THE FAMILIES OF FLOWERING PLANTS AND THEIR RELATIONSHIP
There are perhaps over 150,000 different kinds of flowering plants known
in the world to-day, but the flowerless ones are fewer than these in
numbers. No one really knows how many thousands of the cryptogams there
may be in the world, for all of them have not yet been described, and
there are doubtless thousands of which we merely suspect the existence.
Flowering plants are so much better known, and have for 2,000 years been
the subject of scientific writings, that their relationships and obvious
groupings into families are fairly definite and often easily
recognizable.
In our ordinary discussions or gossip of neighbors or relatives, the
absolutely necessary starting point is to know their name. Their
acquirement of this by christening, or by the adoption of it through the
usage of parents, settles for life what they will be called. Plants are
also christened, and that ceremony is one of the most important events
in our subsequent discussion of them.
PLANT NAMES AND HOW THEY ARE ACQUIRED
As we always have at least two names, one to show that we are a Smith,
for instance, and another to fix us as John Smith, so all plants have
two names, sometimes three.
And because plants come from all over the world and are studied and
loved by people of many different languages, it became necessary very
early in the descriptive writings about them to hit upon some device
that should insure the name of a particular plant being the same all
over the world, whether used by a student in the Imperial University of
China, or by a garden enthusiast in Connecticut. At the time when this
need for christening plants with names that would pass current
throughout the world was getting to be a crying necessity, the language
of all learned men was Latin, so it was natural that they should give
Latin names to plants. That practice has continued to the present day,
and there are even now some botanists that cling to the old custom of
describing the newly christened plant in Latin. In the olden days this
was always done, so that much of our knowledge of plants has come down
to us from early books written wholly in Latin. The unfamiliarity of
Latin to most of us, and the terrifyingly difficult spelling of some
plant names, has resulted in many people saying: “God made the flowers,
but the devil gave them names.” Nevertheless, these Latin names are the
only ones we can use without endless confusion, just as we bear the
names assigned to us by our parents, and no others.
If we were to go out into the country and pick up a wild rose which
seemed to be different from any other rose, it would be necessary, in
order to talk about it subsequently, to give it a name. After carefully
searching through all the books about roses and finding out that it
really is a new kind of rose rather than merely being new to us, we
should then be ready to christen our new find. As we have said, all
plants bear two names. One of these is a general one, like Smith, for
instance, and the other more specific, like John. These general names of
plants, and they are always their first names, are, because they fix the
plant as belonging to a particular group, known as generic names. The
generic name of violets, for instance, is _Viola_; of buttercups,
_Ranunculus_; of wheat, _Triticum_; of corn, _Zea_; and of roses,
_Rosa_. Our new rose then bears, without any act of ours, the generic
name _Rosa_, which was applied to roses many years ago, and must
therefore be used for all subsequently discovered roses. This generic
name of _Rosa_, like all other generic names, tells us that roses are a
well-recognized group of plants, all more like one another than like
blackberries, for instance, and because of this they are said to all
belong to the same genus. A genus (plural, genera) is a group of
different plants, all more like one another than like anything else. To
go back to our new _Rosa_, we must now apply its second and more
specific name. If it were a white rose, and had never before been
described, we should almost certainly use for its second name something
signifying its color and assign _alba_ as the obvious Latin equivalent
of white. The second name is always called the specific name, because it
shows us that from all other roses our new _Rosa alba_ differs in being
white. It is of the genus _Rosa_, but it is also and forever after a
recognized member of _Rosa_, to which a specific name has been
applied--in other words, _Rosa alba_ is a species of rose. Species are
thus plants more like one another than they are like any other member of
the genus to which they belong. _Rosa alba_ is a species quite unlike
_Rosa lucida_, or _Rosa carolina_, or all the other scores of roses
already known or described. At the time of christening _Rosa alba_, we
should not only enter its name in a book, as ours would be in a parish
register, but do much more than that. We should so carefully describe it
and, preferably, illustrate it with a picture that no one coming after
could ever mistake _Rosa alba_ for any other rose. It can be readily
seen that the christening of new plants is very nearly as serious an
affair as christening babies, and furthermore, it is only to be
attempted by experts. Because this has not always been done, many plants
have been christened two or three times. Of course, these subsequent
christenings do not seriously matter, for plants, like ourselves, should
have only one specific name, the first applied to them. But their
subsequent christenings by the careless and ignorant have enormously
increased the difficulty of talking or writing about plants. These
spurious names are common throughout the literature of botany and are
known as synonyms.
The thing to remember about plants, so far as our need for classifying
them is concerned, is that they belong to different species which might
almost be considered the unit or simplest recognizable category into
which they may be sorted. For convenience, we sort species into genera
which may well be considered the next highest category in which plants
are grouped. The grouping of genera into tribes, of tribes into
families, and of families into still larger categories, has nothing to
do with their names, but everything to do with our understanding of how
they are related to one another, and what these different categories
mean in the great collection of plants all about us. In other words, it
reduces to a definite system an apparently hopelessly mixed-up mass of
plants that, without some contrivance of the sort, would simply be a lot
of totally unrelated specimens of plant life. Actually they are grouped
in fairly definite categories, some of which are easily recognizable,
and all of which fit into that great scheme of nature where everything
may seem chaotic, but to the observant it is really a very pattern of
order. What it all means and how plants have been grouped into families
will be explained, now that we understand how they have acquired their
generic and specific names.
PLANT FAMILIES AND ORDERS
A scientist once visiting in Bulgaria noticed that the peasants in that
country frequently lived over a hundred years and, in trying to find out
the reason, he discovered that they drank large quantities of sour milk.
This is alive with a definite kind of bacterium that is of great benefit
to the digestive apparatus, and therefore helps in the prolongation of
life. In Bulgaria, in other words, a certain food habit of the people
has resulted in a definite prolongation of life and fixes that
population as of somewhat different characteristics from people not
addicted to sour milk. In Japan a whole race lives largely on fish and
rice, and while this is not the cause of their yellow skin, it is almost
surely the cause of their generally small stature. Many of the English
are tall, light-haired, and blue-eyed people, fond of outdoor life and
sports, and among the most highly developed of the peoples of the earth.
