The specimen represented in [fig. 345] illustrates the characters of this commonest representative of the genus.
Fig. 345. Gangamopteris cyclopteroides, Feist. (Nat. size. From Arber, after Feistmantel.)
Gangamopteris kashmirensis, Seward.
- 1905. Seward, Mem. Geol. Surv. India, Vol. II. Mem. ii.
This type agrees closely with G. cyclopteroides in size and in the form of the leaf, but it is distinguished by the flatter form of the arch formed by the lateral veins, by their greater inclination to the margin of the lamina, and by the more acutely pointed apex of the lamina. This species, though not very sharply distinguished from G. cyclopteroides, is important as coming from beds which have been assigned on other than palaeobotanical evidence to an Upper or possibly a Middle Carboniferous horizon[1353].
We have no definite information in regard to the nature of the reproductive organs of Gangamopteris, but such evidence as there is supports the view expressed by Dr White[1354] and shared by some other authors that Gangamopteris and Glossopteris should be assigned to the Pteridosperms. Despite the abundance of Gangamopteris leaves, no fertile specimen has been discovered. This negative evidence may prove to be as correct as that which led Stur[1355] to exclude Neuropteris, Alethopteris and Odontopteris from the ferns. The only evidence of a positive kind is that furnished by Dr David White in his recent Report on the Palaeozoic Flora of South Brazil. This author describes some small Aphlebia-like leaves under two new generic names Arberia[1356] and Derbyella[1357]. The differences between the two sets of specimens, so far as can be determined from the reproductions of imperfect impressions, are slight, and it is by no means clear that a distinction of generic rank exists. These scale-leaves are on the average about 2 cm. in length; the lamina is oval or rounded and has more or less prominent lobes. In Derbyella there are indications of anastomosing veins. The specimens referred to Arberia minasica are, as White points out, very similar to the fossil described by Feistmantel from Lower Gondwana rocks of India as probably a portion of an inflorescence of Noeggerathiopsis[1358]. Feistmantel’s specimen is represented in [fig. 346]: the curled lobes may have originally borne seeds. In the Brazilian examples the abruptly truncated lobes “bear evidence of separation from reproductive bodies.” An important point is the association of these scale-leaves with Gangamopteris fronds and with gymnospermous seeds of the Samaropsis type. On the leaves assigned to Derbyella aurita circular depressions occur at the base of the lobes which are described as probably due to sporangia.
Dr White’s discovery gives us increased confidence in expressing the view that Gangamopteris bore its reproductive organs on specialised leaves very different from the sterile fronds; it also strengthens the suspicion that the genus is a member of the class of seed-bearing fern-like plants.
Fig. 346. Arberia sp. (= Noeggerathiopsis of Feistmantel). (Nat. size. After Feistmantel.)