Ctenopteris.
This name was instituted by Saporta[1463], at Brongniart’s suggestion, for Liassic species characterised by pinnules like those of Thinnfeldia, but distinguished by the bipinnate habit of the frond. Saporta compares the genus with the Palaeozoic leaves known as Odontopteris, and with Italian Jurassic plants referred by Zigno to his genus Dichopteris.
The name Ctenozamites is applied by Nathorst[1464] to the type of frond which Saporta, Zeiller, and other authors refer to Ctenopteris. Nathorst instituted Ctenozamites for fossils agreeing in the form and venation of the pinnules with his genus Ptilizamites but differing in being bipinnate and not pinnate.
Fronds of Ctenopteris are characteristic of the Jurassic and Rhaetic series; they are known only in the sterile condition. As Zeiller[1465] says, Ctenopteris may be a member of the Cycadofilices, an extinct group founded on Palaeozoic plants combining Cycadean and Filicinean characters, and some of which are now known to be Pteridosperms. It is probable that the genus is not a true fern: it is more likely to be a member of the Cycadophyta or of some generalised extinct group.
Ctenopteris cycadea (Brongniart). Fig. 362.
- 1828. Filicites cycadea, Brongniart, Hist. Vég. foss. p. 387, Pl. CXXIX.
- 1832. Odontopteris cycadea, Berger, Verstein. Coburg Geg. p. 23, Pl. III.
- 1873. Ctenopteris cycadea, Saporta, Pal. Franç. Vol. I. p. 355, Pls. XL. XLI.
Frond bipinnate, broad rachis giving off branches at an acute angle; pinnules broadly linear, slightly falcate, with several slightly divergent forked veins.
A frond very similar to the Lower Lias specimen from Dorsetshire represented in [fig. 362] was described by Leckenby as Ctenis Leckenbyi (Bean MS.) from the Inferior Oolite of Yorkshire[1466]. Leckenby recognised the possibility of a Cycadean affinity, but regarded the bipinnate habit as an objection. The branched fronds of the Australian Cycad Bowenia supply an answer to this objection. Several good examples of Ctenopteris cycadea are figured by Schenk[1467] from Rhaetic rocks of Persia. Zeiller’s Tonkin Rhaetic species, C. Sarrani[1468], affords a striking illustration of the difficulty of drawing a clear line of separation between Ctenopteris and some species of Thinnfeldia.
Fig. 362. Ctenopteris cycadea, Brongn. (½ nat. size.) From a specimen in the British Museum. [M.S.]