The morphology of Stauropteris burntislandica P. Bertrand and its megasporangium Bensonites fusiformis R. Scott

Abstract

The Lower Carboniferous Stauropteris .burntislandica is described here in detail. The frond of the plant consists of a repeatedly dichotomizing branch system which is traced up to the ultimate tips. The structure of the node and degree of branching in various orders of branches is described. A reconstruction of a part of the frond is made which suggests that the frond may have been supported on an underground stem. Bensonites has now been shown to be the megasporangium of Stauropteris burntislandica which normally carries two well-developed megaspores, a condition which is unknown elsewhere in the plant kingdom. The sporangium containing small spores which was already known now becomes the microsporangium of the plant. It is suggested that heterospory may be found in other species of Stauropteris also. A comparison is then made with the Zygopterideae and the Psilophytales. Finally, the systematic position of Stauropteris is discussed in the light of new evidence.