HYDROPTERIDEAE ╭ Marsiliaceae.
╰ Salviniaceae.
The unsatisfactory and meagre records in regard to the past history
of these heterosporous Filicales render superfluous more than a brief
reference to the recent species.
Marsiliaceae.
This family is usually spoken of as including the two genera _Marsilia_
and _Pilularia_. Lindman[1202] has however founded a third genus,
_Regnellidium_, on a Brazilian plant which is distinguished by some
well-defined characters from all species of _Marsilia_. The members
of the Marsiliaceae live for the most part in swampy situations.
_Marsilia_ is represented in Europe by _M. quadrifoliata_ L. which
occurs in Portugal, France, Germany and other parts of the Continent,
extending also to Kashmir, Northern China, and Japan. Of the other 53
species, 17 are recorded from different regions in Africa, while others
occur in South America, Asia[1203], Australia, and elsewhere.
_Pilularia globulifera_ L. is the only British representative of the
Hydropterideae. The remaining four species of the genus occur in South
America, California, New Zealand, Australia, and _P. minuta_ Dur. is
met with in the South of France, Algeria, and Asia Minor in subtropical
or warm temperate regions.
The Marsiliaceae are regarded as more nearly related to the
Schizaeaceae than to any other family of homosporous ferns[1204].
Their heterospory, the production of sporangia in closed fruit-like
sporocarps, and the anatomical features associated with existence in
marshy habitats, tend to obscure the resemblances to the true ferns.
• • • • •
The genus _Marsilidium_ proposed by Schenk[1205] for a piece of an
axis, bearing apparently a whorl of six leaflets, from the Wealden of
Osterwald, cannot be regarded as satisfactory evidence of the existence
of the Marsiliaceae in the Wealden flora of North Germany.
The six leaflets of _Marsilidium speciosum_, having a length of 5
cm., are similar in shape to the four leaflets of recent species of
_Marsilia_, but they differ in the repeated dichotomy of the veins from
the reticulate venation of the recent forms. It is worthy of note,
however, that in Lindman’s Brazilian type _Regnellidium diphyllum_
(fig. 326, A), the leaflets are characterised by dichotomous and not by
anastomosing veins.
Hollick[1206] has described some impressions of imperfect orbicular
leaves with a “finely flabellate obscurely reticulated(?) venation”
from Cretaceous rocks of Long Island as _Marsilia Andersoni_, but
these are too fragmentary to be accorded this generic designation. My
friend Dr Krasser informs me that he is describing some well-preserved
leaves from Cretaceous beds of Grünbach in Lower Austria as _Marsilia
Nathorsti_[1207]. He compares these with the recent form _Marsilia
elata_, a variety of _M. Drummondi_.
Another Lower Cretaceous species _Marsilia perucensis_ has been figured
by Frič and Bayer[1208] as a stalked fruit-like body from Bohemia. This
was originally described by Velenovský as _M. cretacea_, but under
this name Heer[1209] had previously recorded a supposed sporocarp from
Greenland. These fossils have little claim to recognition as examples
of Marsiliaceous plants.
The fragment figured by Heer[1210] from Tertiary rocks of Oeningen
as _Pilularia pedunculata_ is too small to determine with reasonable
accuracy. Other supposed representatives of the family mentioned in
palaeobotanical literature are not of sufficient importance to describe.
Salviniaceae.
The two genera of Salviniaceae, _Salvinia_ and _Azolla_, are water
plants, and are usually described as annuals which survive the less
favourable season in the form of detached sporocarps. Goebel[1211]
states that all the tropical species of _Salvinia_ known to him have an
unlimited existence.
_Salvinia natans_, Hoffm., the only European species, extends from the
South of France to Northern China and the plains of India: the other
twelve species are mostly tropical. _Azolla_, represented by four
species, occurs in Western and Southern North America, South America,
Madagascar, Australia, New Zealand, and is widely spread in tropical
Asia and Africa.
Species of _Azolla_ frequently form a considerable proportion of the
floating carpet of vegetation on inland waters[1212] growing under
conditions which might be supposed favourable for preservation in a
fossil state.
The Salviniaceae, though probably rather farther removed than the
Marsiliaceae from the homosporous Filicineae, are considered by
Bower[1213] to be related to the Gradatae, but modified in consequence
of their aquatic habit and the assumption of heterospory.
No undoubted examples of fossil species of _Azolla_ have been
described. _Salvinia_, on the other hand, is represented by several
Tertiary species, for the most part founded on leaves only, and
Hollick[1214], who published a list of fossil Salvinias, has described
detached leaves as _Salvinia elliptica_ Newb. from what may be Upper
Cretaceous rocks from Carbonado, Washington. Some of the leaves
figured as Tertiary Salvinias are of no value as evidence of the former
distribution of the genus[1215].
From the Coal-beds of Yen-Bäi (Tonkin), probably of Miocene age,
Zeiller[1216] has figured some well-preserved impressions of oval or
orbicular leaves, 15 mm. long and 10–20 mm. broad, characterised by
reticulate venation and by cordate bases, which he refers to Heer’s
Swiss species _Salvinia formosa_[1217].
