A new basal euphyllophyte, Pauthecophyton gen. nov., from the Lower Devonian (Pragian) of Yunnan, China

Pauthecophyton gracile gen. et sp. nov. is described from the Lower Devonian (Pragian) Posongchong Formation near Zhichang Village of Wenshan District, southeastern Yunnan, China. This plant consists of pseudomonopodially and dichotomously branched main axes and lateral branches. Some laterals are pseudomonopodially divided producing three to four times dichotomously branched systems terminating in sporangia; other branches are isotomously divided six to eight times terminating in sporangia. Fusiform sporangia are grouped as fertile units; each unit, generally with two, three or four sporangia, is subtended by a branch which generally divides once or twice. Sporangia lacking twisting have a longitudinal dehiscence and contain similarly sized spores with laevigate and folded exine. Pauthecophyton probably occupies a basal position within the euphyllophytes, as one of the earliest divergent clades. It is more similar to the genus Psilophyton Dawson than to others in branching, as well as sporangial shape, terminal position and longitudinal dehiscence; these similarities, more likely to be plesiomorphic characters of the euphyllophytes, indicate that they both belong to the “trimerophyte grade”. The character of twisted sporangia in trimerophytes and the phytogeographic isolation of euphyllophytes in South China are discussed.

► New basal euphyllophyte plant similar to Psilophyton from Lower Devonian of China ► Plant with pseudomonopodially and dichotomously branched axes ► Fertile unit generally with two, three or four sporangia ► As a plant of traditional “trimerophyte grade”, its sporangia do not twist.