The climate of that island, their generally large consumption of meat
and the outdoor life of so many of them, have resulted in quite definite
characteristics that make the typical Englishman an easily
distinguishable type.
In studying man we are able not only to divide him into such broad
divisions as white, black, and yellow races, but due to their particular
country or mode of life there are scores of racial subdivisions of these
larger categories that everyone recognizes. Such differences are often
based on stature, shape of head, mental characters and many others, but
those still finer shades of difference between, for instance, a
Connecticut Yankee and a plantation owner in the South, are, while noted
by everyone, very difficult to accurately describe.
In attempting to find such major differences in plants, some structural
character that would set off one large group of plants from every other
group, the botanist has a harder task than the person studying man. For
all those differences of language and mentality that make up such a
large part of our common knowledge of the different peoples of the earth
are characters that are foreign to plants. We are thus thrown back on
structure as the chief way in which plants differ, and because their
reproductive organs are their most important ones, and therefore least
likely to vary, it is upon certain characters of these organs that all
flowering plants have been divided.
In the chapter on “How Plants Produce Their Young,” we found that most
flowering plants have their ovules in an ovary which, after
fertilization, develop into fruit and seed. But some plants, while they
have ovules, only bear them naked or between scales, never inclosed in
an ovary. This is true in all pines, spruces, hemlocks, and all the host
of their generally evergreen relatives. Such trees bear cones, between
the scales of which are perfectly naked ovules that develop into seeds
(Figure 77) that have never been hidden in an ovary, as have the vast
majority of the seeds of other plants (Figure 53). These naked-seeded
plants are known as _gymnosperms_ or literally _gymnos_, naked, and
_sperma_, seed, and comprise all the cone-bearing trees in the world,
the larger part of which are always evergreen. In some past ages such
trees made up the bulk of vegetation of the earth, but at present they
are much reduced in numbers. Familiar examples of these _Coniferæ_, or
cone-bearing trees, are larch, spruce, fir, pine, hemlock, juniper, and
yew.
[Illustration: FIG. 77.--THE JERSEY PINE
(_Pinus virginiana_)
A gymnosperm or naked-seeded plant. Note the seeds dropping from between
the scales of the cone.]
Most of these are evergreen, which does not, of course, mean that they
bear the same leaves always, but that only a few drop off at a time and
are so constantly renewed that the tree is actually ever green.
All other flowering plants always bear their ovules in an ovary and,
because of this fact, are called _angiosperms_, literally _angeion_, a
vessel, and _sperma_, seed. These inclosed seeded plants comprise the
great bulk of the vegetation of the earth to-day. So far as the
temperate zone is concerned, nearly all of them drop their leaves in the
fall, and the trees belonging to the angiosperms are thus said to be
deciduous trees.
No better idea of the present size and importance of these two groups of
plants can be gained than to state the fact that perhaps not over 500
different kinds of gymnosperms, all of which are trees and shrubs, are
known. All the rest of the flowering plants in the world, comprising
over 150,000 different kinds of herbs, shrubs, and trees of infinite
variety, are angiosperms and therefore bear ovules in an ovary, followed
by seeds in or on some sort of a fruit. It would almost seem as though
the simplest way to dispose of this great mass of plants would be to
sort them into trees, shrubs, and herbs. For all of them belong to one
of these types of plant growth, and the ancient students of plants, just
before the time of Christ, actually divided all flowering plants into
these three classes. This, of course, threw the coniferous trees in with
all other kinds and, as we have already seen, they differ from all other
kinds in the important character of having naked ovules.
Here, again, in order to get some system out of apparent chaos, we must
fall back on some fundamental character. And, again, it is the product
of the reproductive process in all this host of angiosperms which
furnishes the clue. In the seeds of many of them the young embryo has
folded up within it two seed leaves, while in all the rest only one. As
we saw in Chapter I, these seeds germinate either with a single seed
leaf, like corn (Figure 85), or with two seed leaves, like beans (Figure
81). Every one of these angiosperms belongs to one of these classes or
the other, and perhaps more extraordinary still is the fact that in
those with one seed leaf there are associated certain leaf and flower
characters, while those with two seed leaves are always very different.
In the monocotyledons, or plants with a single seed leaf, the leaves are
practically always parallel veined (Figure 83), like corn and grass, and
lilies and palms, and hundreds of others. Also, they nearly always have
the parts of their flowers in threes (Figure 84). That is, they have
three sepals, petals, stamens, and often pistils, or multiples of three.
The common trillium or wake-robin, for instance, has three sepals, three
petals, six stamens, and three styles. With a few exceptions, and nature
seems to delight in producing a few such, all monocotyledons have this
parallel-veined leaf character and flower parts in threes or multiples
of three.
Plants which send up two seed leaves (Figure 81), on the other hand,
bear practically always netted-veined leaves (Figure 79), and the parts
of their flowers are nearly always in fours or fives or multiples of
these numbers (Figure 80). The well-known wild geranium has five sepals,
five petals, ten stamens, and a five-lobed or five-celled ovary. There
is some individual variation from this plan, sometimes one organ and
sometimes another having more or less than the regular number. But so
overwhelmingly true are these distinctions that dicotyledons, or plants
with two seed leaves, and monocotyledons,
[Illustration: FIGS. 78-85.--PLANT FAMILIES
Dicotyledonous and Monocotyledonous growth habits contrasted. Figs.
78-81. The trunk of a dicotyledonous tree showing division of the wood
into heartwood, sapwood, and cambium, which the removal of a piece of
outer bark exposes. Note the net-veined leaf (79), the seedling with two
seed leaves (81), and with the parts of the flower in 5’s (80). Figs.
82-85. Monocotyledonous plant. Note the lack of zones of wood, cambium
and corky bark. Such plants have parallel-veined leaves (83), parts of
their flowers in 3’s or 6’s (84), and germinate with a single seed leaf
(85).]
or plants with a single seed leaf, have been for hundreds of years the
two great classes into which all angiospermous flowering plants are
divided.
Our general view of all the flowering plants may be summarized then as
follows:
1. Gymnosperms, or naked seeded plants, include all cone-bearing plants,
mostly evergreen and always trees or shrubs. The pine is a familiar
example.