Dr Zeiller[1218] in the most recently published part of his series of
valuable résumés of palaeobotanical literature refers to a description
by Brabenec of specimens of this species from Bohemian Tertiary beds
showing both microspores and megaspores.
One of the most complete specimens so far discovered has recently
been described by Fritel[1219] from Eocene beds of the Paris Basin
as _Salvinia Zeilleri_. This species, founded on portions of stems
bearing floating leaves, submerged root-like leaves, and sporocarps, is
compared with a recent tropical American species _S. auriculata_.
It is noteworthy that no authentic records of Hydropterideae have been
discovered in Palaeozoic rocks[1220]. Comparisons have been made in
the case of the genera _Traquairia_ Carr. and _Sporocarpon_ Will. with
the reproductive organs of _Azolla_[1221], but these rest on a wholly
insufficient basis.
Dawson[1222] proposed the generic name _Protosalvinia_ for some spores
of Devonian age, which he regarded on inadequate grounds as evidence of
Palaeozoic Hydropterideae.
Zeiller[1223], in discussing the possible relationships of the
problematical type _Chorionopteris gleichenioides_ Cord., suggests a
possible alliance with the Hydropterideae. Corda founded the genus
_Chorionopteris_[1224] on some small fragments of pinnules, 6–7 mm.
long, found in the Carboniferous rocks of Radnitz in Bohemia.
The lobes of the pinnules are incurved distally to form a capsule,
containing four sporangia, which apparently opened on dehiscence into
four valves; the spores are of one size. The material is however
insufficient for accurate determination.
There is no evidence contributed by fossil records which indicates
a high antiquity for the Hydropterideae. It is unsafe to base any
conclusion on the absence of undoubted Palaeozoic representatives of
this group; but the almost complete absence of records in pre-Tertiary
strata is a fact which may be allowed some weight in regard to the
possible evolution of the heterosporous filicales at a comparatively
late period in the earth’s history.
A description of the Mesozoic genus _Sagenopteris_ may be conveniently
included in this chapter, though as in many other instances the
inclusion of a genus under the heading of a recent family name does not
by any means imply that the position of the extinct type is regarded as
settled.
Sagenopteris.
This generic name was applied by Presl[1225] to small fronds composed
of four or rarely two palmately disposed leaflets with a more or less
distinct midrib and anastomosing secondary veins. Schimper[1226]
compared _Sagenopteris_ with _Marsilia_, but did not regard the
resemblance as evidence of relationship. Nathorst[1227] expressed
the opinion that certain fruit-like bodies obtained from the Rhaetic
beds of Scania are of the nature of sporocarps and were borne by
_Sagenopteris_, with the leaves of which they were associated. He
published a drawing of part of a fruit showing on its partially
flattened surface some raised oval bodies which are considered to
be spores. Dr Nathorst kindly placed at my disposal the drawings
reproduced in fig. 325 made from some of his specimens found at Bjuf in
Scania.
In contour and superficial features, e.g. the veining on the wall,
these bodies bear a fairly close resemblance to the sporocarps of
recent species of _Marsilia_. They were found in association with
the leaves of _Sagenopteris undulata_ Nath., an abundant Scania type
similar in form to the English Jurassic species _S. Phillipsi_ (figs.
327, 328). Heer was independently led by an examination of some
examples of the Swedish “fruits” to compare them with the sporocarps
of _Marsilia_. A small spherical body is figured by Zigno[1228] close
to a leaf of his species _S. angustifolia_, which may be a sporocarp.
In a recent paper, Salfeld[1229] says that he found fructification
on the lower face of the leaflets of _S. Nilssoniana_ Brongn. from
German Jurassic rocks, but he brings forward no evidence in support
of this statement. The systematic position of _Sagenopteris_ is by
no means settled. In a previous account of the genus I expressed the
view that it is probably a member of the true ferns[1230], but the
resemblance of Dr Nathorst’s drawings to the Marsilian sporocarps
influences me in favour of his opinion that _Sagenopteris_ may belong
to the Hydropterideae. The evidence, as Solms-Laubach[1231] states,
is not wholly satisfactory: Schenk points out that the frequent
occurrence of detached _Sagenopteris_ leaflets suggests that they
easily fell off the petiole, whereas in _Marsilia_ the leaflets do not
fall off independently. The discovery of a new type of Marsiliaceae in
Brazil, which Lindman has described as _Regnellidium diphyllum_[1232]
(fig. 326, A), affords an additional piece of evidence bearing on
the comparison of _Sagenopteris_ with members of this family. In
_Regnellidium_ the leaves differ from those of _Marsilia_ in bearing
two instead of four leaflets, and in the former the veins are
repeatedly forked, and do not anastomose as in _Marsilia_. In the
possession of only two leaflets _Regnellidium_ agrees with some forms
of _Sagenopteris_ (fig. 328).
[Illustration: FIG. 325. Sporocarp-like bodies found in association
with the leaves of _Sagenopteris_. (Nat. size. From drawings
supplied by Dr Nathorst.)]
[Illustration: FIG. 326.
A. _Regnellidium diphyllum_ Lind. Single leaf and stalked sporocarp.
(⅞ nat. size. After Lindman.)
