Dominant gymnosperms of the Glossopteris flora

Abstract

The paper presents, new ideas about the Lower Gondwana forests which the author believes were dominated by deciduous gymnospermous trees of Glossopteris and its allied genera. It is suggested that the larger trees of glossopterids may have been 30 to 40 m or more in height and below them grew shorter trees and shrubs of Glossopteris and its allies. The large size of glossopterid trees is suggested by that of tree trunks assigned to Dadoxylon sp. from the Raniganj Stage where Glossopteris is the commonest fossil and the genus Noeggerathiopsis, to which they had been assigned earlier, is a rarity. Such trees could have been supported by horizontally spreading axes or roots at the base of the trunks as suggested by fossil axes or roots around missing trunks reported from the bed of Vaal River in South Africa which too had been assigned to Noeggerathiopsis.

The deciduous glossopterid trees are compared with those of modern Ginkgo biloba. It is suggested that the gradate series of glossopterid leaves with Glossopteris having a midrib and anastomosing laterals at one end of the series followed by leaves of Gangamopteris with anastomosing laterals and no midrib. Rhabdotaenia with a midrib and dichotomising non-anastomosing laterals. Palaeovittaria with a midrib in the lower half and non-anastomosing spreading laterals, in the distal part. Rubidgea without a midrib and spreading arched laterals and Noeggerathiopsis with dichotomising spreading straight veins at the other end may form a series of leaves which may be related to each other. It is considered that Noeggerathiopsis may not be a cordaite.

The morphological nature of the fertiligers of glossopterids are discussed and compared with certain abnormal peduncles of Ginkgo biloba and it is pointed out that 10 per cent of the leaves of this genus show anastomoses and this genus may be allied to Glossopteris. In addition, indubitable evidence in support of the in situ or autochthonous mode of formation of Lower Gondwana coal is also discussed.