A new species of Estinnophyton from the Lower Devonian Posongchong Formation, Yunnan, China; its phylogenetic and palaeophytogeographical significance

Abstract

A new species of early vascular land plant, Estinnophyton yunnanense, is described from the Lower Devonian (upper Pragian) Posongchong Formation at Zhichang village, Gumu Town, Wenshan District, Yunnan Province, China. This plant possesses aerial stems with isotomous branching. The leaves are slender, once- or twice-bifurcated, and arranged in low spirals or pseudowhorls. Fertile leaves are morphologically identical to the vegetative ones, clustered on the axis, forming a loose strobilus-like structure. There are three to six fertile leaves in each gyre. Two ovoid-elongate sporangia are singly attached to the adaxial surface each subtended by a recurved stalk, either at the base of each segment in a once-bifurcate fertile leaf or below the points of successive divisions in a twice-bifurcate fertile leaf. Estinnophyton yunnanense differs from two other species described previously from Europe, E. gracile and E. wahnbachense, mainly in possessing two single stalked sporangia on each fertile leaf rather than two pairs of sporangia, as well as in the dimensions of its leaves. In view of the complex taxonomy and nomenclature surrounding the type material of Estinnophyton, we considered possible emendation of the generic diagnosis based on the new Chinese material. Following comparison with typical members of the Protolepidodendrales and other taxa, Estinnophyton is considered to have had a closer affinity with primitive sphenopsids than the protolepidodendralean lycopsids. A comparison between Chinese and European floras containing Estinnophyton indicates that South China and Western Europe had floristic elements in common although they were in different phytogeographical units during the Early Devonian epoch.