2. Angiosperms, or inclosed seeded plants, include all other flowering
plants of whatever kind. Divided into: (_a_) Monocotyledons. Sprouting
with one seed leaf, and leaves practically always parallel-veined. Parts
of the flower in threes or multiples of three. Familiar examples are
corn, grass, sugar-cane, palms, cannas, and lily of the valley (Figures
82-85). (_b_) Dicotyledons. Sprouting with two seed leaves, and the
leaves practically always netted-veined. Parts of the flower in fours or
fives or multiples of these numbers. Includes all the remaining
flowering plants and is a larger group than the monocotyledons and the
cone-bearing plants combined (Figures 78-81).
No matter from what part of the world a totally unfamiliar plant may
come, it is always possible to decide into which one of these groups it
belongs. That in itself tells us a good deal about its ancestors and its
future, “places” it, in fact, in one of those major groups into which
all plants are divided. No other characters that plants possess are so
important in determining their true position in the scale of plant life
as those we have briefly outlined. But merely to sort plants into these
large groups does not tell us all we need to know about them. For all
plants not only belong to monocotyledons, or dicotyledons, or
gymnosperms, but also to smaller divisions of these groups. Just as
white men are divided into Englishmen, Frenchmen, etc., so there is the
greatest necessity of dividing our large plant groups into smaller and
more precise categories.
Some of the chief subdivisions of these large groups have been decided
upon the fact that a considerable number of plants in them have some
character in common, not found in the remaining plants of the group.
Among the monocotyledons, for instance, there is a large class of plants
that have tiny flowers between dry, chaffy scales, bear no true petals
or sepals, all wind pollinated and are all commonly, though incorrectly,
called grasses. These include, strictly speaking, two groups; one, the
true grasses in which the stem is mostly hollow and the fruit a grain,
while the other, with solid stems and bearing achenes for fruits, are
the sedges. The grasses form one family and the sedges another, but
while they differ in the characters just mentioned they agree in having
flowers of the same general type. Families of plants are thus groups of
genera, placed together in the scheme of classification, because they
are more like one another than like any other such group. Among the
grasses, for instance, are corn, wheat, rice, bamboo, orchard grass,
Kentucky blue grass, sugar cane, and hundreds of others, all belonging
to different genera, but all those genera grouped into a single family
because of their generally similar flowers. Just as the Kentucky blue
grass has a generic name (_Poa_) and a specific one (_pratensis_), the
families of plants must also bear names, usually derived from the
generic name of one of the chief genera in it. Because _Poa_ is a large
and important genus of the grasses, the family is named after it, with
the addition of _ceæ_. _Poaceæ_ is thus the family name of all the
grasses. Among the sedges one of the commonest genera is _Cyperus_,
including many species of the galingale or earth almond. From this genus
the sedge family has been named _Cyperaceæ_ (Figure 87). So the rose
family is the _Rosaceæ_, the violet family is _Violaceæ_, and so on
through all the three hundred or more families which contain all the
flowering plants so far discovered. Going back for a moment to the
_Poaceæ_ and _Cyperaceæ_, the fact that these two large families are
different from each other, but have some characters in common, fixes
them as both belonging to one _order_. Orders are thus groups of one or
more plant families, all differing one from another, but obviously
related and having some characters in common. The order containing the
grasses and sedges is named for one of the families in it with the
ending _ales_. Thus _Poales_ include _Poaceæ_ and _Cyperaceæ_. _Rosales_
include _Rosaceæ_ and several families.
In other words, individual plants are grouped in species, species into
genera, genera into families, and families into orders. These orders are
themselves grouped into still larger divisions; there are, for instance,
twelve orders comprising all the monocotyledons, and about twenty orders
comprising all the dicotyledons. Once we have decided that any plant is
a monocotyledon or a dicotyledon, our next step should be as to which
order it belongs, then its family, its genus, and finally its species.
Needless to say, such studies are necessarily of a technical nature, and
while the details of them lie outside the scope of this book, the
general plan or scheme of flowering plant classification is as we have
outlined it above.
This scheme of plant classification has been developed not only for our
convenience in sorting plants into definite categories, but more
important still to show, if possible, the relationships, and
particularly the development from the simplest to the most complex types
of plant life. Thus the monocotyledons begin with the cat-tails, which
have mere bristles for calyx and corolla, and lead by infinite
gradations to the showy and highly complex orchids, which are considered
the climax of the monocotyledonous families. While no general account of
the plant families can be attempted here, some of the more interesting
in both the monocotyledonous and dicotyledonous groups will be briefly
discussed.
SOME MONOCOTYLEDONOUS PLANT FAMILIES
Of the simple plants of this group the Grass Family, or _Poaceæ_ (Figure
86), is the most important, for in it are all our turf grasses, the
bamboo and sugar cane, besides scores of others. Over 4,500 species are
known, and they inhabit every region of the globe. The steppes of Russia
and our Great Plains are predominately grassy; in the wonderful bamboo
forests in the tropics are also woody representatives of this family.
Certain kinds in the tropics grow as vines, with great hooked spines at
the joints, so that nearly every kind of growth-form is to be found in
the _Poaceæ_. All agree in having very small flowers, arranged in tiny
spikelets, which are themselves grouped in various ways, although the
inflorescence is usually some form of spike, or raceme or panicle. The
individual flowers are between chaffy scales, of which several make up
each spike. Always the lowest two scales are empty, and the flowers
begin in the third from the bottom, or
[Illustration: FIG. 86.--BLUE-JOINT GRASS
(_Calamagrostis canadensis_)
FIG. 87.--WOOL GRASS
(_Scirpus Cyperinus_)
Fig. 86. Blue-joint grass, a common grass of North America and a member
of the _Poaceæ_. Fig. 87. Wool-grass, a tall swamp sedge popularly but
incorrectly spoken of as grass. It is a member of the _Cyperaceæ_ or
Sedge family, which have usually triangular solid stems, whereas grasses
have hollow round stems.]
sometimes even above that. The flower is so simple that there is neither
calyx nor corolla, only three stamens and one to three styles. The fruit
is a grain and the Poaceæ, therefore, are the chief source of cereals.
