaves being often employed for making mats, as in Samoa and
New Zealand. The same word is applied in some groups to small species of
Pandanus that were also used in mat-making. Thus in Fiji “kie-kie” was
not only the name for a mat-dress, but also of Pandanus caricosus that
supplied the material. In the home of the Polynesians in Malaya and its
vicinity the same word for mat and Pandanus occur. Thus, “gerekere” in
the Motu dialect of New Guinea and “keker” or “kekel” in Amboyna are the
names of small species of Pandanus employed in mat-manufacture; whilst
“kihu” and “kiel” in Celebes are the words for the mats themselves.
Therefore in one form or another the word, originally applied to the
mats, but now often restricted to the plants from which the materials
were derived, ranges over the great region extending from Malaya to New
Zealand, Tahiti, and Hawaii, and, as I have shown in the table given in
my paper on Polynesian Plant-Names (_Journ. Victor. Inst._, London,
1896), it may be traced even to Further India, as in Annam, and to
North-East Australia. It thus covers the area to which the migrations of
the Polynesians of the Pacific have been confined, and it covers also
the area of the genus Freycinetia. There is something far more than mere
analogy between man and plants in their occupation of the Pacific
islands. The plants are Malayan and the Polynesians are from Malaya
also, whilst in both man and plants we experience the same difficulty in
explaining their dispersal over the ocean. Divesting his mind of all
previous conceptions, the ethnologist might profitably study _de novo_
the dispersion of man in the Pacific from the standpoint of
plant-dispersal (see Chapter XXVIII).
SAPINDUS AND PHYLLANTHUS.
Brief reference can alone be made to these two genera. Foremost comes
Sapindus, which is represented by two endemic species, one in Hawaii and
one in Fiji, and by another species, found in Tahiti, the Marquesas, and
Easter Island, which is identified by some botanists with the well-known
American “soap-tree,” S. saponaria. There are several difficulties
connected with the presence of this genus of the Old and New World in
the Pacific. Not the least of them is connected with the transport of
the large seeds of this genus, an inch in size, to the isolated Hawaiian
Group, where it is represented by a solitary endemic species in the
island of Oahu. The fleshy mesocarp of the fruits might attract birds;
but it is not easy to perceive how birds could carry such large seeds
over some 1,500 or 2,000 miles of ocean. Yet the same difficulty exists
with a few other genera, such as Osmanthus and Sideroxylon, that are
only represented in Hawaii by endemic species, genera which require the
agency of birds to explain their occurrence unless we wish to postulate
a continental connection for this group. (See under those genera in
Chapter XXVII.)
The large Euphorbiaceous genus Phyllanthus, spread universally over the
tropics and containing some 500 known species, clearly indicates by its
distribution in the Pacific islands that genera with dry fruits, such as
are typical of the order, are as widely distributed and just as much at
home in these islands as the genera with fleshy fruits, such as
Psychotria and Cyrtandra. The small trees and shrubs of Phyllanthus are
common in dry, open, partially wooded districts near the sea-border. The
genus attains its greatest development in this ocean in New Caledonia
and Fiji; and since the number of species diminishes the further we
penetrate the Pacific, it can be scarcely doubted that the genus has
entered this ocean from the west. In Fiji there are at least 20 species,
of which probably half are not recorded from elsewhere. In Samoa there
are seemingly but few peculiar species. In Hawaii there is only one
indigenous species, and that is endemic. The genus, however, has
developed a lesser centre of distribution in East Polynesia, there being
about a dozen species known from Tahiti and the Marquesas, of which half
are peculiar to one or other of those groups. From experiments made by
me in Fiji on the fruits and seeds of two species it was evident that
they possessed little or no capacity for dispersal by the currents. We
look, therefore, to the birds, and in this connection it is of interest
to note that this genus is included amongst those known to be dispersed
by birds in the Pacific, some of the fruits having been found in the
crops of fruit-pigeons shot by Prof. Moseley in the Admiralty Islands
(_Bot. Chall. Exped._, Introd. 46; iv. 308).
PRITCHARDIA (Palmaceæ).
This genus of Fan Palms supplies an instructive lesson for the student
of plant-distribution, more especially with reference to the loss of the
endemic reputation of a genus. Regarded by the earlier botanists who
visited the Pacific as identical with the familiar Asiatic Talipot Palm
(Corypha umbraculifera), the Fan Palms of this region, as represented in
Fiji and Hawaii, were subsequently placed by Seemann and Wendland in a
new genus restricted to Polynesia and named after a former British
Consul in Fiji. Since that time it has lost its reputation as a
peculiarly Pacific genus, since a species (Pritchardia filifera) has
been found lingering in a few valleys in Arizona, where it enjoys the
distinction of being the most northerly in station of all the world’s
palms (Linden in _Illustr. Hort._ vol. 24, 1876-77). It would thus
appear that the Pacific islands have derived this genus of palms from
the western part of North America, but the whole question is beset with
many difficulties, and not the least is that connected with the
confusion that seems to reign in several cases as regards the allocation
and identity of the species.
Six species are named in the _Index Kewensis_, viz.: Pritchardia
macrocarpa, restricted to Hawaii; P. martii and P. gaudichaudii, of the
Pacific islands; P. pacifica, assigned to Fiji; P. vuylstekeana, from
the Paumotus; and P. filifera, from the west side of North America.
Though it is sometimes difficult to reconcile this account of the
distribution of the genus in the Pacific with views held by other
botanists, it offers the safest basis for the future investigation of
the subject. It would be, however, necessary to remember that
Pritchardia gaudichaudii and P. martii are regarded by Hillebrand as
peculiar to the Hawaiian Islands, and that the exact locality of the
Paumotu species is not very definitely settled, if it depends on the
remarks made on this species in the _Gardeners’ Chronicle_ for 1883. No
mention is indeed made by Drake del Castillo of any Tahitian or
Paumotuan species.
Whilst in Hawaii and Fiji I was much interested in these palms, and the
following remarks are merely intended to be a contribution to the
subject. According to Seemann, Hemsley, Drake del Castillo, and Burkill,
Pritchardia pacifica, which often attains a height of thirty to
thirty-five feet, occurs in Fiji, Tonga, Samoa, and the Marquesas, but
it does not exist in Tahiti, and Cheeseman does not include it in the
Rarotongan flora. Except in the Tonga Group, where, according to Lister
as quoted by Hemsley, the palms form conspicuous objects along the
weather shore of the island of Eua, this species is rarely found in the
wild state in the South Pacific. This especially applies to Fiji, as Mr.
Horne also observes; and at most one is accustomed to see (to employ the
words of Dr. Seemann) one or two trees outside a village which are
reserved, as in many parts of Polynesia, for the use of the chiefs who
employ the leaves for fans and for other purposes. But even this reason
for preserving the palms scarcely now exists in Fiji, and at the time of
my sojourn in Vanua Levu (1897-99) the trees were rare enough to be
regarded as curiosities. In the Marquesas, according to Bennett (quoted
by Seemann), they grow in groves in the valleys of the interior. Dr.
Reinecke does not even include the species in the Samoan flora, but
mentions it with the Date-Palm (Phœnix dactylifera) as if it were
recently introduced. It was, however, found in that group by the United
States Exploring Expedition about 1840, and this is evidently the palm
referred to by Captain Cook as existing at his time in the Tongan Group.
The Hawaiian species of the palm appear to be three in number,
Pritchardia gaudichaudii and P. martii, both regarded by Hillebrand as
confined to the group, and P. macrocarpa of Linden, also endemic
(_Illustr. Hort._ vol. 26). The two first-named species are evidently on
the road to extinction in the wild state, and often find their last
refuge on rocky, almost inaccessible, inland cliffs. Pritchardia
gaudichaudii, about twenty feet in height, is found in the wild state,
as we learn from Hillebrand, on the islands of Molokai and Hawaii. It
was at one time frequently met with near native dwellings; but during my
sojourn in 1896-97 on the last-named island it was not at all frequent,
and as a rule only came under my notice occasionally in clumps of three
or four trees on the Kona and Puna coasts, as near Kiholo, Milolii, and
Kalapana. However, it was more frequent in the Waimanu district of
Kohala in the same island. Here I noticed it growing in clumps in
precipitous rocky situations at elevations ranging from 1,200 to 2,000
feet. The other palm mentioned by Hillebrand, P. martii, is only five or
six feet high, and is confined mostly to Oahu and Molokai.
The agency of man in introducing these interesting Fan-Palms into the
Hawaiian Islands seems out of the question, since they are home
productions in a specific sense and are doubtless ancient components of
the flora; and, of course, grave objections exist on ethnological
grounds, if this genus had originally its home in America. With
reference, however, to Pritchardia pacifica of the South Pacific, it is
not unlikely that man has aided in the distribution of a palm mainly
preserved by planting in and about the villages and set apart from time
immemorial for the use of the chiefs.
In this connection the aboriginal names are of some importance and may
be very briefly here referred to. The Fijian “Viu,” the “Piu” of Samoa,
Tonga, and Futuna, and the Tongan “Biu” are forms of the same name
applied to this palm all over West Polynesia; and I have shown in my
paper on Polynesian Plant-Names that in the form of “Firo” in the
Solomon Islands (Bougainville Straits) and of “Wiru” in Sundanese, one
of the Malayan languages, the same name is given to another genus of Fan
Palms, namely, Licuala. But since these West Polynesian names do not
always conform with the laws of consonantal interchange in this region,
they cannot all be considered as indigenous in the languages concerned.
If, for instance, “Viu” is an indigenous Fijian name, as no doubt it is,
since it follows the phonetic laws affecting the Malayan and Fijian
languages, “Piu” must be a foreign word in Samoa and Tonga, and “Biu”
must be another introduced Tongan name.... The Fijians have in “Sakiki”
(contracted into “Saii” in the Somosomo dialect) another name for this
palm. This is probably derived from “Kiekie,” a mat-word in different
forms in various Polynesian groups, and applied in many islands to the
plants that supply the materials for mat-making, such as Pandanus and
Freycinetia.