B. Cuticle of _Sagenopteris rhoifolia_. (After Schenk.)]
_Sagenopteris Phillipsi_ (Brongniart)[1233]. Figs. 327, 328.
1828. _Glossopteris Phillipsi_, Brongniart, Hist. vég. foss. p. 225,
Pls. LXI. _bis_, LXIII.
1838. _Sagenopteris Phillipsi_, Presl, in Sternberg’s Flor. Vorwelt,
vii. p. 69.
[Illustration: FIG. 327. _Sagenopteris Phillipsi._
A. From the type-specimens of Lindley and Hutton (_Glossopteris
Phillipsi_). Gristhorpe Bay, Yorkshire. British Museum, No.
39221. Slightly reduced. M.S.
B. From a specimen in the British Museum (39222). Nat. size.
Figured by Lindley and Hutton as _Glossopteris Phillipsi_.]
The fronds of this common Jurassic species, which is recorded from
many European localities, from North America, Australia, the Antarctic
regions[1234], and elsewhere, are very variable as regards the form,
size, and number of the leaflets.
Frond petiolate, in some forms the petiole bears four linear or
oval-lanceolate leaflets having a distinct midrib and oblique
anastomosing veins. In others a shorter winged petiole bears one
or two shorter and broader, somewhat obcuneate, leaflets without a
midrib.
It is probable that Bunbury[1235] was correct in his opinion that the
specimen figured by Lindley and Hutton[1236] as _Otopteris cuneata_,
characterised by two leaflets (fig. 328), is not specifically distinct
from the normal form with four leaflets (fig. 327).
Similarly, such specimens as that represented in Pl. XVIII., fig.
3 of the first part of my _Jurassic Flora_, in which a short stalk
bears only one leaflet may, provisionally at least, be included in
Brongniart’s species. Yabe[1237] describes a form with two leaflets
from Jurassic rocks of Korea as _Sagenopteris bilobata_ which resembles
_S. Phillipsi_; and Moeller[1238] records a specimen similar to that
represented in fig. 328 from Bornholm as _S. cuneata_ (Lind. and Hutt.).
[Illustration: FIG. 328. _Sagenopteris Phillipsi._ From a specimen in
the Manchester University Museum. Nat. size.]
The leaf shown in fig. 327, A, in which the longest segments are 4·5
cm. in length, represents the most abundant form and illustrates the
very close agreement between _S. Phillipsi_ and the Rhaetic species
_S. rhoifolia_. Fig. 327, B, which is drawn from a specimen figured by
Lindley and Hutton[1239], shows a leaf with longer (6·5 cm.) and much
narrower segments. Broader leaflets are occasionally met with in which
the lamina reaches a length of 11 cm.[1240]
Leaves with leaflets narrower (3 mm. broad) than those represented in
fig. 327, B, are described by Zigno[1241] from Jurassic beds of Italy
as _S. angustifolia_ and by Moeller[1242] from the Jurassic of Bornholm
as _S. Phillipsi_ f. _pusilla_. A coarser type of venation than that of
_S. Phillipsi_ is occasionally found in Jurassic examples, as in _S.
grandifolia_ Font.[1243] from Oregon and _S. Nathorsti_ Barth. from
Bornholm[1244].
• • • • •
_Sagenopteris_ is recorded also from several Rhaetic floras. The best
known species, _S. rhoifolia_ Presl[1245], is hardly distinguishable
from some forms of _S. Phillipsi_ or from the Italian Jurassic species
described by Zigno as _S. Goeppertiana_[1246], though the leaflets are
usually rather larger. This species was first described by Brongniart
as _Filicites Nilssoniana_[1247], and a few authors[1248] have adopted
this specific name because of its priority over Presl’s designation.
As Nathorst remarks, to give up the well-known name _S. rhoifolia_ for
_S. Nilssoniana_ is “mere pedantry.” The epidermis of _S. rhoifolia_
as figured by Schenk[1249] consists of cells with straight and not
undulating walls: stomata occur on the lower surface (fig. 326, B).
Rhaetic leaves of the type represented by _S. rhoifolia_ have a wide
geographical distribution.
The specimens described by Feistmantel from the Damuda series of India
as _Sagenopteris longifolia_ are no doubt fronds of _Glossopteris
longifolia_[1250].
The Wealden species _Sagenopteris Mantelli_ (Dunk.)[1251] agrees
closely in habit and in the form of the leaflets with _S. Phillipsi_
and _S. rhoifolia_. It is probable that some of the leaves described by
Velenovský[1252] from Lower Cretaceous rocks in Bohemia as _Thinnfeldia
variabilis_ are portions of _Sagenopteris_ fronds. _S. Mantelli_ is
recorded from several European localities, from California[1253], and
elsewhere.
_Sagenopteris_ appears to have been widely distributed during
the Rhaetic, Jurassic and Lower Cretaceous floras. The very great
similarity between the specimens recorded from these three formations
renders the genus an uncertain guide in regard to geological age.
Decisive evidence as to its position in the plant kingdom is at present
lacking: the inclusion of the genus as a possible member of the
Hydropterideae has still to be justified.