Wheat, rice, corn, oats, barley, millet, and rye, all come from grasses,
and all, except corn, are natives of the Old World. They were grown for
countless ages before the discovery of America, when Europeans first saw
corn used by the Indians. As they are wind-pollinated, the flowers of
grasses produce no honey nor colored petals, and the vast majority of
them have no odor. Most of them reproduce, not only by seeds, but by
rootstocks, and many of them grow so closely together that they form
turf. In nearly all of them the stem is hollow, and in the largest of
them, the bamboo, these hollow stems are used as water and sewer pipes,
especially in India. An exception to the hollow stem is the sugar cane,
from whose solid stem the juice is pressed out, that is the chief source
of sugar; and our common Indian corn.
[Illustration: FIG. 88.--SHOWY WAKE-ROBIN
(_Trillium grandiflorum_)
A plant of the lily family (_Liliaceæ_). Note the tendency to net-veined
leaves in a monocotyledonous plant. Such instances are common in nature
and net-veined leaves are found in certain species of smilax and most of
the plants of the Arum family, containing the jack-in-the-pulpit, both
monocotyledons.]
Much more highly developed than the grasses is the lily family or
_Liliaceæ_ (Figure 88), but comprising less than 1,500 species in about
125 genera. They are nearly always herbs, but the Spanish bayonet forms
a woody trunk, while the dragon tree of the Canary Islands is an
extraordinary plant for a lily relative, one giant specimen of this
being 80 feet tall and over 45 feet in circumference.[1] The flowers in
the _Liliaceæ_ are nearly always perfect, that is, stamens and pistils
are found in the same flower. Its perianth segments are nearly always
six, sometimes distinguishable as petals and sepals, but more often, as
in the tulip, all colored similarly. The fruits are practically always a
capsule that splits lengthwise. Perhaps the different plants in the
_Liliaceæ_, as well as any others, illustrate the fact that plants of
any particular family need not look like one another in order to be
included in the same family. Nothing could be farther from resemblance
than the bulb-bearing onion, the tulip, the Easter lily, the Spanish
bayonet, and the dragon tree. Yet they and hundreds of other plants
belong to the _Liliaceæ_. It cannot be overemphasized that it is flower
and fruit characters that determine inclusion in any plant family, and
similarity of leaves or habit may or may not accompany such characters.
Among other well-known plants in the family, which is found throughout
the world, are the crocus, the day lily, the dogtooth violet, hyacinth,
and colchicum and aloes used in medicine. Many of them produce bulbs,
such as onion, tulip, and lily and some of these contain valuable foods
and drugs. The great majority of them are insect fertilized and are
therefore wonderfully colored, and some furnish rich stores of honey.
But the most highly developed and interesting of all the
monocotyledonous plants are the orchids (Figures 89-92). This family,
_Orchidaceæ_,
[Illustration: FIG. 89.--ROSE POGONIA
(_Pogonia ophioglossoides_)
FIG. 90.--YELLOW-FRINGED ORCHID
(_Blephariglottis ciliaris_)
Fig. 89. Rose pogonia. A native bog orchid with purplish-pink flowers.
Fig. 90. Yellow-fringed orchid. A bog and meadow orchid of the eastern
United States.]
comprises over 6,000 species and many varieties, the overwhelming
proportion of which live in the tropics. Perhaps 90 per cent of them are
epiphytes, or air plants, which are perched high up on the branches or
bark of trees, and take all their food and water from the air. All the
native orchids of temperate North America grow in the ground, however,
and their food habits are unique. They depend for food upon a
microscopic organism found inside the roots of all orchids, and which
helps them to take in the food from the soil. So many of these orchids
are partial saprophytes, and without the associated organism they could
not grow. Almost uniformly the
[Illustration: FIG. 91.--WHORLED POGONIA
(_Isotria verticillata_)
FIG. 92.--ARETHUSA
(_Arethusa bulbosa_)
Fig. 91. Whorled pogonia. A woodland orchid with the leaves and flowers
whorled at the apex of the stem. Fig. 92. Arethusa. The most beautiful
of our bog orchids, with a fringed lip and pinkish-purple flowers which
bloom about Decoration Day. Note the highly irregular flowers in this
and Figs. 89-91.]
_Orchidaceæ_ have only a very few sheathing leaves, entirely without
marginal teeth, and some kinds are practically leafless. The flowers,
among the most gorgeous in the world, are always irregular in the sense
that there is no obvious series of sepals and petals. Both these are so
much transformed as to be nearly unrecognizable as such, but in some
orchids there appear to be three sepals. More often of the three inner
segments of the flower two are somewhat alike, while the third is quite
unlike them and is known as the lip; it is among the most variable of
any parts of the orchid flower. As adapted to insect visitors, the
flowers of orchids are the most wonderfully developed of all plants.
Because of their beauty and strange shapes, orchids have been much
sought after by collectors, and explorations of tropical, fever-ridden
forests have not infrequently ended in death to orchid hunters. New and
rare species of them are constantly being gathered by these collectors.
One expedition to New Guinea found over 1,000 kinds never before known,
and in the last few decades over 4,000 new orchids have been discovered.
For these plants orchid fanciers pay large sums, and a single plant of a
rare one sold in London at auction for over $500. The chances of
collecting such species made expeditions to the tropics frequent during
the latter half of the last century.
These three families, Poaceæ, Liliaceæ, and Orchidaceæ, are perhaps the
most important of all the monocotyledons, although commercially the
palms, or Palmaceæ, are extensively used. It is impossible to describe
or even mention all the monocotyledonous families, but a list of the
more important is added. The families are arranged in the order that
seems to reflect the development from simpler ones to the most complex,
and is the sequence of such families used by nearly all botanists in
describing the plant families of the world:
_Typhaceæ_--The cat-tails. Tall, reedlike swamp plants found throughout
the world. One genus and about ten species.
_Pandanaceæ_--The screw pines. Shrubs or trees with stout, woody trunks
and mostly prickly margined, long sword-shaped leaves. Confined to the
Old World tropics.
_Poaceæ_--The grasses. Noted above.
_Cyperaceæ_--The sedges. Grasslike plants with solid, often triangular
stems. Very often inhabitants of wet places. Throughout the world, Crex
rugs are made from a species of Carex, the largest genus in the family.
About 75 genera and 3,200 species.
_Palmaceæ_--The palms. All trees or shrubs, or sometimes climbing vines.