The Hawaiian generic name of “Loulu” for these palms appears to be quite
local; but it may possibly have a common origin with “Roro,” one of the
Fijian names of Cycas circinalis. It is pointed out by Hillebrand that
the Hawaiian name of the edible kernels of these palms, “Hawane” or
“Wahane,” occurs in the Marquesas as “Vahana” applied to the palm, a
comparison that is on linguistic grounds quite legitimate. “Vaake” is
another Marquesan name, which recalls “Vakoa,” the Malagasy word for
Pandanus.
When we compare the variety of the names of the Pritchardia fan-palms in
the Pacific Islands with the prevailing uniformity of the names of
cultivated plants transported by the aborigines in their migrations from
Malaya, such as the taro, the yam, the sugar-cane, the coco-nut, and the
Malay-apple, we perceive that the testimony of the names points to the
same conclusion as the botanical evidence, namely, that the ancestors of
the Hawaiians found these palms in the group at the time of its
occupation. In the South Pacific much uncertainty prevails. The
ancestors of the West Polynesian peoples evidently brought the word for
a fan-palm from their Malayan home; but it is doubtful if they found
Pritchardia already established in all the islands; and the apparent
home of the genus in America prevents us from attributing to a palm,
that is by some botanists regarded as confined to the Western Pacific, a
home in the neighbouring regions to the west. There is thus a lack of
agreement between the botanical and ethnological indications as regards
the original American origin of Pritchardia in the South Pacific.
There remain then the agencies of the currents and of birds. A singular
feature in the distribution of the Hawaiian species, Pritchardia
gaudichaudii, at once affords a clue as concerning the dispersal in the
North Pacific. Dr. Hillebrand remarks that this palm covers part of Bird
Island, a small volcanic rock forming an outlier of the Hawaiian group
about 400 miles north-east of Kauai. Here the agency of birds is
suggested, since it is scarcely likely, though, as shown below, not
impossible, that stranded fruits of the palm could have established
themselves in this fashion. Mr. Perkins has an interesting note on the
food of Ciridops anna, an Hawaiian bird, now nearly extinct, that feeds
principally on the blossoms and unripe fruits of the Loulu palms,
probably of this species. The drupes when fresh have a somewhat fleshy
mesocarp and are about 9/10 of an inch (22 mm.) across, and their
crustaceous inner shell would undoubtedly fit the seeds for dispersal by
frugivorous birds like pigeons. The fruits of the other two Hawaiian
species are considerably larger, that of P. macrocarpa being, according
to Linden, of the size of a nut of Juglans regia, that is, about 1-1/8
inch or 29 mm., whilst that of P. martii, as we learn from Hillebrand,
is from 1-1/2 to 2 inches or 37 to 50 mm. Allowing for the variation in
size of the fruits within the limits of the genus, there need be no more
difficulty in assuming that the original species had fruits that could
have been brought by birds, than in holding that the fruits of
Elæocarpus have been carried to Hawaii in the same fashion. The drupes
of Pritchardia pacifica are barely half an inch in diameter. They are
fitted by reason of their hard crustaceous endocarp for dispersal by
fruit-pigeons; and I may here add that these birds are known to
distribute the fruits of other palms, such as Kentia and Areca, in the
islands of the South Pacific (_Bot. Chall. Exped._ iv. 308, 312).
Both in Hawaii and in Fiji I experimented on the capacity of Pritchardia
drupes for dispersal by the currents. Those of the Hawaiian species, P.
gaudichaudii, have when well dried a light buoyant rather fibrous
mesocarp which enables them to float in the case of a good proportion of
the fruits for at least five weeks. I had no opportunity of testing the
buoyancy of the fruits of P. martii, another Hawaiian species; but,
judging from the existence in the coats of a fibrous layer as described
by Hillebrand, they ought to display some floating power. The fruits of
P. pacifica, the South Pacific species, lack the light buoyant covering
of the Hawaiian species above referred to, and display little or no
floating power even after drying for weeks. Looking at the results of
these experiments, it would seem that it is not impossible that Hawaii
received the genus through the agency of the currents; but it seems
scarcely probable, since it could only have been derived from America,
and the American species grows in the interior of the continent and not
near the sea-border. The possibility of course exists; but I am inclined
to attribute the presence of Pritchardia in Hawaii to bird-agency.
My position from the standpoint of dispersal with regard to Pritchardia
in the Pacific is this. The Hawaiian species I would consider as
American in origin. The Marquesan species, unless recently described,
still awaits detailed investigation. The West Polynesian species of Fiji
and Tonga, according to the principles of distribution prevailing in the
South Pacific, ought to hail from the west.
_Summary._
(1) Whilst the earliest age characterised by the Coniferæ was restricted
to the Western Pacific, and whilst the following age of the Compositæ
and Lobeliaceæ, mainly American in their affinities, was concerned with
the regions of Hawaii and Tahiti, we have now to discuss the Malayan era
during which the bulk of the plants were derived from the nearest
tropical regions of the Old World. Here we have to deal with the
low-level flora of Hawaii, that is to say, with the plants of the levels
below 4,000 or 5,000 feet, and with almost the entire floras of the
areas of Fiji-Samoa and of East Polynesia. The whole of the tropical
Pacific is here concerned, and not a portion of it, as in the two
preceding eras; and in our comparison we shall see that there are two,
and not as heretofore three, regions to be regarded—the Hawaiian in the
North Pacific, and the whole Polynesian area of the South Pacific
extending from Fiji to Tahiti.
(2) Here the frugivorous bird has been the principal agent in dispersing
the plants, quite two-thirds of the genera possessing drupes or berries
that would attract such birds.
(3) The genera representative of the first part of this era are those
which have only peculiar species in Hawaii, and are composed in the
South Pacific either entirely of peculiar species or sometimes of a
mixture of endemic and non-endemic species. It is an era of complete
isolation in Hawaii and often of a partial connection between the groups
of the southern region. Except to some extent in the South Pacific, the
dispersing agencies are now no longer active between the groups.
(4) Amongst the genera typical of this period are Pittosporum, Gardenia,
Psychotria, Cyrtandra, and Freycinetia.
(5) The two genera of the Rubiaceæ, Psychotria and Coprosma (the last
belonging to the mountain-flora), appear to be well suited for the
investigation of the effect on distribution of the geographical position
of the home of the genus, the first with 600 to 700 species distributed
over the tropics of the Old and New Worlds, the second with some sixty
species having its home in New Zealand.
(6) From the Pacific Cyrtandras we derive the lessons that the display
of great formative power in a genus may not be a peculiarity of an
insular flora; that the isolation of an oceanic archipelago does not
necessarily induce “endemism,” but merely intensifies it; and that the
production of new species within the limits of a genus like Cyrtandra
may be nearly as active on the mainland as in an island in mid-ocean.
(7) From the Freycinetias we learn that it may be possible to connect
the distribution of a genus of plants with that of a genus or a family
of birds. Just as in Chapter XXIV we endeavoured to connect Coprosma and
Porphyrio (the Purple Water-Hens), so we here suggest a connection, in
their range over the Pacific, between the Freycinetias and the
Meliphagidæ (the Honey-eaters), a connection that in the last case at
least belongs to the past.
(8) From the genus Phyllanthus we learn that genera with dry fruits may
be as widely distributed and may display the same formative power in the
Pacific as those with fleshy fruits that would seem much more likely to
be dispersed by birds. Here again we obtain an indirect indication that
species-making in these islands is not altogether dependent on
isolation.
(9) In the case of the genus Sapindus we are apparently compelled to
infer that its large seeds (in the present species an inch in size) have
been transported by birds to Hawaii. Yet in point of size the
difficulties here raised are no greater than those arising from the
existence of such genera as Sideroxylon and Elæocarpus in Hawaii, the
fruits of which are known to attract frugivorous birds.
CHAPTER XXVI
THE MALAYAN ERA OF THE NON-ENDEMIC GENERA OF FLOWERING PLANTS
(_continued_)
THE AGE OF WIDE DISPERSAL OVER THE TROPICAL PACIFIC (_continued_)
The widely dispersed genera that are as a rule not entirely
represented by endemic species in any
archipelago.—Elæocarpus.—Dodonæa.—Metrosideros.—Alyxia.—Alphitonia.—Pisonia.—Wikstrœmia.—Peperomia.—Eugenia.—Gossypium.—The
last stage in the general dispersal of plants of the Malayan
era as illustrated by the widely-dispersed genera having
as a rule no peculiar
species.—Rhus.—Osteomeles.—Plectronia.—Boerhaavia.—Polygonum.—Pipturus.—Dianella.—Summary.
A LATER period in the era of the general dispersal of Malayan plants
over the Pacific is indicated by those genera that as a rule are never
entirely represented by endemic species in any archipelago. Hawaii now
comes into touch with the world outside, and all the groups possess some
connecting link. But the beginning of the effect of the isolating
influence is shown in the association in each principal archipelago of
peculiar species with those that occur in other groups.
We see here illustrated in all but the final stage that process by which
a solitary widely-ranging species, alone representing its genus, becomes
ultimately in each group the parent of a number of peculiar species. The
polymorphous, or extremely variable, species plays in this period the
all-important part. The earliest stage is exhibited by such genera as
Alphitonia, Dodonæa, Metrosideros, Pisonia, and Wikstrœmia, that possess
in the tropical Pacific a solitary widely-ranging species, varying
independently in every group and giving rise to forms that, in their
degree of differentiation, sometimes approach a specific value. Later
stages are shown when the polymorphous species, having done its work of
distributing the genus, settles down and “differentiates” in every
group; and this we see now illustrated in the genera Elæocarpus, Alyxia,
Peperomia, and others.
The bulk of the genera of this period, of which only a few can be
mentioned here, hail from the tropics of the Old World through Malaya.
Thus Alyxia, Elæocarpus, Morinda, and Wikstrœmia are Malayan; whilst
genera like Eugenia, Peperomia, and Pisonia, that occur in the Old and
New Worlds, can similarly be traced to the Asiatic side of the ocean by
the distribution of their species. Others again have their home in New
Zealand like Metrosideros, or in Australia, as with Dodonæa and Scævola.
