An advanced species of the fern Botryopteris Renault from the Permian of southwestern China

Abstract

We describe a new species of the Paleozoic fern genus Botryopteris in volcanic tuffs from the Lopingian (upper Permian) aged Junlian Formation in SW China's Sichuan Province. The species has a large stem and stele compared to those of some other species of the genus. Xylem strands of the leaf trace and rachis are “ω”-shaped in cross section and comprise two long lateral arms and a single, shorter median arm. Parenchyma is distributed among the stem metaxylem tracheids and is more common in the central region of the stele that comprises a parenchymatized protostele. Several mesarch protoxylem strands, decurrent from leaf traces, are visible in each cross section of the protostele. Root traces originate from the lateral side of the leaf trace within the stem cortex. The stem surface is covered by thick, multiseriate, multicellular trichomes. Botryopteris multifolia sp. nov. represents the stratigraphically youngest known species of the genus and has a combination of derived evolutionary characteristics including its large stem size, parenchymatized protostele, elaborate trichome structure, roots originating from leaf traces, and the construction of xylem strand of the leaf trace and rachis with distinctive pinna trace formation and emission. It is more similar in leaf anatomy to the Gondwanan species B. nollii from the Permian of Brazil and less like late Pennsylvanian botryopterids from Euramerica. Finally, we consider the evolutionary implications of features shared between Permian members of the botryopterids and catenalean-type plants including members of the Osmundales stem group family Guaireaceae (Shuichengella, Zhongmingella, Tiania) and the enigmatic early ferns Rastropteris and Catenopteris.