FOSSIL FERNS.
=Osmundaceae.=
From the Culm of Silesia, Stur[761] described impressions of sterile
fronds which he named _Todea Lipoldi_ on the ground of the similarity
of the finely divided pinnules to those of _Todea superba_ and
other filmy species of the genus. The type-specimen of Stur (in
the Geological Survey Museum, Vienna) affords no information as to
sporangial characters and cannot be accepted as an authentic record
of a Lower Carboniferous representative of the family. Another more
satisfactory but hardly convincing piece of evidence bearing on the
presence of Osmundaceae in pre-Permian floras has been adduced by
Renault[762], who described petrified sporangia from the Culm beds of
Esnost in France as _Todeopsis primaeva_ (fig. 256, F). These pyriform
sporangia are characterised by the presence of a plate of large cells
comparable with the subapical group of “annulus” cells in the sporangia
of the recent species (fig. 221).
Zeiller[763] has published a figure of some sporangia described by
Renault from Autun resembling the Osmundaceous type in having a plate
of thick-walled cells instead of a true annulus, but the plate is
larger than the group of cells in the recent sporangia, and both
sporangia and spores are smaller in the fossil. The sporangia from
Carboniferous rocks described by Weiss as _Sturiella_[764] bear some
resemblance to those of recent Osmundaceae, but there is no adequate
reason for referring them to this family.
The generic name _Pteridotheca_ is employed by Scott as a convenient
designation for unassigned petrified sporangia of Palaeozoic age with
an annulus and other characters indicating fern-affinity. In the
species _P. Butterworthi_[765] the sporangia are characterised by a
group of large cells suggesting comparison with the annulus, or what
represents the annulus, in Osmundaceae and Marattiaceae. Scott has also
described a sporangium from the Coal-Measures containing germinating
spores[766]; the structure is similar to that of recent Osmundaceous
sporangia, and it is interesting to note that germinating spores have
been observed in the recent species _Todea hymenophylloides_[767].
Additional evidence of the same kind is afforded by fertile specimens
of a quadripinnate fern with deeply dissected oval-lanceolate pinnules
described by Zeiller from the Coal-Measures of Heraclea in Asia Minor
as _Kidstonia heracleensis_[768] (fig. 256, E). Carbonised sporangia
were found at the base of narrow lobes of the ultimate segments and,
as seen in fig. 256, E, the sporangial wall is distinguished by a
plate of larger cells occupying a position like that of the “annulus”
of recent Osmundaceae. Zeiller regards the sporangia as intermediate
between those of Osmundaceae and Schizaeaceae. From the same locality
Zeiller describes another frond bearing somewhat similar sporangia as
_Sphenopteris_ (_Discopteris_) _Rallii_ (fig. 256, D)[769]: the term
_Discopteris_ was instituted by Stur for fertile fronds referred by him
to the Marattiaceae[770].
It is by no means safe to assume that these and such Upper
Carboniferous sporangia as Bower[771] compared with those of
_Todea_ were borne on plants possessing the anatomical characters
of Osmundaceae rather than those of the extinct Palaeozoic family
Botryopterideae. This brings us to the important fact, first pointed
out by Renault, that the Botryopterideae are essentially generalised
ferns exhibiting many points of contact with the Osmundaceae[772].
It is clear that whether or not we are justified in tracing the
Osmundaceae as far back as the Lower Carboniferous period, some of the
characteristics of the family were already foreshadowed in rocks of
this age.
Through a fortunate accident of preservation, unequivocal evidence of
the existence of Osmundaceae in the Palaeozoic era is supplied by the
Russian Upper Permian genera _Zalesskya_ and _Thamnopteris_.
_Zalesskya._
This generic title has been instituted by Kidston and
Gwynne-Vaughan[773] for two Russian stems of Upper Permian age, one
of which was named by Eichwald[774] _Chelepteris gracilis_, but the
probability that the type of the genus _Chelepteris_ is generically
distinct from Eichwald’s species necessitated a new designation for the
Permian fern.
In habit the stem of _Zalesskya_ resembles that of an _Osmunda_ or a
_Todea_, but it differs in the possession of a stele composed of a
continuous cylinder or solid column of xylem surrounded by phloem,
and by the differentiation of the xylem into two concentric zones.
The leaves are represented by petiole-bases only; the sporangia are
unknown. The stem and leaf-base anatomy fully justifies the inclusion
of _Zalesskya_ in the Osmundaceae.
_Zalesskya gracilis_ (Eichwald). Fig. 248.
The type-specimen is a partially decorticated stem, from Upper Permian
beds in Russia, provided with a single stele, 13 mm. in diameter,
surrounded by a broad thin-walled inner cortex containing numerous
leaf-traces and occasional roots: this was doubtless succeeded by a
sclerotic outer cortex. In its main features _Zalesskya gracilis_
agrees closely with _Z. diploxylon_ represented in fig. 249. The stele
consists of a continuous cylinder of xylem exhibiting a fairly distinct
differentiation into two zones, (i) a broader outer zone of narrower
scalariform tracheae (_x ii_, fig. 248) in which 20 to 25 protoxylem
strands (_px_) occur just within the edge, (ii) an inner zone of
broader and shorter tracheae (fig. 248, _x i_). The protoxylem elements
(_px_, fig. 248) are characterised by a single series of scalariform
pits, while the metaxylem elements have multiseriate pits like those
on the water-conducting elements of recent Osmundaceae. The tracheae
show an interesting histological character in the absence of the middle
substance of their walls, a feature recognised by Gwynne-Vaughan[775]
in many recent ferns. External to the xylem and separated from it
by a parenchymatous sheath is a ring of phloem, _ph_, composed of
large sieve-tubes and parenchyma separated from the inner cortex by a
pericycle 4 to 5 layers in breadth. The occurrence of a few sclerotic
cells beyond the broad inner cortex points to the former existence of
a thick-walled outer cortex. The leaf-traces are given off as mesarch
strands from the edge of the xylem; they begin as prominences opposite
the protoxylem and become gradually detached as xylem bundles, at first
oblong in transverse section, then assuming a slightly crescentic and
reniform shape, while the mesarch protoxylem strand takes up an endarch
position. As a trace passes further out the curvature increases and
the protoxylem strands undergo repeated bifurcation; it assumes in fact
the form and general type of structure met with in the leaf-traces of
_Todea_ and _Osmunda_. Numerous diarch roots, given off from the stele
at points just below the outgoing leaf-traces, pass outwards in a
sinuous horizontal course through the cortex of the stem.
[Illustration: FIG. 248. _Zalesskya gracilis_ (Eich.). Transverse
section of part of the stele: _ph_, phloem; _x i_, _x ii_, xylem;
_px_, protoxylem. (After Kidston and Gwynne-Vaughan. × 20.)]
[Illustration: FIG. 249. _Zalesskya diploxylon_. Kidston and
Gwynne-Vaughan. Transverse section of stem. _ph_, phloem. (After
Kidston and Gwynne-Vaughan. × 2½.)]
In _Zalesskya gracilis_ the xylem cylinder was probably wider
in the living plant than in the petrified stem. In _Zalesskya
diploxylon_[776], in all probability from the same Russian locality,
there can be little doubt that the xylem was originally solid to the
centre (fig. 249). In this species also the phloem forms a continuous
band (_ph_, fig. 249) consisting of four to six layers of sieve-tubes.
_Thamnopteris_.
_Thamnopteris Schlechtendalii_ (Eich.). Figs. 250, 312, A, Frontispiece.
In 1849 Brongniart[777] proposed the name _Thamnopteris_ for a species
of fern from the Upper Permian of Russia originally described by
Eichwald as _Anomopteris Schlechtendalii_. A new name was employed by
Brongniart on the ground that the fossil was not generically identical
with the species previously named by him _Anomopteris Mougeotii_[778].
Eichwald’s specimen has been thoroughly investigated by Kidston and
Gwynne-Vaughan[779]. The stem (Frontispiece) agrees in habit with
those of _Zalesskya_ and recent Osmundaceae; on the exposed leaf-bases
the action of the weather has etched out the horse-shoe form of the
vascular strands and laid bare numerous branched roots boring their way
through the petiole stumps. The centre of the stem is occupied by a
protostele 13 mm. in diameter consisting of solid xylem separated by a
parenchymatous sheath from a cylinder of phloem. The xylem is composed
mainly of an axial column of short and broad reticulately pitted
tracheae (fig. 250, _b_ and Frontispiece), distinguished from the
sharply contrasted peripheral zone of normal scalariform elements, _a_,
by their thinner walls and more irregular shape. The protoxylem, _px_,
is represented by groups of narrower elements rather deeply immersed in
the peripheral part of the metaxylem. A many-layered pericycle, _per_,
and traces of an endodermis, _en_, succeed the phloem, _ph_, which is
characterised by several rows of large contiguous sieve-tubes; beyond
the endodermis is a broad thin-walled inner cortex. The leaf-traces
arise as in _Zalesskya_, but the protoxylem in _Thamnopteris_ is at
first central; as the trace passes outwards a group of parenchyma
appears immediately internal to the protoxylem elements and gradually
assumes the form of a bay of thin-walled tissue on the inner concave
face of the curved xylem. The next stage is the repeated division of
the protoxylem strand until, in the sclerotic outer cortex, the traces
acquire the Osmundaceous structure (fig. 312, A, p. 453). The petiole
bases have stipular wings as in _Todea_ and _Osmunda_.
[Illustration: FIG. 250. _Thamnopteris Schlechtendalii_ (Eich.). Part
of stele: _a_, outer xylem; _b_, inner xylem. (After Kidston and
Gwynne-Vaughan. × 13.)]
[Sidenote: OSMUNDACEAE]
The striking feature exhibited by these Permian plants is the structure
of the protostele, which in _Thamnopteris_ and probably in _Zalesskya
diploxylon_ consists of solid xylem surrounded by phloem: this may be
regarded as the primitive form of the Osmundaceous stele. In _Osmunda
regalis_ and in other recent species of the genus the xylem cylinder
has the form of a lattice-work; in other words, the departure of
each leaf-trace makes a gap in the xylem and the overlapping of the
foliar-gaps results in the separation of the xylem into a number
of distinct bundles. In _Zalesskya gracilis_ the continuity of the
xylem is not broken by overlapping gaps; in this it agrees with
_Lepidodendron_. In _Thamnopteris_ the centre of the stele was occupied
by a peculiar form of xylem obviously ill-adapted for conduction, but
probably serving for water-storage and comparable with the short and
broad tracheae in _Megaloxylon_[780]. There is clearly a well-marked
difference in stelar anatomy between these two Permian genera and
_Todea_ and _Osmunda_: this difference appears less when viewed in
the light of the facts revealed by a study of the Jurassic species
_Osmundites Dunlopi_.
[Illustration: FIG. 251. _Lonchopteris virginiensis._ (After Fontaine.
½ nat. size.)]
As possible examples of Triassic Osmundaceae reference may be made
to some species included in Stur’s genus _Speirocarpus_[781]. _S.
virginiensis_ was originally described by Fontaine[782] from the Upper
Triassic rocks of Virginia as _Lonchopteris virginiensis_ (fig. 251)
and has recently been figured by Leuthardt[783] from the Keuper of
Basel. The sporangia, which are scattered over the lower surface of
the pinnules, are described as globose-elliptical and as having a
rudimentary apical annulus; no figures have been published. In habit
the frond agrees with _Todites Williamsoni_, but the lateral veins form
an anastomosing system like that in the Palaeozoic genus _Lonchopteris_
(fig. 290, B). There would seem to be an _a priori_ probability of
this species being a representative of the Osmundaceae and not, as
Stur believed, of the Marattiaceae. Seeing that _Lonchopteris_ is
a designation of a purely provisional kind, it would be convenient
to institute a new generic name for Triassic species having the
Lonchopteris venation, which there are good reasons for regarding as
Osmundaceous ferns.
Similarly _Speirocarpus tenuifolius_ (Emmons) (= _Acrostichites
tenuifolius_ Font.), which resembles _Todites Williamsoni_ (see p. 339)
not only in habit and in the distribution of the sporangia but also in
the venation, is probably an Osmundaceous species.