None are exclusively American. Some of the genera, as Morinda and
Scævola, have littoral as well as inland species; but, as shown in
Chapter XIV, there is rarely anything to suggest a derivation of the
inland from the coast species, both being, from the standpoint of
dispersal, of independent origin.
About half of the plants have fleshy or sappy fruits (drupes and
berries) that would attract frugivorous birds, such as we find in
Xylosma, Elæocarpus, Eugenia, Scævola, Wikstrœmia, &c., whilst the
others have often dry capsular fruits, with minute seeds as in
Metrosideros, or with larger seeds as in Dodonæa. Some of them, like
Pisonia, have fruits that excrete a viscid material that causes them to
adhere firmly to plumage. Birds both granivorous and frugivorous have
been actively at work; and there are few difficulties relating to
dispersal connected with the genera, except with such as Gossypium and
Elæocarpus.
I will adopt the method employed in the preceding chapter of discussing
in detail from the standpoint of dispersal some of the genera that came
most frequently under my notice, or in which I am greatly interested,
and of dealing briefly with some of the rest. Those dealt with in other
connections will not be treated.
ELÆOCARPUS (Tiliaceæ).
This is a genus of trees containing, according to the _Index Kewensis_,
about 130 species, most of which are confined to tropical Asia,
including Malaya; but a fair number occur in the Pacific region, in
Australia, New Zealand, and the islands of the tropical Pacific, and the
genus is also found in Japan. It will thus be seen that Elæocarpus is
not only a continental but also a typical insular genus. It has reached
not only some of the most isolated island-groups of the Pacific, but it
is to be found also in the smaller islands of the Indian Ocean, there
being an endemic species in Mauritius. Amongst the Pacific Islands, a
region with which we are more immediately concerned, it has been
recorded from the Solomon Islands, New Caledonia, Fiji, Tonga, Samoa,
Rarotonga, and Hawaii. It is strange that the genus is not accredited to
Tahiti, but since it is represented in Rarotonga we may regard it as not
altogether absent from East Polynesia. Reinecke does not include it
amongst the Samoan plants, but Horne, in a short list of plants
collected in Upolu about 1878, mentions Elæocarpus græffei, a Fijian
species (_Year in Fiji_, p. 285).
New Caledonia represents the principal centre of the genus in the
tropical Pacific, thirteen species being accredited to it in the _Index
Kewensis_. Seemann found six species in Fiji, a number that does not
seem to have been added to by Horne. Of these one is found in Tonga and
Samoa, and of the rest perhaps most are peculiar; but one of them is
closely allied to a second peculiar Tongan species. Tonga possesses the
two species just alluded to, whilst Rarotonga and Hawaii have each a
peculiar species.
From an interesting comparison made by Mr. Burkill of some of the
Polynesian species, it would seem that Elæocarpus, if not actually
possessing a widely-spread polymorphous species in the tropical Pacific,
presents us with the next stage in the differentiation of the species.
Thus, he says in his paper on the flora of Vavau that an endemic Tongan
species, E. tonganus, is allied to three different species—E. græffei
from Fiji, E. floridanus from the Solomon Group, and E. glandulifer from
Ceylon—three species, he remarks, which are “so closely allied that it
is possible to regard them as insular subspecies.” It would thus appear
that some of the species of the Western Pacific are almost in touch with
Asiatic species. It would be of importance to determine whether some
affinity can be detected between the species of this part of the Pacific
and some of the widely-ranging species of Indo-Malaya, such as E.
ganitrus and E. oblongus. Mr. Burkill goes on to say that the solitary
Hawaiian and Rarotongan species are closely allied, an inference which
is of interest as indicating the route by which Hawaii received its
species. The genus, we may fairly infer, once possessed a widely-ranging
polymorphous or very variable Asiatic species in the tropical Pacific;
and we see it now in the next stage of specific differentiation in
various far-removed regions. In this connection Seemann significantly
remarks that all the Fijian species are evidently very local in the
group.
It will be appropriate here to refer briefly to the station and mode of
occurrence of the species. They occur most typically as forest-trees,
often of considerable height. In New Zealand, according to Hochstetter,
they form a feature in the temperate rain-forest; and, as we learn from
Kurz, they are similarly conspicuous in the tropical rain-forests of
Pegu. To this seeming indifference to the varying thermal conditions of
different latitudes we shall have subsequently to refer again. The tree
of the Hawaiian Group, as Hillebrand tells us, is common in the forests
of Oahu and Kauai, but is scarce in Maui and Hawaii, a singular
distribution that may be due to the inflorescence being “often
monstrously deformed by oviposition of some dipterous insect.” The
Rarotongan species, according to Cheeseman, is common throughout the
island from the sea-level to the tops of the hills. In Vanua Levu I
found that these trees preferred the crests of wooded mountain-ridges or
the partially vegetated mountain peaks. They came under my notice in the
forests of the island of Fauro, in the Solomon Group, associated with
other large trees of the genera Canarium and Calophyllum.
Much interest is attached to the mode of dispersal of this genus, since
in some species the size of the drupes and of the included “stone” is so
great that, judged by those species only, it might be deemed impossible
to attribute the existence of the genus in isolated oceanic groups to
the agency of frugivorous birds. We are, however, compelled to appeal to
the bird, since, as my experiments in Fiji indicate, the genus has
little or no capacity for dispersal by currents, the “stone” when
containing a seed always sinking, whilst the entire fruit either sinks
at once or floats heavily for a few days.
The degree of fleshiness of the drupes of Elæocarpus varies in different
species, being sometimes slight and at other times pronounced, but,
speaking generally, they would be expected to attract frugivorous birds.
The colour of the fruits of some species is dark and purplish, whilst in
others it is a bright blue. In the last case the fruits are very
conspicuous and sappy. A Solomon Island species collected by me and a
Malayan species observed by Ridley had bright blue fruits, and Cheeseman
refers to the Rarotongan species as possessing fruits of this hue. Their
colour, therefore, would often aid in attracting birds, and we are not
surprised to learn that they form a favourite food with fruit-pigeons,
parrots, and other frugivorous birds in different regions. Amongst the
fruits found by Professor Moseley in the crops of fruit-pigeons in the
Admiralty Islands were those of Elæocarpus; whilst in the Solomon
Islands I noticed that the blue fruits of the “Toa,” a species of the
genus, were a favourite food of the same birds (_Bot. Chall. Exped_.,
iv. 307, 308; Guppy’s _Solomon Islands_, 293, 295). We learn also from
Hochstetter and from Sir W. Buller that the drupes of the “Hinau”
(Elæocarpus) form a favourite food of the parrots and fruit-pigeons of
New Zealand (Hochstetter’s _New Zealand_; Buller’s _Birds of New
Zealand_).
The question of size acquires considerable importance when we come to
consider the transport of the seeds of the genus to a group of islands
lying, like Hawaii, in the middle of the Pacific Ocean. The protection
of the seed is also another important matter. There can, however, be no
doubt that the hard woody or often osseous “stone” sufficiently protects
the seed. With regard to size, if we were to judge from the dimensions
of the fruits of some of the Fijian species, where, as I found, the
“stone” measures from 3 to 5 centimetres (1-1/4 to 2 inches) in length,
we might be led to form a very erroneous opinion of the capacity of the
genus for conveyance through the agency of frugivorous birds to Hawaii.
But when we turn to the Hawaiian species we find the difficulty much
diminished, though still serious, the fruits being smaller and
possessing a “stone” 2-1/2 centimetres or about an inch long. In other
regions, however, the genus may possess fruits yet smaller in size. The
Tongan endemic species, as described by Burkill, has fruits 1·7 cm. or
7/10 of an inch in length; and closely similar dimensions are given by
Kirk for a New Zealand species. In both these cases the “stone” would
not be more than half an inch or 1·2 cm. in length, and this would also
apply to the Solomon Island species above mentioned. In another New
Zealand species, where the drupe is only half an inch, the “stone” would
be still smaller. It is thus evident that the fruits of different
species vary greatly in size in different regions, and that there is no
difficulty in assuming that a small-fruited species could be dispersed
over the Pacific by frugivorous birds, and carried either to Hawaii or
New Zealand.
It might be an interesting point to determine to what extent a species
in an oceanic island could effect its own isolation by developing a
“stone” too large and too heavy to be transported across an ocean by
birds, such as seems to have happened with some Fijian species. But a
similar curious question is raised by the deterioration of a drupe in
its capacity for dispersal by frugivorous birds, when, as in the case of
the Hawaiian species of Elæocarpus, the drupes become dry and almost
sapless. As remarked in Note 68, this same feature is to be noticed in
the fruits of some of the Hawaiian endemic genera. This, of course,
would be quite in accord with what we should expect from the standpoint
of dispersal.
I will conclude these remarks on Elæocarpus with a reference to the
similarity of its distribution with that of Freycinetia. Both genera are
at home in the temperate rain-forests of New Zealand and in the tropical
rain-forests of the Pacific islands and of Malaya. Their capacities for
dispersal are so different and so unequal, the dispersal of Freycinetia
being seemingly so much more readily effected, that we can only suppose
that time has long since discounted any special advantage one genus
possesses over the other as regards distribution.
DODONÆA (Sapindaceæ).
This genus of small trees and shrubs includes between fifty and sixty
known species, of which about forty are confined to Australia; but a few
species are found over the tropical and subtropical regions of the
world, extending sometimes into temperate latitudes. There are, it
seems, only three species known from the oceanic groups of the tropical
Pacific: one, the cosmopolitan Dodonæa viscosa, that occurs in every
island of volcanic formation; and two others associated with it in the
Hawaiian Group, to which they are restricted. We have thus repeated in
this genus what is true of several other genera in Hawaii, such as
Metrosideros and Wikstrœmia, namely, the occurrence in that group of a
widely-ranging species accompanied by other species peculiar to those
islands. In the case of Dodonæa in Hawaii we should not expect to find
it very difficult to connect the endemic species with the widely-ranging
D. viscosa, which is a very variable species. The extreme forms in
different parts of the world are so different in character that Bentham
viewed this species as probably including the whole of the
extra-Australian species, excepting perhaps the Hawaiian endemic species
and one or two South African and Mexican plants (_Bot. Chall. Exped._,
iii. 136).