Includes the coconut and palm-oil trees, two palms of tremendous
economic importance. Inhabitants of tropical and warm regions, and only
very few found in the United States. Over 130 genera and 1,200 species.
_Araceæ_--The arums, of which the jack-in-the-pulpit is our best-known
native representative. They are nearly always herbs, often of giant
size, and the great majority are found in the tropical regions. Flowers
very minute, crowded together on a central column (the spadix), and this
often surrounded or having at its base a leaflike appendage (the
spathe). Calamus root and the skunk cabbage are also native
representatives. About 105 genera and over 900 species.
_Liliaceæ_--The lily and related plants, noted above.
_Smilaceæ_--Smilax. Mostly prickly vines; our native kinds often called
cat briers. Sarsaparilla comes from at least four species of _Smilax_.
Three genera and about 300 species, mostly natives of tropical, but a
few of temperate regions.
_Amaryllidaceæ_--The amaryllis family, noted chiefly for the sisal fiber
that comes from a species of _Agave_, which is one of the many different
kinds of century plant. The family has usually capsular fruits and black
seeds, and the narcissus and amaryllis of our gardens are well-known
members. About 70 genera and 800 species from tropical and warm
countries; a few in temperate regions, mostly herbs.
_Iridaceæ_--The iris, the source of orris root, and containing some our
most beautiful garden plants, the blue-eyed grass of fields, and over 50
genera and 100 species are found in this family. Nearly throughout the
world, and nearly all herbs.
_Musaceæ_--The banana and traveler’s-tree. Giant herbs, in the banana
having the largest leaves known, frequently twelve feet long and two
wide. Natives of tropical and warm regions, and 4 genera and 75 species
are known. Flowers often very irregular, and in _Strelitzia_ gorgeous.
_Orchidaceæ_--The orchids, already noted.
While there are many thousands of plants contained in these
monocotyledonous families and in the others not mentioned here, they
make up only about one-third of the total number of different kinds of
plants known in the world. But in grasses and sedges, in the rushes and
a few other families, the number of individuals is greater than in
probably any other plant family.
DICOTYLEDONOUS PLANT FAMILIES
All the great bulk of the flowering plants not included in the
monocotyledons or the gymnosperms belong to about two hundred plant
families that are included in the dicotyledons. In all of them the seed
sends up two seed leaves, there are generally netted-veined leaves and
the parts of the flower are in fours or fives or multiples of these
numbers. In such a large aggregation of plant families there are three
well-marked divisions, namely, those that bear no petals or sepals,
those that do bear them and where they are separated to form individual
sepals or petals, and those where the petals are united to form some
sort of a tubular or at least connected corolla. These divisions are
perhaps best shown thus:
(_a_) _Apetalæ_--Including families where the petals are never present,
and in some there is even no calyx. Examples: walnut, hickory, willow,
and oaks.
(_b_) _Polypetalæ_--Petals present but separate, not forming a tubular
or connected corolla. Examples: buttercup, rose, pea, apple, geranium.
(_c_) _Gamopetalæ_--Petals united and forming some sort of a tubular or
connected corolla. Examples: garden primrose, gentian, salvia, mint,
snapdragon, and the daisy family.
Any attempt to describe the families contained in these three divisions
of the dicotyledons would take all the rest of this book and crowd out
other things about plant life that must not be omitted. All that can be
done here is to outline briefly a few families in each division so that
we shall have fixed in our minds what the general principles of plant
classification are and how these are illustrated by well-known plants.
There are many books that deal with this subject in great detail and to
them the student should go for further elaboration of the subject. It is
one of the most interesting phases of the study of botany, but it
demands a longer and more intensive study than can be included here.
(_a_) _Apetalæ_--These include families of plants that are the simplest
in structure of all the dicotyledons. In all of them there are no petals
and in some both petals and sepals are lacking, leaving only essential
organs. Taking first those families that have neither petals nor sepals
we find that most of them bear their flowers in catkins, a flower
cluster familiar enough in the pussy willow. Some of these families are
the following:
_Juglandaceæ_--Trees with compound leaves, flowers in catkins and fruits
inclosed in a thick husk. Examples: walnut and hickory. Six genera and
over 30 species.
_Salicaceæ_--Shrubs or trees with simple leaves, flowers in catkins and
capsular many-seeded fruits, but no nuts. Containing only willows and
poplars. Two genera and over 200 species. (Figure 93.)
_Myricaceæ_--Shrubs or trees with simple usually fragrant leaves,
flowers in catkins and fruits one-seeded. The bayberries. Two genera and
about 35 species. (Figure 94.)
[Illustration: FIG. 93.--PRAIRIE WILLOW
(_Salix humilis_)
The _Salicaceæ_, consisting only of willows and poplars, are always
woody plants bearing their flowers in catkins.]
These and some other families of close relationship are the least
developed, in their flower structure, of any of the dicotyledons. All of
them bear only the essential organs of reproduction in their very simple
flowers. In the walnuts and hickories the different sexes are in
different flowers on the same plant, in the willows they are even on
different plants, and in Myricaceæ they are often found both ways. All
of these flowers are wind-pollinated, so that they bear no honey,
usually have no odor, and of course their need for showy petals for
attracting insects is nil, although some pollen-eating insects visit
them.
[Illustration: FIG. 94.--SWEET FERN
(_Comptonia peregrina_) belonging to the _Myricaceæ_.
These are usually aromatic, always woody plants, of which several
species besides sweet fern grow in the United States.]
Somewhat higher in the scale of plant life are those families that,
while still lacking petals, do have sepals. Their flowers are for this
reason much better protected against rain or other inclement conditions,
which means that they are so much the more likely to reproduce their
kind. At least two of these slightly more developed families cling to
the habit of bearing some of their flowers in catkins, however. Other
families are also found in other parts of the world, but in North
America this group is represented by:
[Illustration: TRANSPLANTING RICE IN JAVA
(_Courtesy of Brooklyn Botanic Garden._)]
[Illustration: A TEA ESTATE IN CEYLON
(_Courtesy of Brooklyn Botanic Garden._)]
_Betulaceæ_--The birch, alder, hazelnut, and hornbeam. Both staminate
and pistillate flowers in catkins. Fruit a small one-seeded nut or a
winged samara in the birch. All wind-pollinated. Six genera and about
seventy-five species, nearly all from north temperate zone.
