A new zosterophyll from the Lower Denovian (Siegenian) of Yunnan, China

Abstract

A new genus and species, Discalis longistipa, is described from the Posongchong Formation (Siegenian), Wenshan district of Yunnan, China. The plant has creeping axes with numerous K- or H-shaped branches. Aerial branches are either trailing, or upwardly growing, dividing sterile axes with circinately coiled tips and fertile axes with laterally born, disc-like round sporangia. The rather large sporangia, about 3.7 mm in diameter with rather long stalks (up to 5 mm), are sparsely or somewhat compactly scattered along the fertile axes, sometimes spirally, forming loose spikes. It is noteworthy that variable spines with expanded oblate apices, which possibly relate to glands, occur irregularly on the plant, along the stalks, and on the sporangium walls. Discalis longistipa is superficially similar to the genus Sawdonia, but it differs from the latter in the arrangement of its sporangia, the long sporangial stalks and the mode of branching. The discovery of this new plant contributes to our knowledge of early vascular plants. It is of interest to recognize the diversity of them and to speculate about the origins of the microphyll and sporophyll.