Of the two Hawaiian peculiar species, one, Dodonæa eriocarpa, is a
mountain shrub found in most of the large islands and occurring
sometimes at elevations of 6,000 to 8,000 feet. The other species, D.
stenoptera, is, according to Hillebrand, a very distinct species found
only on Molokai. Bentham was only acquainted with the first-named, and
his hesitation to include it as one of the innumerable forms of the
widely-ranging D. viscosa is very suggestive. However, whether or not
one or both of these peculiar forms are connected in their origin with
this species, it is certain that the genus has been established for ages
in Hawaii; and from D. viscosa we can learn how a species of the genus
can cross an ocean, and also how from a widely-ranging species
exhibiting extreme variability species peculiar to a group of islands
could have been derived.
The great variability of Dodonæa viscosa is associated with great
adaptability to different stations. Thus, as Mr. Hemsley tersely puts
it, it is one of those plants that thrive on the sea-coast as well as
inland, and in almost any soil or situation—provided, it may be added,
that the station is well exposed to the sun. Although Mr. Ridley
characterises it as a regular sea-shore plant in the Malay peninsula,
and although Prof. Schimper places it in the Indo-Malayan strand-flora,
it is as an inland plant that it is most characteristic of the Pacific
islands; and the key to its powers of adaptation to different stations
is to be found in its xerophilous habit. It is essentially a plant of
sunny places, and is equally at home on the parched inland plain, in the
open wood, on the sandy beach, on an old lava-field, or on rocky
declivities. It is not a plant of the rain-forest, preferring dryness to
humidity and sunshine to shade.
The following remarks on the mode of dispersal of the wide-ranging
Dodonæa viscosa will serve to roughly indicate the capacity of the genus
for distribution. It is a subject, however, that requires further
detailed investigation. The light, inflated, winged capsules of this
species, about an inch across, could be blown for long distances along
the ground and carried for short distances in the air by strong winds,
but, as is also remarked by Prof. Schimper (_Ind. Mal. Strand-flora_, p.
157), they are much too large to be transported by winds across a broad
tract of sea. The currents, however, may have aided in the dispersal of
the species in the case of island-groups 500 or 600 miles apart.
Although the membranous capsules before dehiscing would be unable to
withstand the “rough-and-tumble” of ocean-transport for more than a few
days, the seeds possess some floating powers of a purely accidental
nature due to the imperfect filling up of the seed-cavity in some of the
seeds. In an experiment made in Hawaii I found that only half the seeds
floated in sea-water. Prof. Schimper, in an experiment conducted in
Germany with seeds that must have been well dried by keeping, found that
they floated for from ten to sixty days. This limited capacity for
flotation might possibly allow the species to reach Tahiti by easy
stages from Fiji; but it is not sufficient to explain its occurrence in
the more isolated Hawaiian Group. The fruits and seeds of this plant
never, however, came under my notice in the floating or stranded
seed-drift of Fiji; and I am not inclined, for this and the reasons
above mentioned, to consider that the currents have been very effective
agents in dispersing this plant over the Pacific islands.
Hillebrand endeavoured to account for the wide distribution of Dodonæa
viscosa by “the glutinous capsules which would easily adhere to the
plumage of birds.” It may be here remarked that in the dried state
specimens of the plant have a varnished appearance as respecting the
leaves, branchlets, and capsules. In the living condition this is
represented by a glutinous or viscid condition of the surface of these
portions of the plant, rendering them adhesive to the touch. I found,
however, that only the immature capsules are markedly “sticky,” and that
in any case the adhesive power was quite insufficient to allow of
adherence for any length of time of fruits of this size to a bird’s
feathers. Mr. Ridley, who allows much latitude to birds in matters of
dispersal, remarks that the stickiness only appears when the specimen is
dry (_Trans. Linn. Soc. Bot._, 1888-94, p. 289). It is, nevertheless,
likely that the crustaceous seeds, which do not exceed 1/5 of an inch (5
mm.) in size, when swallowed by a bird granivorous in its diet, might be
voided unharmed, and the dispersal of the species assured. It is in this
fashion, I imagine, that the plant reached distant groups like Tahiti
and Hawaii.
There is, of course, the possibility that man has in past times aided in
the distribution of Dodonæa viscosa over the warmer regions of the
globe. But such an agency seems largely discounted in the case of an
isolated archipelago like Hawaii by the occurrence of endemic species.
Nor does the usual station in the Pacific islands support the view that
it was introduced by the aborigines. According to Hillebrand, it
possesses a variety (var. spathulata) in Hawaii which seems also to
occur in Tahiti and New Zealand. Nadeaud observes that in Tahiti it
grows as a bush on dry crests, and as a small tree, ten feet in height,
in the mountains.
Nor do the aboriginal names of Dodonæa viscosa point in the direction of
man’s agency. It possesses a different name in every group, and is
evidently not a plant with which the ancestors of the Polynesians were
familiar in the home of the race. Thus it is named “aalii” in Hawaii,
“apiri” in Tahiti, “ake” in Rarotonga, “lala vao” in Samoa, and I may
add “usi” or, as Seemann writes it, “wase” in Fiji.
Looking at these various facts, I am not inclined to exclude altogether
any one of the three agencies above discussed; but I should imagine
that, placed in their order of effectiveness, we should have first
birds, then the currents, and lastly man.
METROSIDEROS (Myrtaceæ)
Whilst this genus of trees and shrubs has its home in New Zealand and
Australia, there is an extremely variable Polynesian species,
Metrosideros polymorpha, ranging over all the volcanic groups of the
tropical Pacific, from Fiji to Pitcairn Island and from Hawaii to the
Kermadec group, but seemingly only in the Hawaiian group associated with
endemic species. According to the _Index Kewensis_ the genus comprises
about forty known species, of which two-thirds are confined to New
Zealand and Australia in equal proportions; whilst, among the rest, six
species belong to New Caledonia, two to Hawaii, and three to Malaya, and
there are solitary species in Chile, Madagascar, and South Africa.
I will attack the problem connected with the distribution of the genus
through the widely-ranging Polynesian species, Metrosideros polymorpha.
“This genus,” wrote Dr. Seemann, “is in a fair way of becoming in
Polynesia what Rubus is in Europe. It is very much given to variation,
and it is very difficult to find out the limits of the different
species.” In making these remarks he had this species in view, and his
adoption of Gaudichaud’s specific name of “polymorpha” to cover almost
all the Polynesian forms has been generally followed. Although so widely
distributed over the Pacific, it is in the Hawaiian Islands that this
tree attains its greatest development, growing gregariously and often
forming almost exclusively entire forests; and it is here that it
displays the greatest variation. But it was remarked by Seemann, and
this was confirmed by Hillebrand, that almost all the Hawaiian forms
occur in the Society or Tahitian Islands.
In connection with the great variability of Metrosideros polymorpha must
be considered its variety of stations and its great range in altitude.
Hillebrand describes seven Hawaiian forms of this species, and their
various stations and characters are well illustrated in his
descriptions. Thus, whilst the trees may attain a height of forty feet
in the forests, in elevated exposed situations they may be small and
gnarled or low and shrubby; whilst in the bogs and swamps of the high
levels of Maui and Kauai the plant grows as a prostrate shrub. It is not
at all unlikely that the two peculiar Hawaiian species of the genus had
a common origin from a widely-ranging species, which, if not the present
M. polymorpha, was its immediate ancestor. One of them was, indeed,
included by Dr. Seemann within the wide limits of this species, and the
other was accepted with a doubt.
To illustrate the great vertical range in the Hawaiian Group of
Metrosideros polymorpha, I will take it as I found it in the island of
Hawaii. Here it ranges from the coast up to about 8,000 feet above the
sea. But it is in the middle forest-zone at elevations of 2,000 to 4,000
feet, where it is often associated with the Koa and Olapa Trees (Acacia
koa and Cheirodendron Gaudichaudii), that it is most at home and attains
its greatest size. Higher up at heights of 5,000 to 7,000 feet in the
more open forests it is still in the company of the trees just named
together with Sophora chrysophylla and Myoporum sandwicense. At 8,000
feet it becomes very stunted and is accompanied usually by bushes of
Cyathodes and other plants of similar bushy growth. In the lower parts
of its range, from 2,000 down to 1,000 feet, it forms forests with the
Kukui Tree (Aleurites moluccana), mingled also with smaller trees such
as the Hawaiian Olive (Osmanthus), and the Kopiko (Straussia). Below
1,000 feet, and wherever bold promontories reach the coast and the
inland forest descends to the sea, we find it associated with such trees
and shrubs as the Lama (Maba sandwicensis) and different Akeas
(Wikstrœmia). On the partially vegetated surfaces of old lava-flows near
the coast it grows beside bushes of the Ulei (Osteomeles
anthyllidifolia) and of Cyathodes.
Compared with its behaviour in Hawaii, Metrosideros polymorpha takes a
relatively unimportant part in the vegetation of Fiji. As Horne
observes, the trees are most common in the dry parts of the two largest
islands and grow in the poorest soil. I found them in Vanua Levu usually
in open exposed situations, generally in the dry “talasinga” plains on
the north side of the island, where they were associated with Acacia
Richii, Dodonæa viscosa, and Casuarinas; and sometimes they occurred in
a shrubby form on the rocky peaks of the highest mountains. In Rarotonga
also, as we learn from Cheeseman, it is on the tops of the rocky peaks
and along the crests of the ridges that this species, which is abundant
in the island, is frequently found.
