Zosterophyllum Penhallow around the Silurian‐Devonian Boundary of Northeastern Yunnan, China
Two new species of Zosterophyllum Penhallow (Zosterophyllum qujingense sp. nov. and Zosterophyllum xishanense sp. nov.), respectively from the Yulongsi Formation (Late Silurian, Přídolí) and Xiaxishancun Formation (Early Devonian, Lochkovian) of Qujing, Yunnan, China, are described. Both are small and naked plants with spikes of radially arranged sporangia. Zosterophyllum qujingense is the earliest recorded plant of Zosterophyllum in South China. It has basal K‐ or H‐shaped branching and erect dichotomous axes. Terminal spikes consist of lateral and stalked sporangia of wedge or somewhat elliptical shape. Arising from the rhizome, fertile axes of Z. xishanense bear laterally stalked and more or less round sporangia. Configuration of the rhizomatous part and K‐ or H‐shaped branching of Z. xishanense are discussed. Comparison with other zosterophylls indicates that the Late Silurian–Early Devonian flora of the paleoequatorial zone (i.e., Bathurst Island and Qujing, Yunnan) may be characterized by a diversity of zosterophylls, probably differing from coeval floras of other regions dominated by rhyniophytoids. With regard to paleophytogeography, we suggest that the zosterophylls bearing radially arranged sporangia (including subgenus Zosterophyllum) were prevalent in South China (northeastern Gondwana phytogeographic unit) and that those with one or two rows of sporangia (subgenus Platyzosterophyllum) were common on the Laurussian paleocontinent.