_Osmundites._
_Osmundites Dunlopi_, Kidston and Gwynne-Vaughan[784], fig. 252.
This species was found in Jurassic rocks in the Otago district of New
Zealand in association with _Cladophlebis denticulata_[785] (fig. 257).
The type-specimen forms part of a stem 17 mm. in diameter surrounded
by a broad mass of crowded leaf-bases. The stele consists of an almost
continuous xylem ring (fig. 252) enclosing a wide pith: the phloem and
inner cortex are not preserved but the peripheral region of the stem is
occupied by a sclerotic outer cortex. The mass of encasing leaf-bases
resolves itself on closer inspection into zones of foliage-leaf
petioles and the petioles of scale-leaves with an aborted lamina.
A similar association of two forms of leaf is seen in the existing
American species _Osmunda Claytoniana_ and _O. cinnamomea_. The cortex
and armour of leaf-bases are penetrated by numerous diarch roots.
The xylem cylinder, six to seven tracheae broad, is characterised
by the narrower diameter of its innermost elements and—an important
point—by the fact that the detachment of a leaf-trace does not break
the continuity of the xylem cylinder (fig. 252). Each leaf-trace is
at first elliptical in section; it then becomes curved inwards and
gradually assumes the horse-shoe form as in _Zalesskya_ and in the
recent species. The single endarch protoxylem becomes subdivided until
in the petiole it is represented by 20 or more strands.
[Illustration: FIG. 252. _Osmundites Dunlopi_ Kidst. and G.-V. Portion
of xylem showing the departure of a leaf-trace. (After Kidston and
Gwynne-Vaughan; × 36.)]
In the continuity of the xylem cylinder this species of _Osmundites_
shows a closer approach to _Todea barbara_ or _T. superba_ (fig. 221,
B) than to species of _Osmunda_; it differs from _Zalesskya_ in having
reached a further stage in the reduction of a solid protostele to one
composed of a xylem cylinder enclosing a pith. This difference is of
the same kind as that which distinguishes the stele of _Lepidodendron
rhodumnense_ from _L. Harcourtii_. In _Lepidodendron_ short tracheae
occasionally occur on the inner edge of the xylem cylinder, and in
recent species of _Todea_ the same kind of reduced tracheae are met
with on the inner edge of the xylem[786]. In both cases the short
tracheae are probably vestiges of an axial strand of conducting
elements which in the course of evolution have been converted into
parenchymatous cells. In _Lepidodendron vasculare_ the mixed parenchyma
and short tracheae in the centre of the stele represent an intermediate
stage in xylem reduction, and the arrangement in vertical rows of the
medullary parenchyma in _Lepidodendron_ is precisely similar to that
described by Kidston and Gwynne-Vaughan in _Thamnopteris_. In both
cases the rows of superposed short cells have probably been produced
by the transverse septation of cells which began by elongating as if to
form conducting tubes and ended by assuming the form of vertical series
of parenchymatous elements.
[Illustration: FIG. 253. _Osmundites Kolbei_ Sew. (⅓ nat. size.)]
In another Jurassic species, _Osmundites Gibbiana_[787], the xylem is
of the _Osmunda_ type and consists of about 20 strands instead of a
continuous or almost continuous cylinder.
[Illustration: FIG. 254. _Osmundites Kolbei._ (Leaf-scars.)]
_Osmundites Kolbei_ Seward, figs. 253–255.
This species was founded on a specimen obtained by Mr Kolbe from
the Uitenhage series of Cape Colony[788]. The fossil flora and fauna
of this series point to its correlation with the Wealden or Neocomian
strata of Europe[789]. The type-specimen consists of several pieces
of a stem (fig. 253) which reached a length of about 90 cm. On the
weathered surface the remains of petiole-bases are clearly seen and
on the reverse side of the smaller piece shown in the figure numerous
sinuous roots are present in association with the leaf-stalks. The
depression _c_ in the larger specimen may mark the position of a
branch: at _a_ fig. 253 (enlarged in fig. 254, _a_) the vascular strand
of a petiole is exposed as a broad =U=-shaped band and at _b_ (fig.
254, _b_) the form of the petiole-bases is clearly shown[790]. With the
stem were found imperfectly preserved impressions of fronds referred to
_Cladophlebis denticulata_, a common type of leaf which was found also
in association with the slightly older New Zealand stem, _Osmundites
Dunlopi_.
[Illustration: FIG. 255. _Osmundites Kolbei_ Sew. Transverse section,
from a photograph supplied by Dr Kidston and Mr Gwynne-Vaughan.
(2½ nat. size.)]
An examination of the internal structure of the South African stem
by Dr Kidston and Mr Gwynne-Vaughan has revealed many interesting
features, which will be fully described in Part IV. of their Monograph
on fossil Osmundaceous stems. I am greatly indebted to these authors
for allowing me to publish the following note contributed by Dr
Kidston:—
“The section of _Osmundites Kolbei_ Seward, shown in fig. 255, presents
the usual appearance of an Osmundaceous stock. The parts contained in
this section are the stele, inner and outer cortex and a portion of
the surrounding mantle of concrescent leaf-bases. The whole specimen
has suffered much from pressure, but if restored to its original form
the xylem ring must have been about 19 mm. in diameter. The number of
xylem strands is about fifty-six and several of them are more or less
joined as in the modern genus _Todea_. The tracheae are of the typical
Osmundaceous type, that is to say, the pits are actual perforations and
several series of them occur on each wall of the larger tracheae.
“The most interesting structural characteristic of _Osmundites Kolbei_
is not well seen in the figure owing to the compression of the xylem
ring. This consists in the occurrence of tracheae in the pith. In fact,
we have here a mixed pith, composed of parenchyma and true tracheae,
a condition which connects the _Osmundaceae_ with a parenchymatous
medulla with those possessing a solid xylem stele like _Zalesskya_ and
_Thamnopteris_ and so completes the series of transitions extending
from the older and solid-steled forms to the modern medullated members
of the _Osmundaceae_.”
_Osmundites skidegatensis_, Penhallow.
This lower Cretaceous Canadian species, first described by
Penhallow[791] and more recently by Kidston and Gwynne-Vaughan[792],
is remarkable for the large size of the stem, the stele alone having
a diameter of 2·4 cm. Penhallow figures a fragment of a leaf bearing
a superficial resemblance to that of _Osmunda Claytoniana_, which
may be the foliage borne by _Osmundites skidegatensis_. The xylem
cylinder is broken by the exit of leaf-traces into 50 or more strands
varying in size and shape, and it is noteworthy that the phloem is also
interrupted as each leaf-trace is given off. In recent species the
xylem cylinder is almost always interrupted, but the phloem retains its
continuity. In the Canadian fossil an internal band of phloem occurs
between the xylem and the pith, and this joins the external phloem at
each leaf-gap. This internal phloem finds an interesting parallel in
certain recent species[793], but in these the internal and external
phloem do not meet at the foliar gaps as they do in the extinct type.
In _Osmunda cinnamomea_ the internal phloem occurs only at the regions
of branching of the stem stele; in the fossil it is always present.
It is clear that _Osmundites skidegatensis_ represents the most complex
type of stem so far recognised in the Osmundaceae; it illustrates a
stage in elaboration of the primitive protostele in advance of that
reached by any existing species.
• • • • •
The primitive Osmundaceous stele was composed of solid xylem surrounded
by phloem (_Thamnopteris_ and _Zalesskya_); at a later stage the xylem
cylinder lost its inner zone of wide and short tracheae and assumed
the form seen in _Osmundites Kolbei_, in which the centre of the stele
consists of parenchyma with some tracheae. Another type is represented
by _O. Dowkeri_ in which the pith is composed wholly of parenchyma
and the xylem ring is continuous. From this type, by expansion of the
xylem ring and by the formation of overlapping leaf-gaps, the form
represented by _Osmunda regalis_ was reached. _Osmunda cinnamomea_,
with internal phloem in the regions of stelar branching, probably
represents a further stage, as Kidston and Gwynne-Vaughan believe, in
increasing complexity due to the introduction of phloem from without
through gaps produced by the branching of the stele. In _Osmundites
skidegatensis_ the leaf-gaps became wider and the external phloem
projected deeper into the stele until a continuous internal phloem
zone was produced. This most elaborate type proved less successful than
the simpler forms which still survive.
_Osmundites Sturii._
Impressions of fertile pinnae with narrow linear segments bearing
exannulate sporangia described by Raciborski from Lower Jurassic rocks
in Poland as _Osmunda Sturii_[794] may with some hesitation be included
in the list of Mesozoic Osmundaceae.
_Osmundites Dowkeri._
Under this name Carruthers[795] described a petrified stem from
Lower Eocene beds at Herne Bay, which in the structure of the stele
agrees closely with the Jurassic species _O. Gibbiana_ and conforms
to the normal Osmundaceous type. It is possible, as Gardner and
Ettingshausen[796] suggested, that the foliage of this species may be
represented by some sterile _Osmunda_-like fragments recorded from
the Middle Bagshot beds of Bovey Tracey and Bournemouth as _Osmunda
lignitum_.
_Todites._
This generic name[797] has been applied to fossil ferns exhibiting in
the structure of the sporangia and in the general habit of the fertile
fronds a close resemblance to the recent species _Todea barbara_ (fig.
221, D, p. 286).
_Todites Williamsoni_ (Brongniart) figs. 256, B, C, G.
1828. _Pecopteris Williamsonis_, Brongniart, Prodrome, p. 57; Hist.
vég. foss., p. 324, Pl. CX. figs. 1 and 2.
—— _P. whitbiensis_, Brongniart, Hist. vég. foss. p. 321, Pl. CIX.
figs. 2–4.
—— _P. tenuis_, _ibid._ p. 322, Pl. CX. figs. 3, 4.
1829. _Pecopteris recentior_, Phillips, Geol. Yorks. p. 148, Pl.
VIII. fig. 15.
—— _P. curtata_, _ibid_. Pl. VIII. fig. 12.
1833. _Neuropteris recentior_, Lindley and Hutton, Foss. Flora, Vol.
I. Pl. LXVIII.
—— _Pecopteris dentata_, _ibid._ Vol. III., Pl. CLXIX.
1836. _Acrostichites Williamsonis_, Goeppert, foss. Farn. p. 285.
1841. _Neuropteris Goeppertiana_, Muenster, in Goeppert, Gattungen
foss. Pflanz. Lief. 5 and 6, p. 104, Pls. VIII.–X.
1856. _Pecopteris Huttoniana_, Zigno, Flor. foss. Oolit. Vol. I. p.
133.
1867. _Acrostichites Goeppertianus_, Schenk, Foss. Flor. Grenzsch. p.
44, Pl. V. fig. 5, Pl. VII. fig. 2.
1883. _A. linnaeaefolius_, Fontaine, Older Mesoz. Flora Virginia, p.
25, Pls. VI.–IX.
— _A. rhombifolius_, _ibid_. Pls. VIII. XI.–XIV.
1885. _Todea Williamsonis_, Schenk, Palaeont. Vol. XXXI. p. 168, Pl.
III. fig. 3.
1889. _Cladophlebis virginiensis_, Fontaine, Potomac Flora, p. 70,
Pl. III. figs. 3–8; Pl. IV. figs. 1, 4.
[Illustration: FIG. 256.
A. _Cladophlebis denticulata._
B, B′. _Todites Williamsoni_ (fertile).
C. _T. Williamsoni_ (sterile pinna).
D. _Discopteris Rallii._
E, E′. _Kidstonia heracleensis._
F. _Todeopsis primaeva._
G. _Todites Williamsoni_ (sporangium).
[B, C, from specimens (13491; 39234) in the British Museum (B,
very slightly reduced; C, ½ nat. size); D, E, after Zeiller; F,
after Renault; G, after Raciborski.]]