I may here allude to the curious fact observed by me on the upper open
wooded slopes of Mauna Kea at elevations of 6,000 to 7,000 feet, and
therefore on the outskirts of the true forest-zone. Here the Ohia Tree,
as the Hawaiians name Metrosideros polymorpha, often grows in close
association with the Olapa Tree (Cheirodendron Gaudichaudii). In one
locality, for instance, a large Olapa was growing in the fork of an Ohia
at about eight feet from the ground, and sending down roots on either
side. Sometimes the trunks of the Olapa and the Ohia were to be seen
growing in such close contact as to look like one tree. In one such case
a young tree, four feet high, of Myoporum sandwicense was growing in a
fork of the Ohia, whilst in a fork of the Olapa a plant of Vaccinium
penduliflorum, three or four feet in height, had established itself.
This remarkable instance of epiphytic growth also proved to be quite a
revelation with regard to the dispersal of seeds in this island. Amongst
these four associated plants, which include three trees and one shrub,
all except the Ohia, which was probably the original tree, have fruits
that would attract frugivorous birds; and in succession these birds had
first dropped a pyrene of the Olapa in the fork of the Ohia, and
afterwards the seeds of Myoporum again on the Ohia, whilst finally the
Vaccinium seeds were dropped into the fork of the Olapa after it had
developed into a tree.
The mode of dispersal of the seeds of Metrosideros polymorpha now
invites our attention. Since the fruits are dry, dehiscent capsules
possessing minute fusiform seeds, we are not able to appeal directly to
the agency of frugivorous birds to explain the wide dispersal of this
species. The seeds are light in weight and remind one a little of those
of the succulent fruits of Freycinetia. For purposes of dispersal,
however, they must be placed in the same category with other plants with
dry, dehiscent fruits and small seeds, such as the Vota (Geissois
ternata) of Fiji, a tree that in those islands grows in similar
stations. On a later page I have suggested that the seeds of the Vota
are dispersed by large bats that visit the trees for the sake of the
honey in the red flowers. With Metrosideros polymorpha birds act
probably in the same way. We are, in fact, informed by Mr. Perkins that
the nectar-feeding birds of the Hawaiian Drepanids now obtain their main
supply of this food from the blossoms of this tree. If bats or birds
visit the large red flowers of Metrosideros polymorpha for the same
purpose, it is not difficult to imagine that they might carry away in
their fur or in their plumage some of the small seeds shaken out of old
dehiscent capsules. In this connection we may note that the Kaka Parrot
(Nestor meridionalis) of New Zealand is said to feed largely on the
scarlet blossoms and nectar of Metrosideros robusta (Evans’ _Birds_, p.
374).
The seeds of Metrosideros polymorpha might no doubt be carried by winds
from one mountain-top to another and across narrow straits, but only
whilst adherent to a bat or a bird could they be carried across a wide
tract of ocean. Speaking of the genera Metrosideros and Lobelia in
connection with their occurrence in the Kermadec Islands, Sir J. Hooker
long ago referred to their minute seeds as not adapted for transport
across oceans unless their minuteness and number fitted them for it
(_Journ. Linn. Soc._, i. 127). The point that is raised here for these
genera in the Kermadec Group can be raised for the same two genera in
Hawaii and for a multitude of other small-seeded genera in those
islands.
ALYXIA (Apocynaceæ).
This genus of climbing or straggling shrubs tells its own story of the
widely dispersed Indo-Malayan genera in the Pacific islands. Containing
about forty known species, it is distributed over the tropical regions
from Madagascar and the Mascarene Islands eastward to the Paumotu Group
and Pitcairn Island in mid-Pacific, and has its focus in the area
comprised by Malaya, Australia, and New Caledonia. In the _Index
Kewensis_ about eight species are assigned to New Caledonia, seven to
Australia, and seven to Malaya. One species, Alyxia stellata, ranges
over nearly the whole of the area of the genus from tropical Asia,
through Malaya, across the South Pacific to Tahiti. It will be for the
future investigator to determine how far the present distribution of the
genus can be connected with one or two widely-ranging polymorphous
species. The data at my disposal seem to show that in the open Pacific,
at all events, the history of the genus has gone a step beyond this
stage.
Of the seven or eight species recorded from the Pacific islands east of
New Caledonia, only two or three seem to be now recognised as restricted
to particular groups, namely, one in Hawaii (Schumann), one in Fiji, and
one in Rarotonga. The other species indirectly connect together all the
groups, although no single species occurs over the whole region. Thus
the Hawaiian species, Alyxia olivæformis (Gaud.) has in recent years
been found in Upolu, in the Samoan Group, by Dr. Reinecke, an
exceedingly interesting though unusual specific link between these two
archipelagoes. Two species, A. stellata and A. scandens, range over the
South Pacific from Fiji to Tahiti, the last-named also occurring in the
Paumotu or Low Archipelago; whilst Rarotonga possesses a form closely
allied to the first-named, and to it Cheeseman has given specific rank.
Another species, A. bracteolosa, links together the contiguous Fijian,
Tongan, and Samoan groups. This distribution is what we should have
expected if one or two polymorphous species had originally ranged over
the Pacific and were advancing towards that stage of differentiation
when each group possesses its own peculiar species. (It may be here
remarked that an undetermined species of Alyxia is accredited by Maiden
to Pitcairn Island, which indicates that the genus has extended east in
the Pacific almost as far as the extreme limit of the Polynesian
region.—_Australas. Assoc. Reports_, Melb., 1901, viii.)
All visitors to these islands that are interested in their floras will
be familiar with the Alyxias; and there are few of their plants that the
natives take more pleasure in pointing out to white men. They are
readily recognised on account of their black moniliform drupes and their
milky sap. All over Polynesia, whether in Hawaii, Tahiti, Samoa, or
Fiji, the aborigines value the plants on account of the delicate
fragrance of their foliage and bark. These materials they use for
personal decoration and in making wreaths, stripping off the bark of the
young branches with their teeth in the same fashion in Fiji and Hawaii
and probably in all the Pacific islands. Throughout Polynesia, excluding
Fiji, they bear the same name, which takes the form of “maile” in Hawaii
and Samoa, and of “maire” in Tahiti and Rarotonga—a name which the
Maoris, remembering the Alyxias of their tropical home in the South
Pacific, have applied to New Zealand species of Olea and Eugenia. The
Fijian generic name for Alyxia is “vono.”
A word may be said about the station of these plants in the Pacific
islands. In Hawaii they occur in the middle and lower forests, and
usually between 2,000 and 4,000 feet in elevation. In Tahiti they
frequent the crests and precipitous rocky slopes of the mountains at
elevations of from 3,000 to over 6,000 feet. The Rarotongan species
often forms extensive thickets in rocky localities on the hills. In
Samoa they are found usually in the mountain forests. In Fiji they grow
on the outskirts of the virgin forests and on rocky sparingly vegetated
mountain peaks. I found them often in Vanua Levu growing amongst the
open vegetation on the summits of isolated mountains at elevations of
2,000 to 2,500 feet, where they were associated with other plants like
Elæocarpus, Pleiosmilax, and Scævola, possessing similar fleshy fruits
likely to be dispersed by frugivorous birds.
The Alyxias indeed seem well suited for dispersal by birds. The black
fleshy drupes would readily attract them; and the solitary seed
protected by a very tough horny albumen might be ejected unharmed in
their droppings.
--------------
It would be possible to enter into similar detail with several other
genera of this period; but here I can only direct attention to their
principal indications, permitting myself a little more license when
discussing the means of dispersal.
ALPHITONIA (Rhamnaceæ).—Amongst other genera with polymorphous species
closely following the lines taken by Metrosideros in the Pacific is
Alphitonia, a small Malayan and Polynesian genus of tall trees,
containing at most three or four species, one of which (A. excelsa) has
almost the range of the genus and is found in most of the Pacific
archipelagoes. So variable is this widely-ranging tree that Bentham
suggested that there was only one species in the genus (_Bot. Chall.
Exped._, iii. 133), a suggestion especially interesting in connection
with the _rôle_ taken by polymorphous species in the Pacific. As bearing
on the mode of dispersal of this species, it may be observed that my
Fijian experiments show that the fruits are not fit for transport by
currents. With the mature drupe the outer coverings become pulverulent,
and the fruit breaks down, freeing the pyrenes which do not float; nor
have the seeds any buoyancy. Although the dry drupes would seem
unattractive to birds, it is to birds we must look for the dispersal of
the genus.
PISONIA (Nyctagineæ).—Like Dodonæa, Metrosideros, and Alphitonia, the
cosmopolitan genus Pisonia possesses a polymorphous species that
displays its variation in every Pacific group and occupies a
considerable number of stations. The earlier botanists in the Pacific
differed much as to the species of this region, and this led Mr. Hemsley
to observe in his paper on the Tongan flora that it is difficult to
understand the various Polynesian and Australian species except on the
assumption that there is one very variable species. Recognising this
difficulty, Drake del Castillo deals somewhat summarily with nearly all
these forms, uniting them under one comprehensive species, P.
umbellifera (Seem.), thus constituting “une espèce très-polymorphe” that
ranges (generally in maritime districts) over tropical Asia and the
islands of the Indian and Pacific Oceans, extending to North-East
Australia and to New Zealand. On account of the unusual capacity for
dispersal possessed by this species—a subject to be immediately
discussed—the tendency to specific differentiation has been kept in
check, though the process has gone farther in some groups than in
others, as in the case of Hawaii, where Hillebrand’s endemic species
has, however, been included by Drake del Castillo in his polymorphous
species, P. umbellifera.
The fruits of this genus possess no capacity for dispersal by currents.
They never came under my notice either in floating or stranded
seed-drift, and have little or no buoyancy. Prof. Schimper,
experimenting on the well-dried fruits of Pisonia aculeata, a seaside
shrub common in America and in the Old World, and destined probably to
be brought by the systematist into touch with the polymorphous P.
umbellifera, found that they sank in a day or two (_Ind. Mal.
