Xihuphyllum, a novel sphenopsid plant with large laminate leaves from the Upper Devonian of South China

The sphenopsids first appeared in the Late Devonian, becoming diverse in the Carboniferous and Permian, but are represented now by the single genus Equisetum. In this article, morphologically preserved material of the novel sphenopsid plant, Xihuphyllum megalofolium (Wu) Chen emend. Huang et al., is described from the Upper Devonian Wutong Formation of Zhejiang Province, China, providing new data on the early evolutionary history of this group. This plant is characterized by a hierarchical branching pattern, with robust nodose stems up to 42.5 mm wide and two orders of lateral branches. Morphometric studies show that the internode width of stems and first order branches are correlated with the internode length. Leaves, cuneate, broadly cuneate, or spatulate in shape and highly variable in size, are arranged in whorls at the nodes of stems and branches. The leaves of Xihuphyllum reach over 80 mm in length and >3000 mm(2) in area, an unusually large size for Paleozoic sphenopsids. Xihuphyllum is reconstructed as having a stature 2-3 m in height, and represents an early, large-bodied member within the extinct Sphenophyllales. The occurrence of Xihuphyllum and contemporaneous members of the same group, including Eviostachya, Hamatophyton, Rotafolia and Sphenophyllum, indicates early diversification of sphenopsids in South China. (C) 2016 Elsevier B.V. All rights reserved.National Natural Science Foundation of China [41672007, 41272018]; Yunnan Key Laboratory for Palaeobiology, Yunnan University [2015DG007-KF04]SCI(E)ARTICLE7-2046