It is hopeless to attempt to arrive at satisfactory conclusions in
regard to the applicability of the name _Todites Williamsoni_ to the
numerous fronds from Jurassic and Rhaetic rocks, agreeing more or less
closely with Brongniart’s type-specimen. Specimens from the Rhaetic may
not be specifically identical with those from the Jurassic; the main
point is that, whether actually identical or not, both sets of fossils
clearly represent the same general type of Osmundaceous fern[798] and
may for present purposes be included under the same designation. The
above synonymy, though by no means complete[799], serves to illustrate
the confusion which has existed in regard to this widely spread type of
Mesozoic fern.
_Todites Williamsoni_ may be briefly described as follows:—
Frond bipinnate; long linear pinnae (20–30 cm.) of uniform breadth
arise at an acute angle, or in the lower part of a frond, almost at
right angles, from a stout rachis. Closely set pinnules attached
by a broad base; slightly falcate, the side towards the rachis
strongly convex and the outer margin straight or concave and
bulged outwards towards the base of each segment, margin usually
entire, or it may be slightly lobed. Fertile pinnules similar to
the sterile; sporangia of the Osmundaceous type and often scattered
over the whole lower surface of the lamina (fig. 256, B, B′, G).
Venation of the _Cladophlebis_ type (cf. fig. 256, A).
It is not always easy to distinguish _Todites Williamsoni_ from
_Cladophlebis denticulata_, another common Jurassic fern, but in the
latter the pinnules are usually longer and relatively narrower and
the rachis is more slender (cf. fig. 256, B and 257). Schenk[800] and
Raciborski[801] have shown that the sporangia of _Todites_ conform
in the absence of a true annulus to those of _Todea_ (fig. 256, G)
and _Osmunda_. Nathorst[802] has recently figured a group of spores
of _Todites Williamsoni_ in illustration of the use of the treatment
of carbonised impressions with nitric acid and potassium chlorate.
This species, though widely distributed in Jurassic rocks, is hardly
distinguishable from the German Rhaetic fronds figured by Schenk from
Bayreuth as _Acrostichites Goeppertianus_[803], or from other fossils
referred to an unnecessarily large number of species by Fontaine[804]
from Upper Triassic rocks of Virginia[805].
It would seem from the paucity of later records of Osmundaceae that
the family reached its zenith in the Jurassic era. When we pass to
the later Tertiary and more recent deposits evidence is afforded in
regard to the geographical range of _Osmunda regalis_. It has been
shown to occur in the Pliocene forest-bed of Norfolk[806] as well as in
Palaeolithic and Neolithic deposits[807].
[Illustration: FIG. 257. _Cladophlebis denticulata._ (From a specimen
in the British Museum from the Inferior Oolite rocks of Yorkshire.
Slightly reduced.)]
A fertile frond from the Molteno (Rhaetic) beds of South Africa
referred to _Cladophlebis_ (_Todites_) _Roesserti_ (Presl)[808]
represents in all probability an Osmundaceous fern closely allied to
_Todites Williamsoni_. The same species is described by Zeiller[809]
from Rhaetic rocks of Tonkin and very similar types are figured by
Leuthardt[810] from Upper Triassic rocks of Basel as _Pecopteris
Rutimeyeri_ Heer, and by Fontaine[811] from rocks of the same age in
Virginia.
_Cladophlebis._
The generic name _Cladophlebis_ was instituted by Brongniart for
Mesozoic fern fronds characterised by ultimate segments of linear or
more or less falcate form attached to the pinnae by the whole of the
base, as in the Palaeozoic genus _Pecopteris_, possessing a midrib
strongly marked at the base and dividing towards the distal end of the
lamina into finer branches and giving off secondary forked and arched
veins at an acute angle. The term is generally restricted to Mesozoic
fern fronds which, on account of the absence or imperfection of fertile
pinnae, cannot be safely assigned to a particular family. In the case
of the species described below, the evidence in regard to systematic
position, though not conclusive, is sufficiently strong to justify its
inclusion in the Osmundaceae.
_Cladophlebis denticulata_ Brongniart. Figs. 256, A; 257, 258.
1828. _Pecopteris denticulata_[812], Brongniart, Prodrome, p. 57;
Hist. vég. foss. p. 301, Pl. XCVIII. figs. 1, 2.
— _P. Phillipsii_, Brongniart, Hist. p. 304, Pl. CIX. fig. 1.
This species is often confused[813] with _Todites Williamsoni_. The
name _Pecopteris whitbiensis_ has been used by different writers for
Jurassic fronds which are undoubtedly specifically distinct: specimens
so named by Brongniart should be referred to _Todites Williamsoni_,
while _P. whitbiensis_ of Lindley and Hutton[814] is Brongniart’s
_Cladophlebis denticulata_. It is impossible to determine with accuracy
the numerous examples described as _Pecopteris whitbiensis_, _Asplenium
whitbiense_, _Cladophlebis Albertsii_ (a Wealden species[815]),
_Asplenium_, or _Cladophlebis_, _nebbense_[816], etc., from Jurassic
and Rhaetic strata. The _Cladophlebis denticulata_ form of frond is one
of the commonest in recent ferns; it is represented by such species as
_Onoclea Struthopteris_, _Pteris arguta_, _Sadleria sp._, _Gleichenia
dubia_, _Alsophila lunulata_, _Cyathea dealbata_, and species of
_Polypodium_. It is, therefore, not surprising to find records of this
Mesozoic species from many localities and horizons. All that we can do
is to point out what appear to be the most probable cases of identity
among the numerous examples of fronds of this type from Mesozoic rocks,
particularly Rhaetic and Jurassic, in different parts of the world.
The name _Cladophlebis denticulata_ may be employed in a comprehensive
sense for fronds showing the following characters:—
Leaf large, bipinnate, with long spreading pinnae borne on a
comparatively slender rachis. Pinnules, in nearly all cases,
sterile, reaching a length of 3–4cm., acutely pointed, finely
denticulate or entire, attached by the whole of the base (fig.
257). In the apical region the pinnules become shorter and broader.
Venation of the _Cladophlebis_ type (fig. 256, A). Fertile pinnules
rather straighter than the sterile, characterised by linear sori
parallel to the lateral veins (fig. 258).
In endeavouring to distinguish specifically between fronds showing a
general agreement in habit with _C. denticulata_, special attention
should be paid to venation characters, the shape of the pinnules,
the relation of the two edges of the lamina to one another, and to
the amount of curvature of the whole pinnule. Unless the material is
abundant, it is often impossible to distinguish between characters of
specific value and others which are the expression of differences in
age or of position on a large frond, to say nothing of the well-known
variability which is amply illustrated by recent ferns. It is
remarkable that very few specimens are known which throw any light on
the nature of the fertile pinnae. Fig. 258 represents an impression
from the Inferior Oolite rocks of the Yorkshire coast in which the
exposed upper surface of the pinnules shows a series of parallel ridges
following the course of the lateral veins and no doubt formed by
oblong sori on the lower surface. There can be little doubt that the
specimen figured by Lindley and Hutton and by others as _Pecopteris
undans_[817] is, as Nathorst suggests, a portion of a fertile frond of
_C. denticulata_. A fertile specimen of a frond resembling in habit
_C. denticulata_, which Fontaine has described from the Jurassic
rocks of Oregon as _Danaeopsis Storrsii_[818], exhibits, as that
author points out, a superficial resemblance to the specimen named by
Lindley and Hutton _Pecopteris undans_. There is, however, no adequate
reason for referring the American fragment to the Marattiaceae. In the
absence of sporangia we cannot speak confidently as to the systematic
position of this common type; but there are fairly good grounds for
the assertion that some at least of the fronds described under this
name are those of Osmundaceae. The English specimen shown in fig.
258 is very similar to some Indian fossils figured by Feistmantel
as _Asplenites macrocarpus_[819], which are probably identical with
_Pecopteris australis_ Morris[820], a fern that is indistinguishable
from _Cladophlebis denticulata_. Renault[821] figured a fertile
specimen of the Australian fossil as _Todea australis_, which agrees
very closely with that shown in fig. 258, and the sporangia figured
by the French author are of the Osmundaceous type. Another example
of a fertile specimen is afforded by a Rhaetic fern from Franconia,
_Asplenites ottonis_, which is probably identical with _Alethopteris
Roesserti_ Presl [= _Cladophlebis_ (_Todites_) _Roesserti_], a plant
closely resembling _Cladophlebis denticulata_. Another argument in
favour of including _C. denticulata_ in the Osmundaceae is supplied
by the association of pinnae of this type with the petrified stem of
_Osmundites Dunlopi_ recorded by Kidston and Gwynne-Vaughan.
[Illustration: FIG. 258. Fertile pinnae of _Cladophlebis denticulata_.
(From a Yorkshire specimen in the Sedgwick Museum, Cambridge.)]
=Schizaeaceae.=
Evidence bearing on the existence of this family in Carboniferous
floras is by no means decisive. The generic name _Aneimites_ proposed
by Dawson[822] for some Devonian Canadian plants resembling species of
the recent genus _Aneimia_, and adopted by White[823] for a species
from the Pottsville beds of Virginia, is misleading. The Canadian
plants give no indication of the nature of the reproductive organs, and
the fronds described by White are, as he shows, those of a Pteridosperm
and bore seeds.
An examination of the suspiciously diagrammatic drawings published by
Corda[824] of the small fertile pinnules of a Carboniferous fern from
Bohemia, which he named _Senftenbergia elegans_, leads us to conclude
that the sporangia are almost certainly those of a Schizaeaceous
species. The small linear pinnules bear two rows of sessile sporangia,
singly as in recent Schizaeaceae and not in sori, characterised by
4–5 rows of regular annular cells (fig. 270, A) surrounding the apex.
It has already been pointed out that the apical annulus of recent
Schizaeaceae, though normally one row deep, may consist in part at
least of two rows. Zeiller[825] examined specimens of Corda’s species
and decided in favour of a Schizaeaceous affinity; he describes the
sporangia as 0·85–0·95 mm. in length, with 3 to 5 and occasionally only
two rows of cells in the apical annulus. Zeiller’s figures (fig. 270,
A) confirm the impression that Corda’s drawings are more beautiful than
accurate. Stur[826], on the other hand, who first pointed out that the
type-specimens of _Senftenbergia_ came from the Radnitz beds of Bohemia
and not from the Coal-Measures, convinced himself that the sporangia
have no true annulus (fig. 270, E). He describes them as characterised
by a comparatively strong wall and by the presence of a band of narrow
vertical cells marking the line of dehiscence, features which lead
him to assign the plant to the Marattiales, a group which seems to
have exercised a dominating influence over his judgment. In a later
publication Zeiller[827] replies to Stur’s criticism but adheres to
his original opinion. Solms-Laubach[828], while expressing himself in
favour of Marattiaceous affinity, recognises that Zeiller’s arguments
cannot be set aside.
The question must remain open until further evidence is forthcoming;
but it would seem that this Carboniferous type, not as yet recognised
in Britain, possessed sporangia having a distinct resemblance to those
of the Schizaeaceae, though this similarity does not amount to proof of
the existence of the family in the Palaeozoic era.
Palaeozoic floras may be described as rich in generalised types,
types foreshadowing lines of evolution, which in the course of ages
led to a sorting and a redistribution of characters. It may be that
_Senftenbergia_ is one of these generalised types.
• • • • •
It is not until we ascend the geological series as far as the older
Jurassic rocks that we meet with a type which can with confidence be
classed with the Schizaeaceae, as least so far as sporangial characters
are concerned. The species _Klukia exilis_ is selected as the best
known and most widely-spread representative of Jurassic Schizaeaceae.
_Klukia exilis_ (Phillips)[829]. Fig. 259.
The generic name _Klukia_ was proposed by Raciborski[830] for a species
originally described by Phillips[831] from the Inferior Oolite of
the Yorkshire coast as _Pecopteris exilis_. Bunbury’s[832] discovery
(supplemented by additional evidence obtained by Raciborski) of
well-preserved sporangia justified the substitution of a distinctive
designation for the provisional term _Pecopteris_.
[Illustration: FIG. 259. _Klukia exilis_ (Phillips). (Figs. 1–3, × 40;
fig. 4, × 3; fig. 5, nat. size.)]