Strand-flora_, p. 156). Dismissing the agency of the current, he looked
to that of the bird for the explanation of the dispersal. The
probability of the effectiveness of this last-named agency has long been
surmised. It attracted the notice of Darwin and especially invited the
attention of another student of plant-dispersal, Dr. H. O. Forbes. The
long, narrow, often fusiform fruits are invested by a somewhat
coriaceous perigone and range from less than an inch to three inches in
length (2-7·5 cm.). They excrete a very viscid fluid often in quantity,
and sometimes also possess glandular spines. The Hawaiians, according to
Hillebrand, used this material as bird-lime for catching birds, and the
fruits, he says, will stick fast to the paper in the herbarium for
years. In that group I often found the fruit adhering firmly to my
clothes. Writing of these trees on Keeling Atoll, Forbes observes that
their sticky fruits are often such a pest to birds roosting in their
branches that they have proved fatal to herons and boobies by collecting
in their plumage. “It is easy to perceive,” he remarks, “how widely this
tree might be disseminated by the birds that roost on it” (_The Eastern
Archipelago_, p. 30). In New Zealand, as we learn from Kirk, the viscid
fruits of Pisonia brunoniana attract small birds which become firmly
caught and die miserably. A cat has been known to wait under a tree
watching its opportunity of preying on the entangled birds. Sir W.
Buller states that the New Zealand fruit-pigeon feeds at times on the
green fruits of P. umbellifera; and we can infer that it occasionally
carries off some of the riper fruits in its feathers.
WIKSTRŒMIA (Thymelæaceæ).—This is a small genus of shrubs and small
trees, with red or yellowish drupes fitted for dispersal by frugivorous
birds, that is confined mainly to tropical Asia, Australia, and
Polynesia. Following Seemann and Drake del Castillo, we may say, that
like several other genera of this period, this genus possesses in the
tropical Pacific a widely-ranging species, W. indica, that occurs in
Hawaii, the Marquesas, Tahiti, Samoa, and Fiji, growing amongst the
vegetation immediately behind the beaches and in the plains and open
wooded districts inland. In Hawaii it is associated with half a dozen
peculiar species, and in Tonga there is also an endemic species. The
widely-ranging species has its home in the Indian Archipelago and in the
Asiatic mainland, and occurs also in Australia. According to Gray, the
American botanist, it is represented by a different variety in almost
every group in the tropical Pacific, and it presents us therefore with
another example of a polymorphous species which links Polynesia directly
with Malaya. As bearing on the dispersal of the genus by birds, it may
be added that Mr. Perkins in the _Fauna Hawaiiensis_ speaks of some of
the Drepanids and of a species of Phaeornis as feeding at times on the
fruits of these plants.
PEPEROMIA (Piperaceæ).—All observers of tropical plant-life will be
familiar with this genus of low herbs growing on tree-trunks, on the
soil, on rocks, and on stonewalls, and comprising about 500 known
species distributed over the warmer regions of the globe and sometimes
extending into cooler latitudes. In Polynesia it attains its greatest
development in Hawaii, where Hillebrand enumerates about twenty species,
of which, after excluding doubtful forms, at least a third must be
endemic. Tahiti, Samoa, and Fiji are each known to possess three or four
species, of which one is usually restricted to the group. Two species,
P. reflexa and P. leptostachya, link together nearly all the groups of
the tropical Pacific, including Hawaii, the first cosmopolitan, and the
second hailing from North-East Australia and indicating that the genus
has entered Polynesia from the west.... These plants possess spikes of
small berries containing a single seed, and are evidently, like other
Piperaceæ, dispersed by frugivorous birds. It is to be noted that the
presence of a West Indian and Mexican species in the Bermudian caves is
attributed by Mr. Hemsley to frugivorous birds (_Bot. Chall. Exped._,
Introd. 49, i. 62). In Vanua Levu they occur on the bare rocky peaks of
some of the mountains under such conditions that the seeds could only
have been brought by birds. Thus, on the bare surface of a large block
of tuff forming the highest peak of Koro-Mbasanga, 2,500 feet above the
sea, I found only two plants, Oxalis corniculata and a species of
Peperomia.
EUGENIA (Myrtaceæ).—This is a very extensive genus split up into
different subgenera, and comprising some 600 or 700 known species
scattered over the warm regions of the globe. Their fleshy, usually red,
berries contain as a rule one or two large seeds, and attract birds and
animals of all descriptions. The feature most interesting to us is the
dispersal of the genus over the Pacific islands eastward to the Low
Archipelago and northward to Hawaii. The track by which it has entered
the Pacific from the west is indicated in the distribution of the
species. The genus is only well represented in the Western Pacific,
whilst eastward and northward of Samoa and Tonga the distribution is
fitful and irregular, it being evident that the extension beyond these
two groups has been accomplished with difficulty.
There are at least twenty-five species in Fiji, of which perhaps half
would be peculiar; in Tonga eight species, of which two may be endemic;
in Samoa thirteen species, of which four are peculiar; in Rarotonga
none; in Tahiti a single non-endemic species; and in Hawaii two species,
of which one is peculiar. Only truly indigenous species are here
recorded, and Eugenia malaccensis, which has accompanied the aborigines
in their migrations, is not included. A solitary species, E. rariflora,
connects together all the principal archipelagoes from Fiji to Tahiti
and the Gambier Islands, and northward to Hawaii. Nine species are known
to be common to the region in which lie the three groups of Fiji, Tonga,
and Samoa; and since some of these species occur in the groups further
west they may be regarded as keeping up the connection with the original
home of their ancestors in the Malayan region.
Looking at these facts of distribution of the genus Eugenia in the open
Pacific, it is evident that whatever dispersal of the genus is now in
progress in this ocean is mainly confined to an interchange between the
groups of Fiji, Tonga, and Samoa in the Western Pacific, and doubtless
between the islands further west of these groups. The smaller islands
lying between and around these three groups participate in the
distribution of the species common to all. Thus Wallis Island, according
to Drake del Castillo, possesses two of these species. Over the rest of
the ocean the dispersal of the genus seems to be no longer effective,
since Eugenia rariflora, which links together Fiji, Tahiti, and Hawaii,
shows signs of differentiation in nearly every group. In Hawaii, where
it is very rare and is only recorded from two of the islands, it has
developed a small-leaved variety. In Tahiti it displays the same
variation; and Seemann observes that there are differences between the
Tahitian and Fijian species which may be almost specific in value. It
would also appear that both in Hawaii and Tahiti the fruits have become
less attractive to birds, being described as “dryish” and “dry,” which
is, as Dr. Seemann remarks, certainly not true of the Fijian plant.
In Fiji the Eugenias, as small trees and shrubs, find their home usually
on the banks of streams and rivers, on the outskirts of forests, and
occasionally at the coast. One of them, E. richii (Gray), is a
characteristic littoral tree in the group. A tree near it in character
was found by me of common occurrence in the interior of coral islets in
the Solomon Group (_Solomon Islands_, p. 297). E. rariflora occurs also
in the interior of coral islets in Fiji and amongst the vegetation at
the back of the mangrove-swamps.
Coming to the mode of dispersal of the genus in the Pacific, I may
remark that all the species, with the doubtful exception of the Fijian
and Samoan Eugenia neurocalyx (the Lemba of Fiji), are wild trees and
shrubs useless to man, but much appreciated by pigeons, pigs, &c., on
account of their fleshy fruits. Since exact observations on the
possibility of their dispersal by currents seemed to be wanting, I made
some experiments in Fiji. Out of six species, which included E.
corynocarpa, rariflora, richii, and rivularis, the mature fruits of most
species sank in sea-water in from seven to ten days. However, those of
the beach tree, E. richii, floated for a fortnight. The cause of sinking
in all cases lay in the decay of the outer fleshy covering. As I have
observed in river and sea drift, fish bite at the floating fruits, and
in this manner the seeds would soon be liberated and sink. The seeds of
all the plants sank at once in my experiments except with one species,
where the seed loosely filled its test and thus a floating-power of a
few days was acquired. Currents, it is apparent, could never account for
the dispersal of the genus over a broad extent of ocean, though in a few
cases, as in that of the littoral tree above noted, it is quite possible
that the fruits could be successfully transported across a tract of sea
200 or 300 miles in width.
It has long been known that fruit-pigeons are fond of the fruits of wild
species of Eugenia, and I found the Solomon Islanders and the Fijians
well acquainted with the fact. The fruits of a tall Eugenia tree, near
E. richii, common in the interior of the coral islets of Bougainville
Straits in the Solomon Group, were found by me in quantities in the
crops of fruit-pigeons shot by Lieut. Heming and Lieut. Leeper on the
islets (_Solomon Islands_, pp. 293, 297; _Bot. Chall. Exped._, Introd.
46, iv. 312). Dr. Seemann remarks that in Fiji the red fruits of E.
brackenridgei are eaten by pigeons. The somewhat thin coverings of the
seeds of this genus would seem to offer but a slight protection in a
bird’s stomach, though in one species the test was almost crustaceous.
Most species possessed only one or two large seeds in each fruit, though
this number may vary in the same individual. Thus, out of ten fruits of
Eugenia rariflora in Fiji, six had one seed, three had two seeds, and
one had three seeds. In the fruit of E. neurocalyx, however, the seeds
range from three to five.
It is the question of size that is of importance in considering the
possibility of birds transporting the seeds over a broad tract of ocean.
Eugenia rariflora, the species found all over the Pacific, has seeds
that measure in the Fijian plant one-fourth to one-third of an inch (6
to 8 mm.) across; and in Hawaii, according to Hillebrand, they would
perhaps be rather smaller. In point of size there is less difficulty
with regard to the transport by birds across the ocean to Hawaii of the
seeds of Eugenia rariflora than with the “stones” and seeds of some
other genera, like Elæocarpus, Osmanthus, and Sideroxylon, that must
have been conveyed there by the same agency. The fruits of several of
the Fijian species are of the size of a large cherry; but it is
noteworthy that in those species like E. corynocarpa and E. neurocalyx,
where the fruits are large and the seeds about an inch in size, the
plants are confined to the Western Pacific only, namely, to the
Fiji-Samoa region.
