Guangnania cuneata gen. et sp. nov. from the Lower Devonian of Yunnan Province, China

Abstract

Guangnania cuneata gen. et sp. nov. has been collected from the Lower Devonian (Pragian) Posongchong Formation of southeast Yunnan and the (Pragian-early Emsian) Xujiachong Formation of east Yunnan, China. The plant possesses dichotomous branches. The fertile region consists of lateral sporangia attached helically. Each sporangium is elongate cuneate and long-stalked. It dehisces into two unequal valves, a large abaxial valve and a small adaxial one, which in transverse section are curved towards the axis. The dehiscence line is bordered by the thickening along the entire sporangial valve margin. The elongate, curved shape and unequal valves of the long-stalked lateral sporangia make this plant a new genus. We suggest that morphological variation in the zosterophylls includes the sporangial shape, i.e. reniform, rounded/globose to vertically elongate. On this basis, the lateral sporangial position and the sporangial rim bordering the dehiscence line, Guangnania may be provisionally allied to the zosterophylls, although stelar anatomy is unknown. The common occurrence of Zosterophyllum australianum Lang et Cookson 1930, Huia Geng 1985 and this new plant during the Early Devonian (Pragian) suggests that the Posongchong flora and mid-lower assemblage of the Xujiachong flora show some similarities in composition and coeval. The disparity in these two floras is probably due to different environments in which plants lived and were preserved.