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.

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.

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.

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.

Fig. 274. Coniopteris arguta. (Nat. size. From a specimen in the Sedgwick Museum, Cambridge.)

Fig. 275.

  1. Coniopteris arguta. (Fertile pinnae; nat. size.)
  2. 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 Vs 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.

Fig. 276. Oncopteris Nettvalli. (After Velenovský; ¾ nat. size.)

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.

Fig. 278.

(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).