Venation pattern in the sphenophyll Trizygia speciosa Royle from the Raniganj Formation

Abstract

There has been a running controversy about the independent taxonomic status of the genus Trizygia vis-a-vis Sphenophyllum. The basic organisation of the foliage shoot in both the genera is apparently similar, except for the trizygoid leaf whorls in the former. The trizygoid leaf whorls are, however, not unknown in Sphenophyllum. The two genera can not be compared at the level of anatomy of the axes or the organisation of the fertile shoot as this information is not available for Trizygia. The venation pattern in leaves of Trizygia has been analysed in detail with a view to compare it with that of Sphenophyllum, when that information is forthcoming. The parameters chosen for analysis include length, width and area-index of leaves and number of dichotomies, ultimates and dichotomy levels.