The species may be defined as follows:—
Frond tripinnate, of the _Cladophlebis_ type; pinnae linear,
lanceolate, attached to the rachis at a wide angle. Ultimate
segments short and linear, entire or, in the lower part of a frond,
crenulate, 5 mm. long or occasionally longer. Sporangia 0·5 mm. in
length, borne singly on the lower surface of the lamina in a row on
each side of the midrib.
A re-examination[833] of the specimen described by Bunbury confirmed
his account of the structure of the sporangia. The pinna shown in
fig. 259 is characterised by unusually small fertile pinnules some
of which bear 10 sporangia in two rows; the annulus includes about
14 cells. Fertile specimens of this and similar forms are figured by
Raciborski[834] from Jurassic rocks of Poland, and good examples of the
English species may be seen in the Leckenby collection, Cambridge, in
the British Museum, the museums of Manchester, Scarborough, and other
places.
It is possible that specimens referred to _K. exilis_ by Yokoyama[835]
from Wealden strata in Japan may afford evidence of the persistence
of the species beyond the Jurassic era, but in view of the close
resemblance of the sterile fronds described from Wealden strata as
_Cladophlebis Brownii_[836] and _C. Dunkeri_[836] to those of _Klukia
exilis_, identity can be established only by an examination of fertile
specimens. A Jurassic fern recently described by Yabe[837] from Korea
as _Cladophlebis koraiensis_ may be identical with _K. exilis_ and
there is little doubt as to the existence of the species in Jurassic
Caucasian strata[838].
[Illustration: FIG. 260. _Ruffordia Goepperti_. (A, C, sterile; B,
fertile; slightly reduced. Specimens from the Wealden of Sussex;
British Museum; V. 2333, V. 2160, V. 2166.)]
_Ruffordia Goepperti_ (Dunk.). Fig. 260.
This Wealden fern[839] has been doubtfully assigned to the Schizaeaceae
on the ground of the resemblance of the sterile fronds to those of some
species of _Aneimia_, and because of the difference between the sterile
and fertile pinnae (Fig. 260). _Ruffordia_ cannot be regarded as a well
authenticated member of the Schizaeaceae.
[Illustration: FIG. 261.
A, A′. _Chrysodium lanzaeanum._
B, B′. _Lygodium Kaulfussi._
C. _Marattia Hookeri._
(After Gardner and Ettingshausen; A, B, ¾ nat. size.)]
_Lygodium Kaulfussi_, Heer. Fig. 261, B, B′.
Fragments of forked pinnules, agreeing very closely in venation and
general appearance with recent species of _Lygodium_, have been
identified by Gardner and Ettingshausen[840] from English Eocene beds
and by Knowlton from the Miocene beds of the Yellowstone Park[841]
as _Lygodium Kaulfussi_ Heer (fig. 261, B). Despite the absence of
sporangia it is probable that these fragments are correctly referred
to the Schizaeaceae. The sterile and fertile specimens figured by
Heer[842] from Tertiary beds of Switzerland agree very closely with
recent examples of _Lygodium_. Similar though perhaps less convincing
evidence of the existence of this family in Europe is furnished by
Saporta[843], who described two Eocene species from France.
=Gleicheniaceae.=
The application by Goeppert[844] and other earlier writers of the
generic name _Gleichenites_ to examples of Palaeozoic ferns was not
justified by any satisfactory evidence. One of Goeppert’s species,
_Gleichenites neuropteroides_, is identical with _Neuropteris
heterophylla_[845], a plant now included in the Pteridosperms.
The resemblance of sporangia and sori, whether preserved as carbonised
impressions or as petrified material, from Carboniferous rocks, to
those of recent species of Gleicheniaceae is in many cases at least the
result of misinterpretation of deceptive appearances. Williamson[846]
drew attention to the Gleichenia-like structure of some sections of
sporangia from the English Coal-Measures, but he did not realise the
ease with which sections of Marattiaceous sporangia in different planes
may be mistaken for those of annulate (leptosporangiate) sporangia.
In the regular dichotomous habit of Carboniferous fronds described as
species of _Diplothmema_ (Stur) and _Mariopteris_ (Zeiller)[847] we
have a close correspondence with the leaves of _Gleichenia_, but the
common occurrence of dichotomous branching among ferns is sufficient
reason for regarding this feature as an untrustworthy criterion of
relationship. It is, however, interesting to find that in addition
to the existence of some Upper Carboniferous ferns with sori like
those of recent Gleichenias, the type of stelar anatomy illustrated
by _Gleichenia dicarpa_ (fig. 237, C, p. 310) and other species is
characteristic of the primary structure of the stem of the Pteridosperm
_Heterangium_. We find in Carboniferous types undoubted indications of
anatomical and other features which in succeeding ages became the marks
of Gleicheniaceae.
Some Carboniferous fronds with short and small pinnules of the
_Pecopteris_ type, bearing sori composed of a small number of
sporangia, have been assigned by Grand’Eury and other authors to the
Gleicheniaceae; the same form of sorus is met with also on fronds with
Sphenopteroid segments. The former is illustrated by _Oligocarpia
Gutbieri_[848] and the latter by _O. Brongniarti_ described by Stur
and by Zeiller[849]. Zeiller has described the circular sori of
_Oligocarpia_ (fig. 270, B) as consisting of three to ten pyriform
sporangia borne at the ends of lateral veins and possessing a complete
transverse annulus, but Stur[850] believes that the annulus-like
appearance is due to the manner of preservation of exannulate
sporangia. In this opinion Stur is supported by Solms-Laubach[851]
and by Schenk[852]. Despite an agreement between _Oligocarpia_
and _Gleichenia_, as regards the form of the sori and the number
of sporangia, it is not certain that the existence of a typical
Gleicheniaceous annulus has been proved to occur in any Palaeozoic
sporangia[853].
From Upper Triassic beds of Virginia, Fontaine has figured several
fronds for which he instituted the genus _Mertensides_[854]. The habit,
as he points out, is not dichotomous, but the sori are circular and
are said to be composed in some species of four to six sporangia. No
satisfactory evidence is brought forward in support of the use of a
designation implying a close relationship with recent Gleichenias
(sect. _Mertensia_). One of the species described by Fontaine was
originally named by Bunbury _Pecopteris bullatus_[855], the imperfect
type-specimen of which is now in the Museum of the Cambridge Botany
School. In the form of the frond, the thick rachis, and in the pinnules
this Triassic species resembles _Todites Williamsoni_, but the
resemblance does not extend to the sori. Two of Fontaine’s species are
recorded by Stur from Austria[856], but he places them in the genus
_Oligocarpia_ and includes them in the Marattiaceae.
Leuthardt[857] figures what appears to be a Gleicheniaceous fern from
the Upper Triassic beds of Basel as _Gleichenites gracilis_ (Heer)
showing sori composed of five sporangia (fig. 265, C) with a horizontal
annulus. A Rhaetic species _Gleichenites microphyllus_ Schenk[858]
from Franconia agrees in the form of its small rounded pinnules with
_Gleichenia_, but no sporangia have so far been found.
An impression of a frond from Jurassic rocks of northern Italy figured
by Zigno as _Gleichenites elegans_[859] closely resembles in habit
recent species of _Gleichenia_; though no sporangia have been found,
the habit of the frond gives probability to Zigno’s determination.
A Jurassic species from Poland, _Gleichenites Rostafinskii_, referred
by Raciborski[860] to _Gleichenia_, exhibits a close agreement in habit
and in the form of the soral impressions to some recent species of
_Gleichenia_.
As we pass upwards to Wealden and more recent rocks it becomes clear
that the Gleicheniaceae were prominent members of late Mesozoic floras
in north Europe and reached as far north as Disco Island. In English
Wealden beds portions of sterile fronds have been found which were
assigned to a new genus _Leckenbya_[861], but it is probable that these
specimens would be more correctly referred to _Gleichenites_. Similarly
fragments of Gleichenia-like pinnae with very small rounded pinnules
occur in the Wealden rocks of Bernissart, Belgium[862], in north
Germany[863], and elsewhere. Conclusive evidence has been obtained by
Prof. Bommer of the existence of _Gleichenites_ in Wealden beds near
Brussels, where many plant remains have been found in a wonderful
state of preservation. The specimens, which I had an opportunity of
seeing some years ago, might easily be mistaken for rather old and
brown pieces of recent plants. Some of the Belgian fragments, of
which Prof. Bommer has kindly sent me drawings and photographs, are
characterised by an arrangement of vascular tissue identical with that
in the petioles and rhizomes of some protostelic Gleichenias. The stele
of one of the Belgian rhizomes appears to be identical with that of
_Gleichenia dicarpa_ (fig. 237, C. p. 310).
[Illustration: FIG. 262.
A. _Gleichenites longipennis_ Heer.
B. _G. delicatula_ Heer.
C. _G. Nordenskioldi_ Heer.
D. _G. Zippei_. (Corda.)
(After Heer; A, B, D, very slightly reduced.)]
_Gleichenites Zippei_ (Corda). Fig. 262, D.
This species, originally described by Corda as _Pecopteris Zippei_[864]
and afterwards figured by Heer[865] as _Gleichenia Zippei_ (fig. 262,
D) from Urgonian rocks of Greenland, affords a striking example of a
Mesozoic member of the _Gleicheniaceae_. It is characterised by the
dichotomous branching of the frond and by the occurrence of arrested
buds in the forks. The long and slender pinnae, reaching a length of 9
cm. and a breadth of 6–8 mm., bear small crowded pinnules occasionally
with circular sori which are described by Heer as consisting of a small
number of sporangia (cf. fig. 262, C). Several other Lower Cretaceous
species are recorded by Heer from Greenland, some of which are probably
unnecessarily separated from _Gleichenites Zippei_. Examples of these
are represented in fig. 262, A, B, C.
A Gleicheniaceous species described by Debey and Ettingshausen
from Lower Cretaceous rocks of Aix-la-Chapelle as _Didymosorus
comptonifolius_[866] is very similar in habit to some of Heer’s
Greenland species: this should probably be referred to the genus
_Gleichenites_.
_Gleichenites hantonensis_, Wank. Fig. 263.
From the Eocene beds of Bournemouth, Gardner and Ettingshausen[867]
have described under the name _Gleichenia hantonensis_ what is in all
probability a true _Gleichenia_ (fig. 263). This species, originally
recorded by Wanklyn[868], is characterised by a slender forked rachis
showing what may be traces of arrested buds between the arms of the
branches, by circular sori of six or eight sporangia and by the
presence of peculiar tendril-like appendages on the pinnae. If the
description of the tendrils is correct, this British species affords
one of the few instances of ferns adapted for climbing and may be
compared with the recent species _Davallia aculeata_ (fig. 232, p. 299).
=Matonineae.=
The genera _Laccopteris_ and _Matonidium_ may be described as examples
of Mesozoic ferns exhibiting a very close agreement with _Matonia_.
_Laccopteris_. This genus, founded by Presl[869], may be described as
follows:—
Frond pedate, in habit resembling _Matonia pectinata_, with
pinnate or pinnatifid pinnae; ultimate segments linear, provided
with a well-marked midrib giving off numerous dichotomously
branched secondary veins which are in places connected by lateral
anastomoses. Sori circular, forming a single row on each side of
the midrib (fig. 278, B); sporangia 5–15 in each sorus, with an
oblique annulus and tetrahedral spores. The presence of an indusium
is not certainly established.
[Illustration: FIG. 263. _Gleichenites hantonensis_ Wank. (Restoration,
after Gardner and Ettingshausen.)]
Schenk[870], who described several specimens of _Laccopteris_ from
Rhaetic rocks of Germany, compared the genus with _Gleichenia_ but
he also recognised the close resemblance to _Matonia pectinata_.
Zeiller[871] first established the practical identity of the sori and
sporangia of _Laccopteris_ and _Matonia_. The Rhaetic species, such as
_L. Muensteri_, _L. elegans_, and _L. Goepperti_, agree very closely
with _L. polypodioides_ and need not be described in detail.
