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Kunia venusta gen. et sp. nov. is reported from the late Middle Devonian (Givetian) Haikou Formation near Kunming City, Yunnan Province, China. This plant has three orders of naked axes that divide pseudomonopodially. The second- and third-order axes occur in a helix. Fertile appendages are distantly spaced and helically inserted to the third-order axis; they comprise equally dichotomous branches terminated by two clusters of paired and fusiform sporangia. Sterile appendages are dichotomous and distally recurved. A comparison is made with the basal euphyllophytes including the trimerophytes, cladoxylopsids, zygopterids, stauropterids, and some relevant genera of uncertain affinity. The new plant resembles them in dichotomous appendages with terminal elongated sporangia, but differs mainly in the three orders of pseudomonopodial axes bearing helical laterals. It is thus placed in the Euphyllophytina as incertae sedis. It is suggested that an evolutionary divergence in the branching pattern and appendage morphology might have occurred in the Middle Devonian euphyllophytes, that is, maintaining three dimensions versus yielding more or less planation. [ABSTRACT FROM AUTHOR]

We describe the tracheid ultrastructure of Hsüa deflexa from the Lower Devonian (upper Pragian-lower Emsian) Xujiachong Formation, Qujing District, Yunnan Province, China. Scanning electron microscopy study of fusainized and permineralized tracheids shows that they are of G-type, bearing many irregularly distributed perforations. The cell wall consists of a decay-resistant inner part lining the cell lumen and a nonresistant outer part. The resistant inner part, i.e., the assumed heavily lignified secondary wall, is continuous over the poorly lignified outer part that comprises the primary wall and discontinuous secondary wall. It forms the annular thickening over the discontinuous secondary wall. The heavily lignified secondary wall may be divided into three layers. Minute perforations occur on the entire heavily lignified secondary wall, i.e., between and on the thickenings. Concerning the distribution, density, and diameter of perforations, G-type tracheids of H. deflexa share some characters of S-type tracheids. Based on observations of casts, cell wall perforation is cylindrical, with a smooth enclosing wall and two slightly enlarged ends. Lumen casts of tracheids have been formed in several stages. The tracheid ultrastructure of H. deflexa supports the theory of two depositional processes for the secondary cell wall. It indicates that at the genus level of Devonian plants, G-type tracheids differentiate in wall perforation characters; the chemical diversification of the secondary cell wall might have occurred by the Early Devonian. Moreover, this work adds to our knowledge about the evolution of tracheids and early land vascular plants. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: A new plant, Dibracophyton acrovatum gen. et sp. nov., is described from the Lower Devonian (Pragian) Posongchong Formation of Wenshan District, southeastern Yunnan, China. The plant has creeping axes from which arise vegetative and fertile axes. The vegetative axes helically bear lateral dichotomous appendages with curved or round tips. The fertile axes possess terminal strobili with numerous fertile units arranged in irregular helices. Each fertile unit consists of a stalked long-elliptical sporangium, with dehiscence into two equal valves, and two discrete long-ovate bracts covering sporangium from above–below directions. A new genus and species is thus established based on these characters and is temporarily regarded as incertae sedis of Tracheophyta, although it perhaps closes to the barinophytes in affinity. Detailed comparisons with other plants having a similar architecture, i.e., sporangia closely associated with modified vegetative structures, are made. The discovery of D. acrovatum further enriches the composition of the Posongchong flora and demonstrates great morphological disparity of the Early Devonian vascular plants. [Copyright &y& Elsevier]

Abstract: A new species of early vascular plant, Adoketophyton parvulum sp. nov., is described from the Lower Devonian (Pragian) Posongchong Formation of Yunnan, China. The plant is composed of main axes, lateral vegetative branches and isotomous or anisotomous fertile axes. The vegetative axes branch isotomously or pseudomonopodially in three dimensions, with some laterals ending in terminal circinately coiled tips. K-shaped branching and tubercles are preserved. Terminal strobili consist of four vertical rows of fertile units, arranged in opposite and decussate pairs. Each fertile unit comprises a fan-shaped sporophyll and a sporangium attached adaxially by a short stalk at the base of the sporophyll. The strobili and fertile units (sporophylls and associated sporangia) of this new species are much smaller than those of the type species, Adoketophyton subverticillatum, and the ratio of heights of sporangia to sporophyll laminae in the two species shows a large discrepancy. The affinity and evolution of Adoketophyton are discussed. The various leaf-like appendages in plants reported from the Early Devonian of South China are considered a phenomenon of convergent evolution. [Copyright &y& Elsevier]