Convergent evolution in the late Permian megaphyllous leaves of the Noeggerathiales progymnosperm Paratingia and the cycad Plagiozamites

Background and Aims The late Permian Xuanwei Formation represents the last refuge Paleozoic fern-dominated Cathaysian (Gigantopteris) flora before its demise in the Permian-Triassic mass extinction. It contains two Noeggerathiales progymnosperm fertile shoots, but unequivocal Noeggerathiales leaves have not been identified. Co-occurring once-pinnate megaphyllous leaves of Plagiozamites oblongifolius, previously interpreted as cycad gymnosperms from morphology and epidermal characters, have also been considered as possible Noeggerathiales fronds based on their distinctive Ω-shaped rachis bundles and four rows of pinnules comprising two rows of large pinnules and two rows of small pinnules. We investigate newly collected P. oblongifolius leaves from the Xuanwei Formation to determine their affinity, accurately characterise species composition, elucidate features to distinguish the leaves of Noeggerathiales and cycads, and consider convergent evolution in these two systematically diverse plant orders.

Methods We examined the morphology and anatomy of Plagiozamites oblongifolius leaves using the acetate peel technique, and transmitted light and scanning electron microscopy.

Key Results The leaves have two rows of large pinnules, two rows of small pinnules, and epidermal characters consistent with Noeggerathiales. From these we identify three new species of the Noeggerathiales genus Paratingia, extending their stratigraphic range to the late Permian. Paratingia leaves are distinct from Plagiozamites cycad leaves, of which at least two species co-occur in the Xuanwei Formation, which have two rows of pinnules and different epidermal characters.

Conclusions Results emphasise parallel evolution in leaf form and anatomy among Noeggerathiales progymnosperms and cycads, which despite superficial resemblance, are distinguished through gross morphology, rachis anatomy, and epidermal characters. Our findings highlight complexities in accurately identifying fossil species from incomplete data and help clarify species richness and extinction magnitude in Cathaysia through the Paleozoic–Mesozoic transition.