A small, heterophyllous vine climbing on Psaronius and Cordaites trees in the earliest Permian forests of North China

Premise of research. Climbing plants are important components of modern-day tropical forests and primarily comprise angiosperms, but in Paleozoic tropical forests, pteridosperms were the dominant climbers. Climbing pteridosperms are well known from the Paleozoic floras of Euramerica, while much less is known about climbing pteridosperms from other phytogeographic regions. We document from the earliest Permian Taiyuan Formation of Cathaysia a new genus and species of a small vine preserved in situ and in 3D in a volcanic tuff bed from the Wuda locality. We consider the affinity and ecology of the new plant and evaluate its abundance and distribution in the Wuda forest community.

Methodology. Macrofossils were prepared by dégagement, and sharpened needles were used to expose the plant from the overlying sediment. Anatomy was revealed by petrological thin sections. Key features of the plant were observed under scanning electron microscopy.

Pivotal results. Only the aerial organs of the plant are known, and they comprise stems up to 4.5 mm in diameter that bear hooked prickles and fronds. Branching is irregular, probably axillary, with buds situated in axils of the stem and fronds. Stems are eustelic with well-developed secondary xylem. Lanceolate and distinctly asymmetric bipinnate fronds arise from the stem in nodes. Fronds show considerable variation in both size and shape, and pinnules are strongly heterophyllous. Large pinnules have relatively long conical pinnule lobes terminated by pads that are adapted for climbing, which we consider to be pinnule climbing adaptations. Epidermal cells on pinnules have large paracytic stomatal apparatuses. Fertile pinnules with well-developed pinnule laminae appear to have borne reproductive organs above lateral veins and between the midvein and the pinnule margin on the lower (abaxial) pinnule surface. Fertile structures are incompletely preserved and appear to represent pollen organs; seeds are unknown.

Conclusions. Although its fertile organs are unknown, characters of the new plant are most similar to those of the pteridosperm family Callistophytales and in particular Callistophyton, but it is distinct from existing genera, leading to the erection of Wudaeophyton wangii gen. et sp. nov. Wudaeophyton wangii is reconstructed as a vine climbing on Psaronius marattialean fern associations in the bottom of the tuff bed and on Cordaites gymnosperm associations at the top. We interpret W. wangii to most likely be a member of the Callistophytales, leading us to consider the persistence and evolutionary diversification of Callistophytales in the Cathaysian floras after their regional extirpation in Euramerica, which broadly coincided with the onset of the Permian, and their eventual extinction in the Lopingian (upper Permian) before the end-Permian mass extinction event.