CHAPTER XXIV.
Ophioglossales (Fossil).
The fossils hitherto classed with the Ophioglossales are not such as afford any satisfactory evidence in regard to the past history or phylogeny of the group. In the generalised class of Palaeozoic ferns, the Botryopterideae, we find certain characters suggesting comparison with recent members of the Ophioglossaceae, but no trustworthy records of these eusporangiate ferns are furnished by the older plant-bearing strata.
Fig. 301. Rhacopteris sp., Ballycastle, Ireland. From a specimen in the Manchester Museum. [M.S.]
The genus Rhacopteris ([fig. 301]), characteristic of the Culm flora, has been compared with Botrychium, but on grounds which are wholly inadequate. The species R. paniculifera Stur[1095] is characterised by a stout rachis bearing two rows of laterally attached rhomboidal or subtriangular segments with a more or less deeply lobed margin and spreading veins. The rachis branches distally into two arms, and these are again symmetrically subdivided into fertile axes bearing clusters of small spherical bodies 1 mm. broad, which Stur speaks of as exannulate sporangia similar to those of Botrychium. He includes the species in the Ophioglossaceae. As Zeiller[1096] pertinently remarks, Rhacopteris differs essentially in habit from any recent member of this family. Rhacopteris also includes species characterised by leaflets deeply dissected into linear segments; an example of this form is represented by Rhacopteris flabellata (Tate) recorded by Kidston[1097] from rocks of Calciferous Sandstone age in Flintshire.
The specimen described by Renault[1098] from the Carboniferous rocks of Autun as Ophioglossites antiqua is equally unconvincing: it consists of a carbonised fragment, 7 cm. × 1·5 cm., regarded as part of a fertile lamina characterised by a vertical series of transversely elongated slits, 7 mm. wide, some of which, on slight magnification, are seen to contain a mass of small orange-yellow granulations. The slits are compared with the surface-openings of the sunken sporangia of Ophioglossum, and the yellow bodies are identified as spores. The material is too imperfect to justify the use of the name Ophioglossites.
Noeggerathia.
This genus of uncertain position may be briefly described here, though it has little claim to recognition as a representative of the Ophioglossales. It is characteristic of Lower Carboniferous rocks and is compared by Stur[1099] with recent Ophioglossaceae. Noeggerathia foliosa Sternb. ([fig. 302]) may be cited as a typical example of the genus. It consists of an axis bearing ovate leaves with numerous spreading veins. The upper part of the axis forms a spike composed of fertile leaves in the form of transversely oval bracts 2 cm. broad with a serrate edge bearing on the upper face several sporangia (3 × 4 mm.) in some of which spores have been seen ([fig. 302], B, C). In another form described by Weiss[1100] the bracts bear a greater number of sporangia characterised by the presence of an arillus-like basal ring.
Fig. 302. Noeggerathia foliosa. (After Stur; A, reduced.) B, Fertile leaf; C, Sporangium.
Geinitz[1101], who first described fertile specimens of Noeggerathia, placed the genus in the Gymnosperms, and O. Feistmantel[1102] was in favour of this view. C. Feistmantel[1103], who described the small bodies in the sporangia, suggested comparison with Schizaeaceae, and Weiss[1104] discussed various possibilities, asking but not answering the question, are the so-called sporangia rightly so named or are they fruits? Potonié[1105] places the genus in the Cycadofilices. An important feature is the occurrence of the sporangia on the upper face of the bracts as in Lycopodiales and Sphenophyllum, but in other respects Noeggerathia bears no resemblance to these two groups. Sterile examples of the genus are similar in habit to Rhacopteris, but in the latter genus the leaves or leaflets are laterally attached and not obliquely inserted. Further, we may assume that in Rhacopteris the segments are leaflets of a compound leaf, whereas in Noeggerathia they are probably single leaves. We must leave the position of this Lower Carboniferous genus undecided, merely expressing the opinion that it is perhaps more nearly allied to the Cycads than to any other group.
Fig. 303. Chiropteris Zeilleri, Sew. [From a specimen in the British Museum (v. 3268). Nat. size.]
The plant figured by Lindley and Hutton from the English Coal-Measures as Noeggerathia flabellata, which some authors quote as a species of Noeggerathia, is generally recognised as a Psygmophyllum and placed with some hesitation in the Ginkgoales.
Chiropteris.
This genus was founded by Kurr on a leaf characterised by anastomosing venation from Keuper beds near Stuttgart. A resemblance in form and venation to the leaves of recent species of Ophioglossum led authors to suggest the inclusion of Kurr’s specimen in the Ophioglossaceae. We have, however, no justification for considering Chiropteris as a member of this family; it may be a fern, and that is all that can be said. The leaf represented in [fig. 303] is the type-specimen of a South African Rhaetic species Chiropteris Zeilleri[1106]. The genus is recorded also from Rhaetic rocks in Queensland.[1107]
Newberry[1108] describes some leaves from the Lower Cretaceous of Montana as species of Chiropteris: one of his types, C. spatulata, is almost certainly a Sagenopteris, similar to S. Phillipsi (figs. [327], [328]) or S. Mantelli. A second species, C. Williamsii, is probably not generically identical with the specimen represented in [fig. 303].