A new marattialean fern, Pectinangium xuanweiense sp. nov., from the Lopingian of Southwest China

A new species of adpressed marattialean fern with vegetative and fertile pinnules, Pectinangium xuanweiense sp. nov., is described from the Lopingian (upper Permian) in eastern Yunnan and western Guizhou provinces, Southwest China. The fronds of this new species are at least bipinnate, with linear to lanceolate ultimate pinnae. The pinnules are alternately arranged and pecopterid-type with pinnate venation. Fertile pinnules show recurved margins and abaxially bear a row of synangia on each side of the midvein. Synangia are 0.7 mm long and 0.4 mm wide on average, arranged in a density of approximately 16 per centimeter. Each synangium consists of four sporangia that are completely fused in well-regulated rectangular/ovoid shapes in the distal view. Sporangia are exannulate, 370 μm long and 200 μm wide on average. The sporangial walls are composed of at least three layers of elongated rectangular to polygonal cells. In situ spores are circular to oval, 25-(30)-35 μm in diameter, with trilete marks and microverrucate sculptures. Ultrastructural investigations indicated that the exine encompasses a perine, sexine, and nexine. In situ spores correspond to Verrucosisporites if found as sporae dispersae, and thus indicate that P. xuanweiense sp. nov. belongs to the Acitheca miltonii Group (palynological grouping) of Paleozoic marattialeans. Our study provides insight into the diversity of late Permian marattialeans in the tropics of the eastern Paleo-Tethys ocean.