[Illustration: FIG. 95.--LOW BIRCH
(_Betula pumila_)
A bog shrub of the _Betulaceæ_ or birch family. Most of them are tall
trees with both male and female flowers in catkins.]
_Fagaceæ_--The oaks, beech, and chestnut. All trees or shrubs with at
least their staminate flowers in catkins. Fruit inclosed in a bur
(chestnut and beech) or borne in a cup (the acorns of oaks). At least
five genera and about 375 species, widely distributed.
The habit of bearing some or all their flowers in catkins which flower
usually before the leaves appear, and of having such flowers wholly at
the mercy of precarious winds, is, if not lost, at least much less
frequent in the remaining families of the apetalæ. All the others, while
still without petals, do have sepals and some of these are colored so
that insect visitors are likely. There are too many of these families to
be enumerated here, but two of the chief are:
_Ulmaceæ_--The elms and hackberry. Trees or shrubs with minute greenish
or yellowish flowers crowded in small clusters or in spikes. Fruit a dry
nut or one-seeded and winged; or in the hackberry a drupe, one of the
first evidences of even a slightly fleshy fruit in the dicotyledons.
About 13 genera and 140 species, widely distributed.
_Polygonaceæ_--The buckwheat, knotweeds, common dock, and many other
genera. Sepals often colored white or pink so the flowers are sometimes
at least insect-pollinated. Flowers small and crowded in various
clusters, often in a spike. Fruit an achene, a dry fruit familiar enough
in the buckwheat. About 40 genera and over 800 species, mostly herbs or
vines here, but often trees in the tropics.
From here on plant families leave, with some exceptions, the greenish or
otherwise inconspicuous flower color, and somewhere about here they
begin to rely more upon insect fertilization for the perpetuation of
their kind. None of those so far mentioned have any petals to their
flowers, but in the pink family or Caryophyllaceæ we find the first
evidences on any considerable scale of the presence of sepals and
petals, the latter usually beautifully colored. Familiar representatives
of this family are the pink, carnation, chickweed, corn cockle, and the
stichwort. There are over 50 genera and 1,000 species, nearly all in
temperate regions.
The apetalous families appear to show a development from catkin-bearing
trees with the sexes separated, and with neither petals nor sepals,
through the Polygonaceæ, with often colored sepals, and the beginnings
of insect fertilization. In Caryophyllaceæ, the most highly developed of
them all, there are, besides the sepals, often or usually petals, and
the reliance on insect fertilization is nearly complete. There are many
transitional stages which cannot be included here, but they show step by
step the development of the apetalous families from perfectly naked
reproductive organs to the next larger group, the polypetalæ, where the
process of increasingly complex flower development will now be sketched.
(_b_) _Polypetalæ_--In this large group of plant families the petals are
free and quite separate, but as if they had not yet lost all the
characters of the apetalæ, some families show incompletely the general
characteristics of their more stable neighbors. There are, for instance,
no petals in many species of the buttercup family, none in the sweet-gum
tree nor in the maples, and a few others. But in spite of occasional
exceptions this large group of polypetalous families do usually bear
separate petals and sepals, and are among the most important of all the
plant families. As they number over a hundred and contain thousands of
species, all that can be done here is to mention a few typical or
important ones. Just as in the apetalæ the families in this large group
appear to show definite stages in development from simpler to more
complex forms. But the steps are harder to trace and what appears
simple characters in some plants are very complex in others.
While all the families in this group have separate petals some of them
show a tendency to have united sepals, a character of perhaps some
advantage and certainly very common among the still more developed
gamopetalæ. Some of the families that have separate sepals agree in
having the stamens inserted below the ovary. Of these the following
three families may serve as types.
_Nymphæaceæ_--The water lilies. Aquatic plants with usually large showy
flowers in which the calyx, corolla, and stamens often merge one into
the other so that it is sometimes difficult to know where one series
ends and the other begins. Five genera and 45 species throughout the
world.
_Ranunculaceæ_--Buttercup family. Includes buttercups, clematis,
columbine, meadow rue, golden seal, marsh-marigold, hepatica, and scores
of other native plants. All herbs, except a few semiwoody vines like
clematis. Sepals always present, and where no petals are found, as in
marsh-marigold, colored like them. Highly irregular flowers are not
uncommon, as in columbine and monkshood. The fruits are berrylike in
some genera and in others dry capsules. Thirty-five genera and over
1,000 species throughout the world, but most abundant in temperate
regions.
_Lauraceæ_--Laurel or sassafras family. Includes besides them the guava
and cinnamon and camphor trees, all tropical, and the native spice-bush.
All trees and shrubs with small, yellow, or greenish-yellow flowers and
usually aromatic juice. Fruit a one-seeded drupe or a berry. About 40
genera and over 1,000 species, nearly all tropical, but a few in the
United States.
At this point, in the sequence of plant families, there are two or three
families that bear quite different fruits than any heretofore noted, and
in one of them, at any rate, the four petals are in the form of a cross.
So uniformly is this true that the family was for years known as the
Cruciferæ, but is better known as Brassicaceæ, from _Brassica_, the
generic name of the mustard. This large mustard family mostly has fruits
known as a silique or silicle, which are pods that split into two
valves; and yellow or white, rarely pinkish flowers. The juice is always
somewhat acrid, familiar through the pleasant pungent taste of
water-cress, but none of the family is poisonous. There are over 200
genera and nearly 2,000 species of wide distribution, and common
representatives include the cress, mustard, horse-radish, garden stock,
sweet alyssum, cabbage, cauliflower, brussels sprouts, radish, and
turnip.
Between the Brassicaceæ and the following families there are many others
that cannot be mentioned here. Somewhat farther along in the sequence
are a group of families, large and important, and all having their
stamens inserted around or even above the ovary, and in which the sepals
are partly or wholly united. They include some of our most beautiful
flowers and useful fruits. Of the many closely related families that
agree in these characters the two most important are:
_Rosaceæ_--Rose family. In the broad sense including, besides the rose,
the strawberry, blackberry, apple, pear, peach, plum, besides many herbs
with wholly dry fruits. There are always five petals, five lobes to the
partly united calyx, but numerous stamens. They may be herbs, shrubs,
or trees, with simple or compound leaves, but these are nearly always
alternately arranged. There are over 100 genera and nearly 2,000
species. Because of the size of the Rosaceæ and differences in fruit,
the apple and its relatives are often included in a separate family, the
Malaceæ (Figure 96), and the peaches and plums in Amygdalaceæ. The
general structure of the flower is sufficiently uniform, however, for
them all to have been included in Rosaceæ (Figure 97).