There is therefore no difficulty, from the standpoint of size, in
accounting for the distribution by birds of the widely-ranging Eugenia
rariflora over Polynesia; but at first sight there seems to be a real
difficulty with regard to the protective coverings of the seed. Yet
Nature speaks with no hesitating voice in the matter. The West Indian
and Florida species, E. monticola, regarded as indigenous in the
Bermudas, must have reached that group through the agency of birds that
carried its seeds over quite 800 or 900 miles of sea; and it may here be
noted that South Trinidad, lying some 600 miles off the coast of Brazil,
and Rodriguez, distant about 330 miles from Mauritius, each possess
species (_Bot. Chall. Exped._, Introd., 12, i. 32, ii. 128). If
fruit-pigeons can transport Eugenia seeds across 600 or 800 miles of
ocean, there would be no difficulty in accounting for the stocking of
the Fijian, Tongan, and Samoan Islands with the genus from regions to
the west. But the occurrence of the genus in Hawaii seems to compel us
to assume that the seeds have been carried in a bird’s stomach over
1,500 to 2,000 miles of ocean. This difficulty, however, does not really
exist. Eugenia rariflora, the Polynesian species found in Hawaii,
frequents, as before observed, coast districts and coral islets in Fiji,
and if we suppose that the low islands of the Fanning and Phœnix Groups,
lying between Hawaii and Samoa, have served as stepping-stones, a
capacity of crossing 1,000 miles of ocean would be alone required. This
is not much in excess of the distance that must have been traversed by
the bird that first brought the seeds of Eugenia monticola to the
Bermudas.
Other genera like Morinda and Scævola, possessing fleshy fruits
dispersed by frugivorous birds, have been mentioned in different
connections in other parts of this work, and will not be further dealt
with here. But before concluding this chapter I will refer briefly to
one of the disquieting mysteries in the flora of the Pacific which is
presented to us in the genus Gossypium. Three species are, or were,
truly indigenous in this region. One is Gossypium drynarioides, a small
endemic tree found by Nelson, the companion of Captain Cook, in Hawaii,
which was very rare in Hillebrand’s time, and is perhaps now extinct.
The second is G. tomentosum (Nuttall), which is also peculiar to Hawaii,
where it is found on the beaches. I am following here the _Index
Kewensis_; but it should be remarked that this species occurs also in
Fiji, though Seemann regards it as introduced. The third is G.
religiosum (L.), found by Captain Cook’s botanists growing wild in
Tahiti, and hailing from the tropics of the Old World. The seeds of the
first species are covered with a short brownish tomentum, and could
never have been of any value. The tawny wool of the seeds of the second
species has a staple too short for cultivation; whilst the Tahitians do
not seem to have made any use of the third species. It is difficult to
draw any conclusion concerning the presence of these plants in the
Pacific islands at the time of their discovery; nor can Dr. Seemann, who
was especially well informed in these matters, aid us much in our
endeavours to solve the mystery. From the aboriginal names we get no
clue. The Hawaiian name of “huluhulu” seemingly refers to the hairy
covering of the seed; whilst the Tahitian “vavai” and “ovari” simulate
the Fijian “vauvau,” which is merely the reduplicated form of “vau” (the
word in many shapes for Hibiscus tiliaceus in Malaya and Polynesia), and
is applied by the Fijians to Hibiscus esculentus and to the introduced
species of Gossypium.
When in Hawaii I ascertained that neither the seeds of the littoral
plant, Gossypium tomentosum, nor those of two cultivated species
possessed any fitness for dispersal by the currents, the scraped seeds
sinking at once, whilst when covered with the wool they floated only for
a few days. Further references to G. tomentosum in Hawaii are given in
the index of this volume.
_The Last Stage of the General Dispersal of Plants of the Malayan Era._
We arrive now at the close of the era of the general dispersal of
tropical plants, mainly Malayan, over the Pacific, and this brings us
down to our own age. The few genera that are still dispersed have no
peculiar species in particular groups. The species which often range
over all the groups, and retain as a rule their characters in most of
them, do not therefore display, except in a few cases, that extreme
variation which would give them a place in the ranks of the polymorphous
species. The dispersing agencies, in fact, are sufficiently active to
check marked variations, and the process of isolation has scarcely
begun.
We perceive the reason of this when we look at the nine genera which are
taken as samples of this period, viz., Rhus, Osteomeles, Viscum,
Plectronia, Boerhaavia, Polygonum, Pipturus, Boehmeria, and Dianella,
most of them being known to be dispersed by birds at the present day.
Six of the genera possess fruits likely to attract frugivorous birds;
whilst one of them, Boerhaavia, has sticky fruits that would be apt to
adhere to plumage. Actual observations in the cases of Rhus, Viscum, and
Plectronia establish the fact of their dispersal by fruit-eating birds;
and there is no difficulty in postulating the same agency for
Osteomeles, Pipturus, and Dianella. A method by which Boerhaavia fruits
would be transported in the plumage of birds has been observed by Mr.
Lister; whilst the nutlets of Polygonum are known to afford food to a
variety of birds and to be thus distributed.
In this period the plants all hail from the Asiatic side of the Pacific.
Three of the genera, Plectronia, Pipturus, and Dianella, belong almost
exclusively to the Old World. Five occur in both the Old and New Worlds,
but, as with Rhus, Viscum, Boerhaavia, and Boehmeria, are represented by
Old World species in the Pacific, or, as with Polygonum, possess a
cosmopolitan species (P. glabrum) ranging over the warm regions of the
globe. Even Osteomeles presents no exception to the rule, since the
Pacific plant is the only one of its species that is not American.
We have in Polygonum glabrum the only aquatic or semi-aquatic plant
widely distributed over the Pacific islands that can lay claim in all
groups to be indigenous. It is associated in Hawaii with species of
Potamogeton and Naias, aquatic genera that have, however, a limited
distribution in Polynesia.
I will now make a few remarks on each genus such as bear on their
distribution and on their mode of dispersal in the Pacific.
RHUS (Anacardiaceæ).—The representation of this genus by indigenous
species in oceanic islands not only in the Pacific but also in the
Atlantic, as in the Bermudas, is of especial interest in connection with
dispersal by frugivorous birds, since the drupes are typically dryish
and might appear to be not very attractive to birds. There are two Old
World species known from the Pacific islands: one being R. simarubæfolia
(Gray), distributed over the South Pacific groups from Fiji to Tahiti
and hailing from Malaya; the other, R. semialata (Murray), alone
recorded from the Hawaiian Group and derived probably from China or
Japan. This indication that the groups of the North and South Pacific
have derived their species, the first from Temperate Asia and the second
from Tropical Asia, is of some interest. In Samoa, according to
Reinecke, the fruits of R. simarubæfolia, which are of the size of a
pea, form the favourite food of the fruit-pigeons. That birds disperse
the seeds of the various Sumachs is familiarly known. In the United
States, as we learn from Barrows, Beal, and Weed, crows, woodpeckers,
and other birds feed extensively in winter on the fruits of different
species of Rhus, including the Poison Ivy (R. toxicodendron). The crows
discharge the seeds in pellets after retaining them for about thirty
minutes. Some seeds we must infer would pass into the intestines, where
they might be retained for ten to twelve hours (see Chapter XXXIII.),
which would be long enough, according to Gätke’s views of bird-velocity,
to enable them to be transported over a thousand miles of ocean.
OSTEOMELES (Rosaceæ).—One of the most interesting cases of dispersal in
recent times over the Pacific islands is that of O. anthyllidifolia. Of
the ten known species of the genus, nine are confined to South America;
whilst the Pacific species, which is not recorded from America, has been
found in Upper Burma, Japan, the Liukiu and Bonin Groups, Hawaii,
Pitcairn Island, Mangaia, and Rarotonga. The remarkable distribution of
the Pacific plant at once attracts attention. I was very familiar with
it in Hawaii, where it forms one of the commonest bushes in open-wooded
and thinly vegetated districts at elevations usually ranging from the
coast to 3,000 feet. Its small, white, somewhat fleshy fruits would
attract birds, and the hard pyrenes would be able to pass unharmed
through a bird’s digestive canal. It seems probable that, like Rhus
semialata, this plant entered the Pacific Ocean from the north-west,
taking the route by Japan and the Bonin Islands, and following the trend
of the archipelagoes over Polynesia (see _Bot. Chall. Exped._, Introd.
p. 18; _Journ. Linn. Soc. Bot._, vol. 28, 1891, &c.).
VISCUM (Loranthaceæ).—A single species, V. articulatum, which has its
home in Southern Asia, is found in most of the Pacific groups, such as
Hawaii, Marquesas, Tahiti, Rarotonga, Fiji, &c. The dispersal of the
genus by frugivorous birds is well known.
PLECTRONIA (Rubiaceæ).—I have found it more convenient to place this
genus here, although there are probably one or two species peculiar to
Fiji. This genus of shrubs, which is spread over the warm regions of the
Old World, is represented by two widely distributed species in
Polynesia, Plectronia odorata (B. and H.) and P. barbata (B. and H.),
the first alone extending to Hawaii. I was very familiar with P. odorata
in Hawaii and was much interested in its mode of dispersal, since the
species has also been found in Fiji, Tahiti, the Marquesas, and Pitcairn
Island (Maiden). In one locality, where an old lava-field was partially
covered by its bushes then in fruit, the doves were feeding greedily on
the drupes, the “stones” of which, as well as the partially digested
fruits, were to be seen in quantity in their excrement near a
water-hole. The stones are very hard and about a third of an inch (8
mm.) in length, and are exceedingly well suited for transport by
frugivorous birds. It was very probably to one of these species of
Plectronia that Peale alluded when he wrote of the berries of a species
of Canthium forming the principal food, on one of the Paumotu Islands,
of Numenius tahitensis, a curlew that has its home in Alaska, migrating
south in autumn to Hawaii, Tahiti, and the Paumotu Group (Wilson’s AVES
HAWAIIENSES).
