Abstract
Morphology and nomenclature are essential issues of botany, in which both extant and fossil plant taxa follow the same nomenclature code. Devonian (419.2-358.9 Ma) herbaceous lycopsid Barsassia, one of the earliest coal-forming plants in geological history, possesses a characteristic, easily recognized, step-like stem and has been thought to be an index fossil for dating and correlating the Middle Devonian strata, especially those in the paleoblocks of Siberia, Kazakhstan, Xinjiang, and North China. Here, we systematically study the Devonian lycopsid Barsassia in terms of its morphology and nomenclature, based on the new materials from the Middle Devonian Hujiersite Formation of West Junggar, Xinjiang, China, and the International Code of Nomenclature for algae, fungi, and plants (Shenzhen Code). Barsassia ornata is determined as the type species of the genus, and a neotype is designated for that name. Barsassia ornata consists of fan- or rectangular-shaped leaves with awl-shaped or finger-like distal tips. Its leaves are pseudo-whorls and imbricately arranged on the stem surface forming distinct step-like structure.