[Illustration: FIG. 96.--WASHINGTON THORN
A prickly shrub related to the apple, which, with the plums, cherries,
pears, strawberry, blackberry and hundreds of other plants are all
grouped in the _Rosaceæ_ or rose family.]
_Papilionaceæ_--Pea family. A large family having characteristic pealike
flowers, a description of which has already been given in Chapter I.
They all bear legumes, a pod that splits down one side, not both, as in
Brassicaceæ. Besides the pea, the bean, vetch, alfalfa, lentil, locust
tree, and dozens of valuable timber trees in the tropics belong here.
Flowers all showy and absolutely dependent upon insects for
fertilization. Seeds highly nutritious in many genera, and the roots of
nearly all have bacteria associated with them. (See chapter on Food
Habits of Plants.) Three hundred and twenty-five genera and over 5,000
species of wide distribution, but most frequent in the tropics.
[Illustration: FIG. 97.--THIMBLEBERRY
(_Rubus odoratus_)
A bristly shrub of the Rose family common in rocky places in eastern
North America.]
There are many other smaller families in different parts of the world
which hover, as it were, about these two giant plant families that make
definite landmarks in the scheme of plant classification. The character
of having partly united sepals and numerous stamens inserted around, or
even above the ovary, give to all the flowers of the Rosaceæ and related
plants a general family resemblance that is very striking. The pea
family, and its relatives, also have flower and fruit characters of
remarkable uniformity, considering the tremendous number of species.
From this point on to the end of the polypetalæ there are scores of
plant families, all agreeing in having a compound ovary, that is, one
that is more than one-celled, and in also having quite distinct and
separate sepals. Their agreement in these characters, however, ends all
other evidences of relationship, and it is beyond the scope of this book
to go into the details of each, or even a few of them. A list with some
brief notes on those most important must suffice here.
_Geraniaceæ_--Geranium family. Includes also the common garden as well
as the wild geranium. Fruit splitting into five parts. Leaves always
divided or even dissected; 12 genera and 470 species, all herbs.
_Anacardiaceæ_--Includes the tree of heaven, sumac, poison ivy, and in
the tropics, the mahogany, all trees, shrubs, or vines; 60 genera and
500 species, mostly in the tropics.
_Malvaceæ_--Mallow family, including, besides the marshmallow, the rose
of Sharon, and cotton. They all have the stamens united into a column or
tube which surrounds the style. About 40 genera and 900 species of
herbs, shrubs, or trees of wide distribution.
_Cactaceæ_--Cactus family. Nearly all desert plants, with no leaves or
practically none, and greenish stems that function as leaves and also
store water. Of the greatest variety of form and always bearing numerous
petals and fleshy fruits, of which the prickly pear is familiar enough.
Of 40 genera and over 1,000 species, all, but a handful, come from North
and South America.
_Umbelliferæ_ (often called _Ammiaceæ_)--The climax of the polypetalous
families, and nearly always bearing flowers in umbels. There are usually
many flowers, sometimes several hundred in each cluster. Familiar
examples are parsley, celery, parsnip, Queen Anne’s lace, and many
others. The seeds often contain an aromatic oil, as in caraway, and some
are violently poisonous, as the water hemlock. About 250 genera and over
2,000 species, all herbs, widely distributed, but most common in
temperate regions.
We have seen from the foregoing the probable development of
dicotyledonous plants from those simplest ones, where, as in the pines,
there is merely a naked ovule between scales, through the catkin-bearing
trees, without petals or sepals, and all wind-pollinated, to families
where just an inconspicuous and, subsequently, a colored calyx is found,
and after this the dawn of those plants that have complete and perfect
flowers. Among the latter all those so far noted have separate petals,
but after the Ammiaceæ, or carrot family, there appears a new character,
setting off practically all other dicotyledonous plants from those
already treated. This new character--and hints of it are found before it
reaches the perfection found in the subsequently described families--is
that of the petals being united to form some sort of a connected or,
more often, a tubular corolla. The petals are represented merely by the
lobes of the corolla, mostly four or five, and in many families of this
group, known as the gamopetalæ, literally, united petals, this tubular
corolla is irregular and often beautifully formed. In salvia, for
instance, there is a hoodlike upper part overhanging the lower tubular
part. Other familiar examples of these irregular corollas are the garden
snapdragon, Oswego tea, skullcap, pentstemon, and many others.
(_c_) _Gamopetalæ_--The earlier families among those generally having
united petals seem not yet quite sure of their new character, for a few
of them hark back to the condition of having, in some genera, quite
separate petals. One of the first families in this series, the Ericaceæ
(Figure 98), or heath family, has several genera in which this is true,
notably in the Labrador tea and the sand myrtle among native plants, and
some foreign relatives. The Ericaceæ are almost exclusively shrubs or
trees, but some of our native sorts, such as trailing arbutus and
wintergreen, are practically herblike, although they are, strictly
speaking, woody plants. The family is remarkable for containing
beautiful flowered garden plants, such as the hundreds of species of
South African heaths, the heather, the azaleas and rhododendrons, and
our beautiful native Rhodora, about which Emerson wrote one of his most
beautiful poems. The flowers in the heath family are often perfectly
regular and bell-shaped, but sometimes irregular, as in azaleas and
several other genera. Nearly all the family rely on microscopic
organisms to get their food, and some close relatives, like the Indian
pipe, are saprophytes. There are over 70 genera and 1,200 species widely
distributed. Central Asia is the home of most rhododendrons and azaleas,
scores of species being found in the upper reaches of the Himalayas.
