Diversity in affinities of plants with lateral sporangia from the Lower Devonian of Sichuan Province, China

Five plant species, all with lateral sporangia aggregated into strobili terminating smooth stems, have been circumscribed from the Lower Devonian Pingyipu Group exposed in Jiangyou County, Sichuan, China. Four have involved reinvestigation of fossils described more than twenty years ago plus, in some instances, observations on more recently collected fossils, whilst the fifth, Adoketophyton pingyipuensis sp. nov., unusual in that the strobilus contains bracts, is based on new material. The fossils are preserved as coalified compressions and impressions and lack anatomy. Zosterophyllum ovatum was originally called Zosterophyllum myretonianum, but mainly differs from the type species in sporangial shape. The plant first named Zosterophyllum sichuanensis has been placed in a new genus Ornicephalum, because it possesses bivalved sporangia with markedly unequal valves. Two species of Amplectosporangium, whose terminal fertile complexes are unique because they comprise collections of dichotomously branching axes bearing rows of sessile or almost sessile sporangia, are distinguished by the amount of branching in the fertile complex and on sporangial shape. The one with simpler branching was originally placed in the North American genus Oricilla. The classification of the zosterophylls, relationships within the lycophytes and, in this study, particularly the affinities of Adoketophyton, here considered a barinophyte, require revision. Considering geographical relations, at species level all taxa are restricted to the locality. At generic level, Zosterophyllum is cosmopolitan, Adoketophyton is also recorded in Yunnan, whilst Amplectosporangium and Ornicephalum are restricted to Sichuan, providing further evidence for the preponderance of endemicity in Chinese Lower Devonian vegetation whilst reinforcing differences between the assemblages in the two Chinese provinces. The reasons for this remain conjectural.