[Illustration: FIG. 264. _Laccopteris elegans_ (Presl). (From a
specimen in the British Museum; from the Lower Keuper of Bayreuth,
Germany. Nat. size; part of pinnule × 3.)]
The Rhaetic species _Laccopteris elegans_, represented in fig. 264,
illustrates the characteristic habit of the genus and shows a feature
usually overlooked[872], namely the occurrence of anastomoses between
the lateral veins. The form of the sorus of another Rhaetic species is
shown in fig. 265, E. Schenk figures an interesting series of fronds of
_L. Goepperti_ in different stages of growth[873]; one of the younger
leaves is seen in fig. 265, D. An examination of Rhaetic specimens
of _Laccopteris_ in the Bergakademie of Berlin convinced me of the
correctness of the published descriptions of the sori.
[Illustration: FIG. 265.
A. _Matonidium Wiesneri._ (Slightly enlarged.)
B. _Marattiopsis marantacea._ (Slightly enlarged.)
C. _Gleichenites gracilis._ (Slightly enlarged.)
D. _Laccopteris Goepperti._ (Slightly reduced.)
E. _L. Muensteri._ (Enlarged.)
(A, after Krasser; B, C, after Leuthardt; D, E, after Schenk.)]
_Laccopteris polypodioides_ (Brongniart). Figs. 266–268; 278, A.
1828. _Phlebopteris polypodioides_[874], Brongniart, Hist. vég. foss.
p. 372, Pl. LXXXIII. fig. 1.
— _P. propinqua_, _ibid._ Pls. CXXXII. fig. 1, CXXXIII. fig. 2.
1829. _Pecopteris caespitosa_, Phillips, Geol. Yorks. p. 148,
Pl. VIII. fig. 10.
— _P. crenifolia_, _ibid._ Pl. VIII. fig. 10.
— _P. ligata_, _ibid._ Pl. VIII. fig. 14.
[Illustration: FIG. 266. _Laccopteris polypodioides_ (Brongn.). (× 14.)
(Brit. Mus.)]
In habit this species closely resembles _Matonia_ and _Matonidium_, the
long petiole divides distally into several spreading pinnatifid pinnae
with linear ultimate segments (fig. 278, A). Circular sori (indusiate?)
occur in a single row on each side of the midrib containing 12–14 large
sporangia (fig. 266) characterised by an obliquely vertical annulus.
The midrib of the pinnules gives off secondary veins at a wide angle
and these form a series of elongated meshes parallel to the median rib,
as in the recent genus _Woodwardia_; forked and anastomosing branches
are given off from these to the edge of the lamina (fig. 267).
[Illustration: FIG. 267. Pinnules of _Laccopteris_. (Enlarged.)
A, B. From the Inferior Oolite of Yorkshire.
C. From the Inferior Oolite of Stamford. (British Museum.)]
The specimen shown in fig. 268 is probably a young frond of this
species.
A very similar, possibly a specifically identical plant, was
described by Leckenby from English Jurassic rocks as _Phlebopteris
Woodwardi_[875], the distinguishing features of which are the greater
number of lateral veins and the smaller sori (fig. 267, A).
The name _Microdictyon_ was proposed by Saporta[876] for pinnules
differing slightly from those of _Laccopteris_ in venation characters:
he included _Laccopteris Woodwardi_ in this genus, but such differences
as are recognisable in the venation hardly justify the use of a
distinct generic title. Similarly, specimens described by Debey and
Ettingshausen[877] from Lower Cretaceous rocks of Aix-la-Chapelle as
species of _Carolopteris_ may also be included in _Laccopteris_.
[Illustration: FIG. 268. ? _Laccopteris polypodioides._ Nat. size. From
a specimen in the Whitby Museum (Brit. Mus.).]
_Laccopteris Dunkeri_ (Schenk)[878].
This species is represented in several Wealden localities by fragments
of fertile pinnae similar to those of _L. polypodioides_. It is almost
impossible to distinguish small specimens of the Wealden fern from
Heer’s genus _Nathorstia_ (Marattiaceae) unless the sori are well
preserved. This species occurs in Wealden beds in England, Germany,
Belgium, and elsewhere and has been discovered by Dr Marcus Gunn in
Upper Jurassic plant-beds of Sutherlandshire (N.E. Scotland).
• • • • •
_Laccopteris_ is widely spread in Rhaetic, Jurassic and Lower
Cretaceous floras. It affords evidence of the former abundance in
northern latitudes of a family now represented by the two species of
_Matonia_ confined to a restricted area in the southern hemisphere.
_Matonidium._
Schenk[879] instituted this convenient term for fossil fern fronds
agreeing in habit and in their sori with _Matonia pectinata_ (figs.
227, 228, p. 292). Zeiller[880] has drawn attention to the fact
that the Mesozoic species differ from the surviving types in the
greater number of sporangia in each sorus, and, it may be added,
in _Matonidium_ the fertile pinnules are more richly supplied with
sori than are those of _Matonia_. Unfortunately our knowledge of the
structure of the sporangia of _Matonidium_ is less complete than in the
case of _Laccopteris_, but such evidence as is available justifies the
conclusion that _Matonia_ is a direct descendant of ferns which formed
a prominent feature in European Jurassic and Wealden floras. It is
interesting to find that in a Cretaceous species, described by Krasser
(fig. 265, A) since the publication of Zeiller’s paper, the sori appear
to be identical in distribution and in appearance with those of the
recent species.
I am indebted to Prof. Bommer for permission to reproduce the
unpublished drawing represented in fig. 237 D (p. 310) of a section of
the rhizome of _Matonidium_ from the Belgian Wealden beds of Hainaut
(“Flore Bernissartienne”). The section shows an arrangement of vascular
tissue identical with that in the recent species: there may be two
solenosteles and in addition a solid axial strand. The form of the
leaf-trace in the fossil appears to be identical with that in _Matonia
pectinata_ (fig. 237, A, p. 310).
_Matonidium Goepperti_ (Ettingshausen)[881]. Fig. 269.
Under this name are included specimens from Inferior Oolite and Wealden
strata in Britain and elsewhere. It is, however, not impossible that if
more information were available, we should find adequate reasons for
recognising two specific types. Fontaine[882], adhering rigidly to the
rules of priority, speaks of this species as _Matonidium Althausii_
(Dunker), but Ettingshausen’s specific term is better known.
[Illustration: FIG. 269. _Matonidium Goepperti_ (Ettings.). (A, B, ½
nat. size; C, approximately nat. size.)]
Fronds pedate and apparently identical in habit with those of
_Matonia pectinata_; ultimate segments linear, slightly falcate and
bluntly pointed. Sori circular or oval, numerous, containing 15
to 20 sporangia with an oblique annulus, in two rows on the lower
surface of the pinnules; indusium as in _Matonia_.
The English examples have so far afforded no information in regard to
sporangial structure, but Schenk[883] has recognised a distinct annulus
in German material. In his description of fossil plants from Lower
Cretaceous rocks in California, Fontaine[884] doubtfully identifies
two very small fragments as _Matonidium Althausii_; the evidence is,
however, wholly inadequate.
_Matonidium Wiesneri_, Krasser[885]. Fig. 265, A.
This Cenomanian (Cretaceous) species from Moravia appears to be
identical in habit with the older type. The pinnules are larger and
bear fewer sori. Krasser’s figures of the sterile pinnules show no
lateral anastomosing between the secondary veins, but the small
vascular network below each sorus (fig. 265, A) is identical with that
in _Matonia pectinata_. The indusiate sori contain about six sporangia
with an oblique annulus.
The very wide geographical distribution of the Matonineae during the
Mesozoic era affords a striking contrast to the limited range of the
Malayan survivals.
=Hymenophyllaceae.=
The frequent use of the generic name _Hymenophyllites_ as a designation
of Palaeozoic ferns, more particularly in the older literature, is
another instance of the undue importance which palaeobotanists have
always been prone to attach to external resemblances of vegetative
organs. The fragment of lamina described by Stur for the Culm Measures
of Austria as _Hymenophyllum waldenburgense_[886] has no claim to
consideration as evidence of Palaeozoic Hymenophyllaceae. On the other
hand, there are a few records of fertile fronds which, though not to
be accepted without reserve, are worthy of more careful examination.
Some petrified sporangia described by Renault[887] from the Culm of
Esnost are referred to _Hymenophyllites_ on account of the position
of the annulus, which appears to encircle about two-thirds of the
circumference; it is, however, not certain that the annulus is
horizontal as in the recent genus.
The Culm species _Rhodea patentissima_ described by Ettingshausen[888]
as _Hymenophyllites patentissima_ and subsequently referred by
Stur[889] to _Rhodea_, is regarded by these authors as closely allied
to _Hymenophyllum_ simply on the ground of the finely divided and
delicate sterile fronds; another species, _Rhodea moravica_ (Ett.),
which Ettingshausen referred to _Trichomanes_, is compared with
recent species of that genus. In neither case do we know anything of
sporangial characters.
[Illustration: FIG. 270.
A, E. _Senftenbergia elegans._
B. _Oligocarpia Brongniartii._
C. _Trichomanes_ sp.
D. _Hymenophyllum tunbrigense._
F, G. _Sphenopteris_ (_Hymenophyllites_) _quadridactylites._
(A, B, F, G, after Zeiller; D, after Hooker; E, after Stur.)]
A fertile sphenopteroid frond figured by Schimper as _Hymenophyllum
Weissi_[890] from the Coal-Measures of Saarbrücken bears some
resemblance to recent Hymenophyllaceae, but the figures are by no means
convincing: an examination of the type-specimens in the Strassburg
Museum led Solms-Laubach[891] to express dissent from Schimper’s
determination. A more satisfactory example is that afforded by the
fertile pieces of a frond described by Zeiller[892] from French
Coal-Measures as _Hymenophyllites quadridactylites_ (Gutbier). Some
of the ultimate segments with a truncated tip are preserved in close
association with a group of oval sporangia with a complete transverse
annulus (fig. 270, F, G). The position of the sporangia is such as to
suggest their separation from a terminal columnar receptacle like that
in _Trichomanes_ and _Hymenophyllum_. In his account of this species
from the Coal-Measures of the Forest of Wyre, Kidston[893] states that
Zeiller informed him that he had noticed traces of what appeared to be
a columnar receptacle in the French specimens.
The records of Hymenophyllaceae from the Mesozoic and Tertiary
formations are not such as need detain us. The facts bearing on
the geological history of this family are singularly meagre. There
is no evidence which can be adduced in favour of regarding the
Hymenophyllaceae as ferns of great antiquity, which played a prominent
part in the floras of the past.
It is interesting to find that the genus _Ankyropteris_[894], one of
the Botryopterideae (a group of Palaeozoic Ferns for which I propose
the name Coenopterideae), has a morphological character in common
with _Trichomanes_, namely the production of axillary buds: there are
also features in the stelar anatomy shared by the Botryopterideae and
Hymenophyllaceae[895]. These resemblances, though by no means amounting
to proof of near relationship, point to a remote ancestry for certain
features retained by existing members of the Hymenophyllaceae.
=Cyatheaceae.=
The specimens from the Culm rocks of Moravia on which Stur founded the
species _Thyrsopteris schistorum_[896] are too imperfectly preserved
to warrant the use of this generic name. Goeppert[897] in 1836
instituted the genera _Cyatheites_, _Hemitelites_, and _Balantites_
for species of Carboniferous ferns believed to be closely allied to
recent Cyatheaceae, but a fuller knowledge of these types has clearly
demonstrated that in all cases the reference to this family had no
justification.
The Upper Carboniferous species _Dicksonites Pluckeneti_, of which
Sterzel[898] described fertile specimens in 1886 as possessing circular
sori, has since been shown by Grand’Eury[899] to be a Pteridosperm
bearing small seeds. In _Sphenopteris_ (_Discopteris_) _cristata_
(Brongn.) Zeiller[900] has described sori very like those of _Cyathea_
and _Alsophila_, but differing in the exannulate sporangia: this
species, like so many of the Palaeozoic ferns, is probably more akin to
the Marattiaceae than to the Cyatheaceae.