The Ericaceæ are typical of many families in the first group of the
gamopetalæ, in that all of them, with a few exceptions like the
cranberry, have a superior ovary. That is, the petals and sepals arise
from the base or below the ovary, and consequently the mature fruit in
such plants is never crowned with the remains of the withered calyx, as
blueberries always are and all other gamopetalæ that have an inferior
ovary. The character of having an inferior or superior ovary separates
the gamopetalæ into two large groups of families, the heath family and
many others, with superior ovary, and a few but numerically very
important families that always have an inferior ovary.
[Illustration: FIG 98.--SWAMP AZALEA
A shrub of the _Ericaceæ_, with white or pink sticky flowers and dry
capsular fruits.]
Taking first the families that all have a superior ovary, we must, for
lack of space, exclude most of them from here. A few of the most
important, or typical, after the Ericaceæ, are:
_Primulaceæ_--Primrose family. All herbs in which the stamens are as
many as the lobes of the corolla and inserted on them. The flowers are
quite regular. They all have some form of a capsule for fruit, which in
most generally split lengthwise. Familiar examples include the garden
primrose (not the wild evening primrose), yellow loosestrife, the star
flower, pimpernel, shooting star, and the beautiful cyclamens. A few
members of the family are slightly luminous in the dark, apparently an
attraction to night-flying insects. About 28 genera and over 400
species, mostly from the northern hemisphere, a few in temperate South
America and South Africa.
_Gentianaceæ_--Gentian family. Over 700 species in 70 genera, all bitter
herbs, with opposite leaves, quite without teeth and beautiful,
sometimes fringed, always regular flowers. In this and related families
the stamens are of the same number as the lobes of the corolla, and
always alternate with them. Gentian and sea or marsh pinks are our
best-known native representatives, while some related plants are
medicinal.
There are many other families in this part of the scheme of plant
classification that have minor differences among themselves, but agree
pretty generally in the number and position of their stamens, their
superior ovary, and, on the whole, in the regular flower. Irregular and
regular flowers may be recognized at once by cutting them lengthwise
through the middle. In regular flowers there would be as much on one
side as on the other of the dividing line, and in irregular ones quite
obviously more on one side than the other. The character of all the
genera in a family having irregular flowers begins to occur here with
greater and sometimes exclusive frequency. In the mint family, or
Lamiaceæ, nearly all of its 160 genera and over 3,000 species have
two-lipped or irregular flowers. The garden salvia well illustrates the
type.
The _Lamiaceæ_ or Labiatæ, as they are often called from the two-lipped
corolla, are herbs locally, but in the tropics often shrubs or trees.
Almost universally they have four-sided stems and opposite leaves
without stipules. The flowers may be solitary, much more often they are
crowded into various kinds of clusters. The four stamens are borne on
the corolla tube, and nearly always there are two long and two short
ones. The family is universally fertilized by insects, and some of the
flowers are wonderfully adapted for this end. Common examples, besides
the salvia, are mint, thyme, skullcap, hyssop, bugle, blue curls,
catnip, hedge-nettle, coleus, and Oswego tea. Most of the genera contain
heavy odorous oils in their foliage, from which oil of mint, pennyroyal,
lavender, rosemary, marjoram, savory and balm are the best known. These
volatile oils give to members of the family their characteristic and
often very beautiful odors.
There are many other families of plants, some with irregular and others
with regular flowers, that appear to group themselves around the
Lamiaceæ, all of which agree, in spite of individual differences, in
having a superior ovary. The remaining families of the gamopetalæ,
however, always have an inferior ovary, usually obvious by the insertion
of petals above the ovary, and in the fruit often conspicuous by the
remains of the withered calyx still clinging to the top of the fruit.
Only two of the scores of families, with inferior ovary and gamopetalous
corollas, will be mentioned here, both of which are important.
_Rubiaceæ_--Madder family. Common examples are the creeping bedstraw,
the sweet woodruff, partridge berry, button bush, and bluets or
quaker-ladies. All, except one of these, are herbs, but in the tropics
the Rubiaceæ are nearly all shrubs or trees. Among those are the coffee,
quinine, and ipecac. All the family have opposite leaves (a few
verticillate) and stipules, regular flowers, with stamens as many as
the corolla lobes, and alternate with them. The fruits are a drupe,
berry, or capsule. Over 340 genera and 6,000 species are known almost
throughout the earth.
_Compositæ_ or _Carduaceæ_--The daisy family and the largest and most
complex of all the plant families. As the culmination of the scheme of
plant classification, they show the greatest perfection in the
arrangements for cross-fertilization. For a description of their flower
structure, see Chapter I, page 44, and Figures 43-45. Some of the
Compositæ have no ray flowers, others are all ray flowers, but the great
bulk of them bear both tubular and ray flowers in a single head. This
may be single, or more commonly it is arranged in various kinds of
clusters. Each head is surrounded at its base by one or more series of
usually tightly overlapping bracts, incorrectly called a calyx by the
unobservant. The Compositæ include over 900 genera and 11,000 species
from all parts of the world. Most of them in America are herbs. Daisy,
dandelion, dahlia, chrysanthemum, sunflower, boneset, chicory, lettuce,
and scores of other examples could be cited, all herbs. In the tropics
the Compositæ are more often trees and shrubs. The family contains many
economic plants such as arnica, chamomile, artichokes, inula, and many
others.
This all too brief account of the grouping of plants in families, and
the sequence of these from the comparatively simple naked-seeded pines,
through monocotyledons, the apetalous dicotyledons, followed by the
polypetalous dicotyledons, and culminating in the Compositæ among the
gamopetalous families, gives us merely a hint of what are the characters
upon which plants are divided. While the details are necessarily
omitted, the gradual development from naked-seeded plants, wholly at the
mercy of the elements, up to those which are marvelously provided with
contrivances to insure cross-fertilization, has been traced. Perhaps no
other phase of botanical study offers such a rich opportunity as this,
for upon the solution of some of the problems of plant classification
depends the answer to many questions about the history of the earth and
man’s ability to live on it. Certain of these plant families have lived
on the earth hundreds of thousands of years before man first came.
Others have apparently arisen comparatively recently. Many botanists
believe that all the monocotyledons should be placed after the
dicotyledons, as the latter may be a more ancient type than the former.
How these different plant structures, some very ancient and others more
recent, help to show us some of the history of the earth, will be
treated, among many other evidences of a plant nature, in the chapter on
“The History of the Plant Kingdom.”