BOERHAAVIA (Nyctagineæ).—Two or three Asiatic species of this genus, B.
diffusa, B. tetranda, &c., are spread all over the Pacific islands from
the Fijis to the Paumotus and northward to Hawaii. Similar or allied
species occur on the coral islands of the Indian Ocean, as on Diego
Garcia and on Keeling Atoll. Though these plants have often been
accidentally spread by man with his cultivated plants, it is probable
that sea-birds have regularly aided in their dispersal. The fruits, on
account of their small size and their glutinous sticky surfaces, are
well suited for transport in a bird’s feathers. Mr. Lister, as quoted by
Hedley (from _Proc. Zoolog. Soc._, 1891), made an interesting note in
this connection on one of the islands of the Phœnix Group, where he
found a fruit of Boerhaavia tetrandra entangled in some of the down that
had been preened by a booby (Sula piscatrix) out of its feathers whilst
roosting in a clump of Tournefortia trees.
POLYGONUM (Polygonaceæ).—This genus is represented by the cosmopolitan
Polygonum glabrum, the only aquatic or semi-aquatic plant that is
generally distributed in the Pacific islands. It occurs in fresh-water
swamps and beside streams and ponds in Tahiti, Tonga, Fiji, Hawaii, &c.,
and was gathered by Banks and Solander when Captain Cook first visited
Tahiti. That this plant has been distributed by geese, ducks, and
waterfowl over the tropics of the globe can scarcely be doubted. In
England I have found the nutlets of Polygonum convolvulus, P.
persicaria, and P. aviculare in the stomachs of a wild duck and a
curlew; and they came frequently under my notice in the crops and
intestines of different kinds of partridges and of wood-pigeons. Though
most of the fruits were generally injured, a few of them were not
uncommonly obtained in a sound condition.
PIPTURUS (Urticaceæ).—This is a genus of small trees and shrubs found in
the Mascarene Islands, Malaya, Australia, New Zealand, and throughout
Polynesia. Besides P. albidus, which is confined to Hawaii and Tahiti,
there are two Malayan species, P. argenteus and P. velutinus, which are
widely distributed over the islands of the South Pacific, extending to
Tahiti and the Marquesas. The fleshy receptacle and small achenes of the
compound fruit of Pipturus give it the appearance of a white immature
strawberry, and as such it would be likely to attract frugivorous birds.
Plants of this genus are included amongst the numerous plants from the
bast of which the natives used to prepare their native cloth or from
which they obtained the fibres for their fishing-lines.
BŒHMERIA (Urticaceæ).—There is an Asiatic species widely spread in the
South Pacific and another closely-allied species in Hawaii; but I
possess no data relating to the dispersal of the genus. The fruits are
dry and consist of an achene in a persistent perianth.
DIANELLA (Liliaceæ).—This is a genus of herbs, possessing often pretty
blue berries, that extends over tropical Africa, tropical Asia, the
Mascarene Islands, Malaya, Australia, and New Zealand, and is found in
all the larger Pacific archipelagoes. Of the twelve species named in the
_Index Kewensis_ only two belong to America, occurring respectively in
Cuba and Venezuela. There are two species in the islands of the tropical
Pacific: (_a_) Dianella ensifolia, found in Hawaii and ranging over the
Mascarene Islands, India, China, Malaya, and tropical Australia; and
(_b_) D. intermedia, recorded from most of the groups of the South
Pacific (Fiji, Tonga, Rarotonga, Tahiti), and occurring also in Norfolk
Island and New Zealand. These two plants occur in similar stations all
over Polynesia, sometimes growing in the grassy plains on the dry side
of an island, at other times extending up the thinly wooded mountain
slopes and reaching the hill-crests some 2,000 or 3,000 feet above the
sea. Their berries would readily attract birds; and their seeds, about
one-fifth of an inch (5 mm.) in size in the case of D. ensifolia, could
be carried uninjured in the stomach and intestines of a bird.
_Summary._
(1) A later period in the era of the general dispersal of Malayan plants
over the Pacific is indicated by the genera that contain species found
outside each group as well as species restricted to it.
(2) In this period the extremely variable or polymorphous species plays
a conspicuous part, as represented in such genera as Alphitonia,
Dodonæa, Metrosideros, Pisonia, and Wikstrœmia.
(3) The first stage is displayed by a solitary widely-ranging species
found over most of the Polynesian archipelagoes, and varying
independently in every group.
(4) The next stage is shown where the polymorphous species, having done
its work of distributing the genus, ceases to wander and settles down
and “differentiates” in all the groups; and the genus thus includes both
peculiar and widely-ranging species in each group. Most of the genera
possessing polymorphous species are in this stage.
(5) The following stage is displayed by those genera like Elæocarpus,
Eugenia, and Peperomia, where peculiar species are especially developed
in particular groups, and we get subcentres of distribution for the
genus, that is to say, small gatherings of peculiar species. A few
species, however, still keep up a connection with neighbouring
island-groups. Should this be severed we get the type of genus belonging
to the earlier period of the Malayan era as described in the preceding
chapter, a genus possessing only peculiar species and destined, after
ages of further isolation through the failure of the dispersing
agencies, to give rise to a new generic type or types.
(6) Frugivorous birds were chiefly active in dispersing these genera
over the Pacific. Some of the genera possess seeds or “stones” of such a
size that at first sight their transport by frugivorous birds to Hawaii
seems improbable; but, as in the case of Elæocarpus, it is shown that
this difficulty does not apply to all species of a genus, some of them
having much smaller seeds or stones.
(7) The close of the era of the general dispersal of Malayan plants over
the Polynesian Islands is indicated by those genera that are represented
more or less entirely by widely ranging species. Though such species may
vary among the different groups, they rarely take the rank of
polymorphous species, the agencies of dispersal being sufficiently
active to check marked variations.
(8) Several of the genera of this concluding stage, like Rhus, Viscum,
and Plectronia, are known to be dispersed by frugivorous birds, whilst
others, like Osteomeles and Dianella, are equally well suited for this
mode of dispersal.
(9) Distinct indications are afforded by the genera Rhus, Osteomeles,
and Dianella that the Hawaiian Group has been often supplied with its
plants directly from the Old World by the Asiatic mainland, whilst the
groups of the South Pacific have received different species of the same
genus by Malaya and tropical Australia.
CHAPTER XXVII
THE MALAYAN ERA OF THE NON-ENDEMIC GENERA OF FLOWERING PLANTS
(_continued_)
THE AGE OF LOCAL DISPERSAL
_Synopsis of the Chapter._
HAWAII.—(1) _The Hawaiian residual genera, being those not found in
either the Fijian or the Tahitian regions._ The genera especially
discussed are Osmanthus, Sicyos, Jacquemontia, Cuscuta, Rumex,
Dracæna, Naias, Potamogeton; and amongst others mentioned are
Perrottetia and Embelia.
(2) _The Hawaiian genera found in Tahiti and not in Fiji._ Very few,
and illustrated by Byronia, Reynoldsia or Trevesia, Phyllostegia, and
Pseudomorus, though it is likely that most of these will be
subsequently discovered in Fiji.
(3) _The Hawaiian genera found in Fiji and not in Tahiti._ Illustrated
by Eurya, Gouania, Maba, Sideroxylon, Antidesma, Pleiosmilax, Ruppia.
(4) _The absentees from Hawaii._ Illustrated amongst the orders by the
Sterculiaceæ (see text), the Meliaceæ, the Rhizophoreæ, the
Melastomaceæ, and the Coniferæ, and amongst the genera by
Trichospermum Loranthus, Stylocoryne, Ophiorrhiza, Alstonia, Hoya,
Ficus; and a great many others might be cited.
TAHITI.—(1) _The Tahitian residual genera._ Only six in number—Cratæva,
Buettneria, Berrya, Coriaria, Bidens, Lepinia.
(2) _The Tahitian genera found in Hawaii and not in Fiji._ See above
under (2).
(3) _The Tahitian genera found in Fiji and not in Hawaii._ (a) Those
possessing only species confined to the Tahitian region or to East
Polynesia, of which Meryta, Ophiorrhiza, Alstonia, and Loranthus are
examples.
(b) Those possessing widely-ranging species besides, often, species
confined to the Tahitian region, such as Grewia, Nelitris, Melastoma,
Randia Geniostoma, Tabernæmontana, Fagræa, Bischoffia, Macaranga, and
Ficus. The widely-ranging species is in many genera polymorphous.
(4) _The absentees from Tahiti._ Amongst the orders are the Meliaceæ,
the Rhizophoreæ, and the Coniferæ. Amongst the genera, usually those
with “stones” or large seeds an inch in size, such as Canarium,
Dracontomelon, Myristica, Sterculia, Veitchia, &c. Numerous other
absent genera might be named.
FIJI.—_The Fijian genera not found either in Tahiti or Hawaii._ These
genera compose about half the Fijian flora, being at least 160 in
number. Those especially discussed here are the following:—Hibbertia,
Cananga, Sterculia, Trichospermum, Micromelum, Canarium,
Dracontomelon, Begonia, Geissois, Dolicholobium, Lindenia, Myrmecodia,
Hydnophytum, Couthovia, Limnanthemum, Myristica, Elatostema,
Ceratophyllum, Gnetum, Veitchia, Rhaphidophora, Lemna, Wolffia,
Scirpodendron. The Coniferæ are dealt with in Chapter XXIV.
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Note appended on Marsilea
HAVING completed our discussion of the general dispersal of tropical
genera, chiefly Indo-Malayan, over the Pacific islands, we pass on now
to consider the more restricted distribution of non-endemic genera over
this region. Here as before we take Hawaii, Tahiti, and Fiji as the
three centres of distribution; and here also we deal with the flowering
plants after excluding the orchids, the sedges, the grasses, the
mountain-plants, and all plants introduced either by the aborigines or
by white men.
HAWAII.
After excluding the endemic genera as well as those that are confined to
the mountains, we find that this group possesses very few genera that do
not occur in the Fijian and Tahitian regions, and fewer still that it
owns in common with Tahiti to the exclusion of Fiji. On the other hand,
we observe that Fiji possesses a great number of genera, mostly Asiatic
in origin, that have not reached Hawaii, and in several cases are not
known, from the Tahitian region. These contrasts might have been
expected, since the Pacific islands have in later ages been mainly
stocked from the Asiatic side of the Pacific, the principal route lying
through the Fijian region.