We have as yet no satisfactory evidence of the existence of the
Cyatheaceae in Palaeozoic floras. It is not until we reach the Jurassic
period that trustworthy data are obtained. Raciborski[901] has
identified as Cyatheaceous fertile Jurassic fronds from Poland, but
his figures are inconclusive. In _Alsophila polonica_ it is not clear
whether the annulus is vertical or oblique, and in another supposed
member of the family, _Gonatosorus Nathorsti_, in which the indusium is
described as bivalvate, there is no proof of affinity to Cyatheaceae.
In attempting to decipher the past history of the Cyatheaceae it
is important to remember the close resemblance between the fertile
segments of some species of _Davallia_ (Polypodiaceae) and those of
_Dicksonia_ (fig. 229, C, D, p. 294). Unless the sporangia are well
enough preserved to show the position of the annulus, it is frequently
impossible to feel much confidence in the value of the grosser
features, such as the reduced lamina of the fertile segments and the
form of the sori. It is, however, probable that the widely-spread
Jurassic species _Coniopteris hymenophylloides_ is correctly referred
to the Cyatheaceae, but even in the case of this species the evidence
of external form needs confirmation by an examination of individual
sporangia.
_Coniopteris._
This genus was instituted by Brongniart[902] for fossil fronds
characterised by pinnules more or less intermediate between the
_Pecopteris_ and _Sphenopteris_ type and agreeing in the form of the
sori with the leaves of recent species of _Dicksonia_. It should
be noted that Stur included in this genus a species, _Coniopteris
lunzensis_[903] from the Upper Trias of Lunz, which he regarded as a
Marattiaceous fern.
_Coniopteris hymenophylloides_, Brongn. Figs. 271, 272, 275, B.
1828. _Sphenopteris hymenophylloides_, Brongniart, Hist. vég. foss.
p. 189, Pl. LVI. fig. 4.
1829. _S. stipata_, Phillips, Geol. York. p. 147, Pl. X. fig. 8.
1835. _Tympanophora simplex_, Lindley and Hutton, Foss. Flor. Pl.
CLXX. A.
— _T. racemosa_, _ibid._ Pl. CLXX. B.
— _Sphenopteris arguta_, _ibid._ Pl. CLXVIII.
1836. _Hymenophyllites Phillipsi_, Goeppert, Foss. Farn. p. 256.
1849. _Coniopteris hymenophylloides_, Brongniart, Tableau, p. 105.
— _Coniopteris Murrayana_, _ibid._
1851. _Sphenopteris nephrocarpa_, Bunbury, Quart. Journ. Geol. Soc.
Vol. VII. p. 129, Pl. XII. fig. 1.
1876. _Thyrsopteris Murrayana_, Heer, Flor. Foss. Arct. Vol. IV. (2)
p. 30, Pls. I. II. VIII.
The above list represents a small selection of the names applied to
Jurassic ferns from different localities which there are good grounds
for regarding as referable to a single type[904].
Frond tripinnate; pinnae linear acuminate, attached to the rachis
at a wide angle; the pinnules vary considerably in size and
shape; in some the lamina is divided into a few broad and rounded
lobes (fig. 275, B) while in others the leaflets are dissected
into narrow linear segments. The sori are borne at the ends of
veins; the fertile pinnules have a much reduced lamina and, in
extreme cases, bear a close resemblance to those of _Thyrsopteris
elegans_ (fig. 229, A, p. 294). The sori are partially enclosed in
a cup-like indusium and the sporangia appear to have an oblique
annulus.
Venation and habit of frond of the _Sphenopteris_ type.
[Illustration: FIG. 271. _Coniopteris hymenophylloides_ (Brongn.).
Nat. size. From a specimen in the Manchester Museum.]
The pinna shown in fig. 271 is the type-specimen of _Sphenopteris
arguta_ Lind. and Hutt. from the Yorkshire Inferior Oolite and is
indistinguishable from the English examples on which Brongniart founded
his species _S. hymenophylloides_. Fig. 272 shows a specimen from
the York Museum illustrating the difference between the sterile and
fertile pinnae. The resemblance of some fertile pinnae of _Coniopteris
hymenophylloides_ to those of _Thyrsopteris elegans_ has led to a
frequent use, without any solid justification, of the generic name of
the Juan Fernandez fern for Jurassic and Wealden plants. It is not
impossible that some of the fossils described by Heer from Jurassic
rocks of Siberia[905] as species of _Thyrsopteris_ are Cyatheaceous
ferns, but it is impossible to say with certainty that they are
generically identical with the recent species. In his monograph of the
Potomac flora of Virginia[906] and Maryland, Fontaine has described as
species of _Thyrsopteris_ several specimens of fronds which afford
no evidence as to the nature of the sori or sporangia. Some of the
fronds referred by this author to _Thyrsopteris rarinervis_[907],
which I examined in the Washington Museum, are in all probability
examples of _Onychiopsis_, a genus included in the Polypodiaceae. The
fragments described by Lester Ward[908] as species of _Thyrsopteris_
from the Lower Cretaceous of the Black Hills of North America afford
no satisfactory evidence of relationship to the recent type. Similarly
Velenovský has described a Lower Cretaceous _Onychiopsis_ from
Bohemia[909] as a species of _Thyrsopteris_, although the fertile
segments bear little or no resemblance to those of the Cyatheaceous
genus. Some fertile portions of fronds described by Heer[910] as
_Asplenium Johnstrupi_ and afterwards as _Dicksonia Johnstrupi_[911]
from the Cretaceous beds (Kome series) of Greenland are very similar to
_Coniopteris hymenophylloides_.
[Illustration: FIG. 272. _Coniopteris hymenophylloides._ Specimen from
the Inferior Oolite, Scarborough; in the York Museum. [M.S.]]
_Coniopteris quinqueloba_ (Phillips). Fig. 273.
This species, originally described by Phillips[912] as _Sphenopteris
quinqueloba_, is very similar in habit to _C. hymenophylloides_,
differing chiefly in the smaller size of the leaf and in the narrower
ultimate segments. The specimen shown in fig. 273, B, illustrates the
form of the sorus and sporangia.
[Illustration: FIG. 273. _Coniopteris quinqueloba_ (Phillips). A, × 2;
B, considerably enlarged. From drawings supplied by Dr Nathorst.]
_Coniopteris arguta_ (Lind. and Hutt.[913]). Figs. 274, 275, A.
The sterile pinnae of this species bear pinnules of a type met with
in various species of ferns from different horizons; the smaller ones
are entire and slightly falcate, while on the lower part of a frond
the ultimate segments are longer and have a crenulate margin. The
fertile pinnae bear pinnules reduced to a midrib with a narrow border,
and terminating in a cup-like indusium (fig. 275, A). In habit the
sterile leaf (fig. 274) of this species is similar to the Jurassic
Schizaeaceous fern _Klukia exilis_.
_Protopteris._
Presl[914] instituted this genus for a Lower Cretaceous tree-fern
from Bohemia originally figured as _Lepidodendron punctatum_[915]
and assigned to a Palaeozoic horizon; it was afterwards named by
Corda[916] _Protopteris Sternbergii_ and referred by Brongniart[917]
to _Sigillaria_. The genus _Protopteris_ stands for fossil fern-stems
with the habit and, in the main, the structural features of recent
tree-ferns. Persistent leaf-bases and sinuous adventitious roots
cover the surface of the stems: the vascular system is of the
dictyostelic type characteristic of _Cyathea_ (fig. 240, p. 313) and
_Alsophila_. It is by the pattern formed by the vascular tissue on the
exposed surface of the leaf-bases that _Protopteris_ is most readily
recognised: the leaf-trace has a horse-shoe form with the ends curled
inwards and the sides more or less indented (fig. 277). The generic
name _Caulopteris_ is used by some authors in preference to Presl’s
genus; but _Protopteris_ is more conveniently restricted to Mesozoic
Cyatheaceous stems and _Caulopteris_ to Palaeozoic stems, with the
internal structure of _Psaronius_ (see Chap. XXIII.). Stenzel applies
_Caulopteris_ to Mesozoic stems in which the leaf-trace consists of
several separate strands and not of a continuous band.
[Illustration: FIG. 274. _Coniopteris arguta._ (Nat. size. From a
specimen in the Sedgwick Museum, Cambridge.)]
[Illustration: FIG. 275.
A. _Coniopteris arguta._ (Fertile pinnae; nat. size.)
B. _C. hymenophylloides._
A, from the Inferior Oolite of Yorkshire (British Museum); B, from
Jurassic rocks in Turkestan. ]
Lower Cretaceous casts of tree-fern stems in the Prague Museum have
been described under the names _Alsophilina_ and _Oncopteris_; the
figures of the latter (fig. 276) given by Feistmantel[918] and by
Velenovský[919] show the petiole-bases arranged in vertical rows and
characterised by leaf-traces consisting of two separate strands in the
form of two =V=s lying on their sides.
Tree-fern stems described under various generic names are not
infrequently found in European Lower Cretaceous rocks: their
comparative abundance affords an example of striking changes in
geographical distribution since the latter part of the Mesozoic epoch.
The Cyatheaceae no longer exist in Europe and the arborescent species
of the genus have retreated to more southern regions.
[Illustration: FIG. 276. _Oncopteris Nettvalli._ (After Velenovský; ¾
nat. size.)]
[Illustration: FIG. 277. _Protopteris punctata._ (After Heer; very
slightly reduced.)]
_Protopteris punctata_ (Sternb.). Fig. 277.
The earliest information in regard to the anatomy of this widely
spread Lower Cretaceous fern we owe to Corda, who showed that the
species agrees in essentials with existing tree-ferns. The English
example described by Carruthers[920] from Upper Greensand beds in
Dorsetshire (now in the British Museum) shows only the external
features. The sandstone cast (14 cm. in diameter), of which a
portion is seen in fig. 277, was described by Heer from Disco Island
(Greenland) as a Carboniferous species[921], but afterwards correctly
assigned to the Cenomanian series[922] This species is recorded
also from the Lower Cretaceous of Bohemia by Frič and Bayer[923]
Among examples of petrified stems exhibiting a general agreement
with _Protopteris punctata_ are those described by Stenzel[924] from
Turonian rocks in Germany. In one of these, _Rhizodendron oppoliense_
Göpp., attention is drawn to branches given off from the stem stele
which have a solenostelic structure in contrast to the dictyostele of
the stem; also to the minute structure of the tracheae which appear to
have their ends perforated, a feature shown by Gwynne-Vaughan[925] to
be characteristic of the xylem elements of many ferns.
[Illustration: FIG. 278.
A. _Laccopteris polypodioides_, Brongn. [From a specimen (39275) in
the British Museum; slightly reduced.]
B. _L. Muensteri._
C. _Dicksonia_ (petiole stele).
D. _Onychiopsis Mantelli_ (fertile segments).
E. _Hausmannia Sewardi_ Richt.
F. _H. Kohlmanni_ Bicht.
G, H. _Protopteris Witteana_, Schenk. (x, xylem; R, roots.)
(B, after Schenk; E, F, after Richter.)]
_Protopteris Witteana_ Schenk[926] (fig. 278, G, H), a Wealden species
recorded from Germany and England, represents a closely allied or
possibly an identical type. The section of the stem (fig. H) shows the
narrow vascular bands, x, of a dictyostele similar to that of recent
Cyatheaceous tree-ferns and a form of meristele (fig. G, x) resembling
that of _P. punctata_. Adventitious roots are seen in section at R
(figs. G and H).
=Polypodiaceae.=
Sections of petrified sporangia from the English Coal-Measures
(_Pteridotheca_ sp.) occasionally exhibit a striking resemblance to
those of recent Polypodiaceae[927], but in the absence of material
in which it is possible to recognise the true orientation of the
sporangia, the exact position of the annulus is almost impossible to
determine. We have as yet no satisfactory evidence of the existence of
true Polypodiaceae in the Palaeozoic era. It is noteworthy that apart
from the absence of ferns which can reasonably be included in this
family, the anatomical features of the Botryopterideae (Coenopterideae)
and of the Cycadofilices or Pteridosperms do not foreshadow those
of Polypodiaceous ferns. On the other hand, as we have already
noticed, anatomical characters of such families as the Gleicheniaceae,
Hymenophyllaceae, and Schizaeaceae are met with in certain generalised
Palaeozoic types. These facts are perhaps of some importance as
supplying collateral evidence in favour of the relatively more recent
origin of the dominant family of ferns in modern floras.
