Liknopetalon: a review of a rare Gondwanan, Permian pteridophyte

Abstract

Liknopetalon is an unusual fern-like taxon with fan-shaped pinnae that bear ovate sporangial bodies in a single series along the distal margin. Previously, Liknopetalon has been described from two Permian localities in South Africa, and a single pinna has been identified from the Perth Basin in Australia. The original material of the type species, Liknopetalon enigmata Smithies, lacks critical morphological characters and the species’ taxonomic affiliations have remained obscure. A re-evaluation of existing collections and additional information provided by material obtained from a third South African locality necessitated emendation of the generic diagnosis of Liknopetalon, and erection of an additional species, Liknopetalon gracilis Adendorff sp. nov. Detailed drawings and photographs of several important specimens are presented and these have contributed to the reconstruction of both species. Newly clarified features include the opposite arrangement of the pinnae on the rachis, the division of the distal margin of the lamina into a series of contiguous lobes that each bear a single sporangial body, and the absence of a longitudinal, medial cleft in the pinna. Without anatomical data, the nature of the marginal bodies could not be unequivocally elucidated, but based on gross morphology, they appear to represent synangia or particularly large sporangia. The new South African specimens extend the stratigraphic range of the plant from the Lower Permian into the Middle Permian.