[Illustration: Fig. 279.
A. _Adiantides antiques_ (Ett.). (½ nat. size.)
B. _A. Lindsayoides_ (Sew.). (B′ nat. size.)
(A, after Kidston.)]
The use of the generic name _Adiantites_ for fern-like fronds of
Lower Carboniferous age characterised by cuneate pinnules like
those of species of _Adiantum_, suggests an affinity which is in
all probability non-existent. It has been pointed out that this
generic name was applied in the first instance to the leaves of
the Jurassic plant _Ginkgo digitata_[928] and should, therefore,
be discarded. Schimper[929] used the designation _Adiantides_, and
Ettingshausen[930], more rashly than wisely, preferred _Adiantum_. The
specimens described by Kidston[931] as _Adiantides antiquus_ (Ett.)
(fig. 279, A) from the Carboniferous limestone of Flintshire are
portions of tripinnate fronds bearing cuneate segments with numerous
forked veins radiating from the contracted base of the lamina. It is
not improbable, in view of Dr White’s[932] discovery of seeds on a very
similar plant from the Pottsville beds of North America, that this
characteristic Lower Carboniferous genus is a Pteridosperm.
From Jurassic rocks in various parts of the world numerous fossils
have been described under the generic names _Aspidium_, _Asplenium_,
_Davallia_, _Polypodium_, and _Pteris_. In the great majority of
cases such records leave much to be desired from the point of view of
students who appreciate the dangers of relying on external similarity
between vegetative organs, and on resemblances founded on obscure
impressions of sori. The generic term _Woodwardites_[933], which
suggests affinity with the recent genus _Woodwardia_, has been used for
Rhaetic plants belonging to the Dipteridinae.
A plant described as _Adiantides Lindsayoides_ from Jurassic rocks
of Victoria[934], characterised by marginal sori which appear to
be protected by the folded-over edge of the leaflets, and by the
resemblance of the pinnules to those of recent species of _Lindsaya_,
may be a true Polypodiaceous fern; but in this case, as in many similar
instances, nothing is known of the structure of the sporangia. Some
sterile pinnae described by Yabe from Jurassic rocks of Korea as
_Adiantites Sewardi_[935] may perhaps be identical with the Australian
species.
In such a species as _Polypodium oregonense_ Font., from Jurassic rocks
of Oregon, the generic name is chosen because the “fructification seems
near enough to that of _Polypodium_ to justify the placing of the plant
in that genus[936].” But the fact that no sporangia have been found is
a fatal objection to this identification.
_Onychiopsis._
This generic name was instituted by Yokoyama[937] for a Japanese
Wealden species, previously described by Geyler[938] as _Thyrsopteris
elongata_, on the ground that, in addition to a similarity in habit of
the sterile fronds, the fertile pinnae present a close agreement to
those of the recent genus _Onychium_.
_Onychiopsis Mantelli_[939] (Brongn.). Figs. 278, D; 280, A and B.
The Japanese species _Onychiopsis elongata_ may perhaps be identical
with this common Wealden fern which, as Fontaine points out, should
be called _O. psilotoides_ if the rule of priority is to be observed
irrespective of long usage.
1824. _Hymenopteris psilotoides_, Stokes and Webb, Trans. Geol. Soc.
[ii.], Vol. I. p. 423, Pl. XLVI. fig. 7.
1828. _Sphenopteris Mantelli_, Brongniart, Hist. vég. foss. p. 170,
Pl. XLV. figs. 3–7.
1890. _Onychiopsis Mantelli_, Nathorst, Denksch. Wien Akad. Vol.
LVII. p. 5.
_Onychiopsis Mantelli_ may be defined as follows:—
Frond bipinnate, ovate lanceolate, rachis winged; pinnae
approximate, given off at an acute angle; pinnules narrow,
acuminate, with a single vein; the larger segments serrate and
gradually passing into pinnae with narrow ultimate segments.
Fertile segments sessile or shortly stalked, linear ovate,
sometimes terminating in a short awn-like prolongation.
The fertile segments (fig. 278, D) bear so close a resemblance to those
of species of _Onychium_ that it would seem justifiable to regard the
plant as a member of the Polypodiaceae. This fern is one of the most
characteristic members of the Wealden floras; it occurs in abundance
in the English Wealden, in Portugal, Germany, Belgium, Japan, Bohemia,
South Africa, and elsewhere. A piece of rhizome figured from the
English Wealden[940] is very similar to the creeping rhizomes of recent
species of Polypodiaceae. The English Wealden specimens shown in fig.
280, A and B, illustrate the difference in form presented by leaves
of this species; the smaller pinnae reproduced in fig. A are more
characteristic of the species than are those of the slightly enlarged
example represented in fig. 280, B.
[Illustration: FIG. 280. _Onychiopsis Mantelli._ (From Wealden
specimens in the British Museum; No. 13495 and No. V. 2615. A,
natural size; B, very slightly enlarged.)]
Among British Tertiary species referred to Polypodiaceae, it is
interesting to find what may well be an authentic record of a
fern closely allied to the recent tropical species _Acrostichum_
(_Chrysodium_) _aureum_. This Eocene species from Bournemouth is
described as _Chrysodium lanzaeanum_[941]. The frond is simply pinnate
and apparently coriaceous in texture, with lanceolate or oblong
lanceolate pinnules (fig. 261, A, A′, p. 350), differing from those of
_Acrostichum aureum_ in being sessile. A prominent midrib gives off
numerous anastomosing veins. No fertile pinnules have been found.
Specimens described by Forbes from the Eocene beds of the Island of
Mull as _Onoclea hebraidica_[942] bear a strong likeness to the North
American and Japanese recent species _Onoclea sensibilis_. Fertile
specimens referred to the latter species are recorded by Knowlton[943]
from Tertiary beds of Montana.
A species described by Saporta[944] from the Eocene of Sézanne as
_Adiantum apalophyllum_ is recorded by Gardner and Ettingshausen from
Bournemouth; an identification which is based on somewhat meagre
evidence.
The following remarks by Gardner and Ettingshausen are worthy of
repetition as calling attention to circumstances often overlooked in
analyses of fossil floras. They speak of ferns as relatively rare
in British Eocene rocks and add,—“the floras consist principally of
deciduous dicotyledonous leaves, which ... fell into the water and
were tranquilly silted over. Ferns, on the other hand, would require
some violence to remove them from the place of their growth, and their
preservation would consequently be exceptional, and they would be
mutilated and fragmentary. This may account for their rarity. Few as
the British ferns are in the number of species, they nevertheless form
the largest and most important series of Eocene ferns, even of Tertiary
ferns, yet described from one group of beds[945].”
=Dipteridinae.=
_Dictyophyllum._
This genus was founded by Lindley and Hutton for a pinnatifid leaf
from the Jurassic rocks of Yorkshire which they regarded as probably
dicotyledonous and named _D. rugosum_[946]. Several ferns of this genus
have since been found with well-preserved sori which demonstrate a
close similarity to the recent fern _Dipteris._ _Dictyophyllum_ may be
defined as follows:—
Fronds large and palmate, characterised by the equal dichotomy of the
main rachis into two arms which curve outwards and then bend inwards
(fig. 281); from the surface of each arm are given off numerous
spreading pinnae with a lamina more or less deeply dissected into
lobes varying in breadth and in the form of the apex. Each lobe has a
median vein, from which branches are given off approximately at right
angles and then subdivide into a reticulum, in the meshes of which the
veinlets end blindly (fig. 282, A and E). Sori composed of annulate
sporangia are crowded on the lower surface of the lamina. In habit
and in sporangial characters the genus closely resembles _Dipteris_,
and in the branching of the frond suggests comparison with _Matonia_.
The rhizome (_Rhizomopteris_) is creeping and dichotomously branched,
bearing leaf-scars with a horse-shoe form of vascular strand.
[Illustration: FIG. 281. _Dictyophyllum exile._ (After Nathorst; much
reduced.)]
_Dictyophyllum_ is represented by several types to which various
specific names have been assigned, the distinguishing features being
the form of the pinna lobes, the degree of concrescence between the
basal portions of the pinnae, and similar features which in some cases
can only be safely used as criteria when large specimens are available
for comparison.
_Dictyophyllum exile_ (Brauns). Figs. 281, 282, D, E.
1862. _Camptopteris exilis_, Brauns, Palaeontograph. IX. p. 54.
1867. _Dictyophyllum acutilobum_, Schenk, Foss. Flor. Grenz. p. 77,
Pls. XIX. XX.
1878. _D. exile_, Nathorst, Flora vid Bjuf, I. p. 39, Pl. V. fig. 7.
—— _D. acutilobum_, _ibid._ Pl. XI. fig. 1.
The restoration, after Nathorst[947], shown in fig. 281 illustrates the
habit of this striking fern, examples of which or of closely allied
species are recorded from Rhaetic rocks of Germany, Scania, Persia,
Bornholm, Tonkin, China, and elsewhere[948]. The petiole, reaching
a length of 60 cm., forks at the apex into two equal arms leaving
between them an oval space and occasionally crossing one another. The
axes of these branches are twisted so that the pinnae, which may be
as many as 24 on each arm, and arise from the inner side, by torsion
of the axes assume an external position. An interesting analogy as
regards the twisted rachis of _Dictyophyllum exile_ and _Camptopteris_
is afforded by the leaves of the Cycads, _Macrozamia Fawcettiae_ and
_M. corallipes_, which are also characterised by the torsion of the
rachis. The habit, justly compared by Nathorst with that of _Matonia
pectinata_, affords another illustration of the common occurrence
in older ferns of a dichotomous system of branching. The pinnae,
characterised by circinate vernation, reach a length of 60 cm. and are
divided into linear lobes inclined obliquely or at right angles to the
pinna axis. The whole of the under surface of the lamina may be covered
with sporangia, 4–7 sporangia in each sorus; the annulus is incomplete
and approximately vertical (fig. 282, D). The rhizome is probably
represented by the dichotomously branched axis described by Nathorst
from Scania as _Rhizomopteris major_; the leaf-scars show a horse-shoe
leaf-trace.
[Illustration: FIG. 282.
A. _Dictyophyllum Nilssoni._
B. _Rhizomopteris Schenki._
C. _Camptopteris spiralis._
D, E. _Dictyophyllum exile._
(After Nathorst; A, B, C, E, ⅔ nat. size.)]
_Dictyophyllum Nathorsti_ Zeiller[949].
This type, represented by a splendid series of specimens from
the Rhaetic beds of Tonkin, agrees very closely with _D. exile_.
It differs, however, in the basal parts of the pinnae which are
concrescent for a length of 5 to 8 cm. instead of free as in _D.
exile_; and, to a slight degree, in the form of the ultimate segments.
In habit and in soral characters the two species are practically
identical. Each sorus contains 5 to 8 sporangia, which are rather
larger than those of _Dipteris_.
_Dictyophyllum rugosum_, Lind. and Hutt. Fig. 283.
1828. _Phlebopteris Phillipsii_, Brongniart, Hist. vég. foss. p. 377,
Pl. CXXXII. fig. 3; Pl. CXXXIII. fig. 1.
1829. _Phyllites nervulosis_, Phillips, Geol. Yorks. p. 148, Pl.
VIII. fig. 9.
1834. _Dictyophyllum rugosum_, Lindley and Hutton, Foss. Flor. II.
Pl. CIV.
1836. _Polypodites heracleifolius_, Goeppert, Foss. Farn. p. 344.
1849. _Camptopteris Phillipsii_, Brongniart, Tableau, p. 105.
1880. _Clathropteris whitbyensis_, Nathorst, Berättelse, p. 83.
This species, which is characteristic of Jurassic rocks, is less
completely known than the two types described above, but in the form
and venation of the pinnae there is little difference between the
Rhaetic and Jurassic plants. The leaves of the Jurassic species appear
to have been smaller and more like those of _Dipteris conjugata_ (fig.
231); there are no indications of the existence of the two curved
arms at the summit of the petiole which form so striking a feature
in _D. exile_ and _D. Nathorsti_. No sporangia have been found on
English specimens, but it is safe to assume their agreement with those
of other species. A more complete list of records of _D. rugosum_ is
given in the first volume of the British Museum Catalogue of Jurassic
plants[950].
[Illustration: FIG. 283. _Dictyophyllum rugosum_ (Lind. and Hutt.).
(Brit. Mus. Nat. size.)]
Nathorst[951] has recently drawn attention to certain differences
between _Dictyophyllum_ and _Dipteris_. The pinnate division of the
pinnae is not represented in the fronds of the recent species, but this
method of lobing, which is a marked characteristic of _Dictyophyllum_,
is less prominent in _Clathropteris_; and in _Camptopteris lunzensis_
Stur[952], an Austrian Upper Triassic species, the pinnae are entire.
In _Dictyophyllum_ the sori cover the whole lower surface of the leaf;
in _Dipteris_ they are more widely separated and the sporangia have a
diameter of 0·02 mm., but in _Dictyophyllum_ the diameter is 0·4–0·6
mm. Moreover in _Dictyophyllum_ the sori contain 5 to 8 sporangia,
whereas in _Dipteris_ they are much more numerous. Despite these
differences it is clear, as Nathorst says, that _Dictyophyllum_,
_Clathropteris_, and _Camptopteris_ are existing types very closely
allied to _Dipteris_. It is a matter of secondary importance whether
we include all in the Dipteridinae or follow Nathorst’s suggestion and
refer the fossil genera to the separate family Camptopteridinae.
_Thaumatopteris._
This genus, founded by Goeppert[953] for a Rhaetic plant from Bayreuth,
is by some authors[954] regarded as identical with _Dictyophyllum_,
but it has recently been resuscitated by Nathorst[955] for specimens
which he names _T. Schenki_, formerly included by Schenk in his species
_T. Brauniana_[956]. It bears a close resemblance, in the long linear
pinnules with an entire or crenulate margin, to _Dictyophyllum Fuchsi_
described by Zeiller[957] from Tonkin, and it would seem hardly
necessary to adopt a distinctive generic designation. The sporangia
have a vertical or slightly oblique annulus and the rhizome is similar
to that of _Dictyophyllum exile_. The habit of the genus is shown in
fig. 284, which represents one of the German Rhaetic species.
[Illustration: FIG. 284. _Thaumatopteris Münsteri._ (From a specimen in
the Bergakademie, Berlin; ⅓ nat. size.)]
_Clathropteris._
_Clathropteris meniscoides_, Brongn. Fig. 285.
_Clathropteris_, founded by Brongniart[958] for Rhaetic specimens from
Scania, agrees very closely with some species of _Dictyophyllum_,
but in view of the more rectangular form of the venation-meshes it
is convenient to retain both names. The type-species was originally
named _Filicites meniscoides_[959] and afterwards transferred to
_Clathropteris_. An examination of Brongniart’s specimens has
convinced Nathorst of the specific identity of _C. meniscoides_ and _C.
platyphylla_. The Tonkin leaves described by Zeiller[960] under the
latter name should, therefore, be included in _C. meniscoides_, which
may be thus defined:
The petiolate frond is characterised by an equal dichotomy of
the rachis, as in _Dictyophyllum_; each branch bore 5–15 pinnae,
disposed _en éventail_, reaching a length of 20–30 cm. and fused
basally as in _D. Nathorsti_ Zeill. Pinnae linear lanceolate,
slightly contracted at the lower end and gradually tapered
distally. The lamina, 3–14 cm. broad, is characterised by obtusely
pointed marginal lobes. From the midrib of each pinna lateral
veins are given off at a wide angle, and adjacent veins are
connected by a series of branches which divide the lamina into a
regular reticulum of rectangular and polygonal meshes (fig. 285).
The sori are abundant and contain 5–12 sporangia like those of
_Dictyophyllum_.
[Illustration: FIG. 285. _Clathropteris meniscoides._ From Rhaetic
rocks near Erlangen. [M.S.]]
[Illustration: FIG. 286. _Clathropteris egyptiaca._ (Nat. size.) _a_,
_b_, pieces of main ribs in grooves.]
What is probably the rhizome of this species has been described
by Nathorst (_Rhizomopteris cruciata_); it is similar to that of
_Dictyophyllum_, but the leaf-scars are more widely separated. This
species occurs in Upper Triassic, Rhaetic or Lower Jurassic rocks of
Scania, France, Germany, Switzerland, Bornholm, North America, China,
Tonkin, and Persia and is represented by fragments in the Rhaetic beds
of Bristol[961].
_Clathropteris egyptiaca_ Sew.[962] Fig. 286.
The specimen on which this species was founded was discovered in the
Nubian Sandstone east of Edfu; the age of the beds is uncertain, but
the presence of _Clathropteris_ suggests a Lower Jurassic or Rhaetic
horizon[963]. Seven strong ribs radiate through the lamina from the
summit of the petiole; at _a_ and _b_ small pieces of the projecting
ribs are shown in the grooves. From the main veins slender branches are
given off at right angles and, as seen in the enlarged drawing, these
again subdivide into a delicate reticulum with free-ending veinlets.
[Illustration: FIG. 287. _Camptopteris spiralis._ (After Nathorst. Much
reduced.)]
_Camptopteris._
_Camptopteris spiralis_, Nath. Figs. 282, C; 287.
Nathorst proposed this generic name for Rhaetic fronds[964] resembling
those of _Clathropteris_ and _Dictyophyllum_, but differing in the
form of the pinnae and in habit. The habit of the type-species, _C.
spiralis_, is shown in fig. 287. An examination of the specimens in
the Stockholm Museum convinced me of the correctness of Nathorst’s
restoration[965]. Each of the forked arms of the rachis bore as many
as 150–160 long and narrow pinnae characterised by an anastomosing
venation (fig. 282, C) and by a spiral disposition due to the
torsion of the axes. The sporangia agree in essentials with those of
_Dictyophyllum_.
_Hausmannia._
A critical and exhaustive account of this genus has been given by Prof.
Von Richter[966] based on an examination of specimens found in the
Lower Cretaceous rocks of Quedlinburg in Germany. The name was proposed
by Dunker[967] for leaves from the Wealden of Germany characterised by
a deeply dissected dichotomously branched lamina. Andrae subsequently
instituted the genus _Protorhipis_[968] for suborbicular leaves with
dichotomously branched ribs from the Lias of Steierdorf. A similar
but smaller type of leaf was afterwards described by Zigno[969]
from Jurassic beds of Italy as _P. asarifolius_, and Nathorst[970]
figured a closely allied form from Rhaetic rocks of Sweden. While
some authors regarded _Hausmannia_ and _Protorhipis_ as ferns, others
compared them with the leaves of _Baiera_ (Ginkgoales); Saporta
suggested a dicotyledonous affinity for leaves of the _Protorhipis_
type. The true nature of the fossils was recognised by Zeiller[971],
who called attention to the very close resemblance in habit and in
soral characters to the recent genus _Dipteris_. A comparison of the
different species of _Dipteris_, including young leaves (fig. 231,
p. 297), with those of the fossil species reveals a very striking
agreement[972]. There can be no doubt, as Richter points out, that the
names _Hausmannia_ and _Protorhipis_ stand for one generic type.
_Hausmannia_ may be defined as follows:
Rhizome creeping, slender, dichotomously branched; leaf-stalks
slender (2–25 cm. long), bearing a leathery lamina (1–12 cm. long
and broad), wedge-shaped below, occasionally cordate or reniform,
entire or more or less deeply lobed into broad linear segments.
The leaf is characterised by dichotomously branched main ribs
which arise from the summit of the rachis as two divergent arms
and radiate in a palmate manner, with repeated forking, through
the lamina. Lateral veins are given off at a wide angle, and, by
subdivision, form a fairly regular network similar to that in
_Dictyophyllum_, _Clathropteris_, and _Dipteris_.
[Illustration: FIG. 288. _Hausmannia dichotoma._ (Specimens from
the late Dr Marcus Gunn’s Collection of Upper Jurassic plants,
Sutherlandshire; very slightly reduced.)]
_Hausmannia dichotoma_, Dunker[973]. Fig. 288, A, B.
This Wealden species, represented in the North German flora and in
beds of approximately the same age at Quedlinburg, has been discovered
by Dr Marcus Gunn in Upper Jurassic rocks on the north-east coast of
Scotland. The lamina (12 cm. or more in length) is divided into five
to seven linear segments and bears a close superficial resemblance
to leaves of _Baiera_ and to recent species of _Schizaea_ (fig. 222,
p. 287). Each segment contains one or two main ribs (fig. 288, A). A
similar form is described by Bartholin[974] and by Moeller[975] as _H.
Forchammeri_ from Jurassic rocks of Bornholm.
_Hausmannia Kohlmanni_, Richt. Fig. 278, F.
In this species, instituted by Richter from material obtained from the
Lower Cretaceous beds of Strohberg[976], the comparatively slender
rhizome bears fronds with petioles reaching a length in extreme cases
of 25 cm. but usually of about 10 cm. The lamina (1–7 cm. long and
1–10 cm. broad) is described as leathery, obcordate, and divided into
two symmetrical halves by a median sinus which, though occasionally
extending more than half-way through the lamina, is usually shallow.
The venation consists of two main branches which diverge from the
summit of the petiole (fig. 278, F) and subdivide into dichotomously
branched ribs; finer veins (not shown in the drawing) are given off
from these at right angles and form more or less rectangular meshes
as in other members of the Dipteridinae and in such recent ferns as
_Polypodium quercifolium_ (fig. 231, D, p. 297).
The imperfect lamina represented in fig. 289 may belong to _Hausmannia
Richteri_ or may be a distinct species; it shows some of the finer
veins connecting the shorter forked ribs, which formed part of the
reticulate ramifying system in the mesophyll. This specimen was
obtained from the plant-beds of Culgower on the Sutherlandshire coast,
which have been placed by some geologists in the Kimmeridgian series.
The smaller type represented in fig. 278, E, is referred by Richter
to a distinct species, _Hausmannia Sewardi_[977], founded on a few
specimens from the Lower Cretaceous strata of Strohberg. This species
is characterised by a stouter rhizome bearing smaller leaves consisting
of a short petiole (3–4 cm. long) and an obovate lamina (1–2 cm. long
and broad). There are usually two opposite leaflets on each leaf-stalk,
and these may be equivalent to the two halves of a single deeply
dissected lamina.
[Illustration: FIG. 289. _Hausmannia sp._ Upper Jurassic, near
Helmsdale, Scotland. From a specimen in the British Museum. (Nat.
size.)]
It is interesting to compare these different forms of _Hausmannia_ with
the fronds of recent species of _Dipteris_ represented in fig. 231. The
more deeply dissected type, such as _H. dichotoma_, closely resembles
_D. Lobbiana_ or _D. quinquefurcata_, while the more or less entire
fossil leaves (fig. 278, E, F and fig. 289) are very like the somewhat
unusual form of _Dipteris conjugata_ shown in fig. 231, B, p. 297.
Other species of the genus are recorded from Liassic rocks of
Steierdorf[978] (Hungary) and of Bornholm[979]. Nathorst[980] has
described a small Rhaetic species from Scania: a French Permian plant
described by Zeiller[981] and compared by him with _H. dichotoma_, may
be a Palaeozoic example of this Dipteris-like genus.
Some segments of leaves from the Eocene beds (Middle Bagshot) of
Bournemouth, and now in the British Museum, described by Gardner
and Ettingshausen[982] as _Podoloma polypodioides_, bear a close
resemblance in the venation to the lamina of _Dipteris conjugata_.