Late Devonian sphenopsid shows evidence of aquatic adaptations.

Abstract

Vascular plants diversified and adapted to various terrestrial environments during the Silurian and Devonian periods and had formed complex forests by the Middle and Late Devonian¹. However, fossil evidence of functional adaptations to aquatic environments remains scarce, from forms with only submerged subterranean parts to fully submerged types. Notably, emergent plants, with partially submerged shoots, provide insights into how different plant parts utilize ecological resources in aquatic habitats. Sphenopsids (Late Devonian to present, e.g., Equisetum) exhibit nodal axes and whorled appendages (branches, leaves, and roots)^2,3. Among them, the Sphenophyllales, with wedge-shaped or dichotomized leaves, occupied Permo-Carboniferous swamp habitats^3,4. The South China Block was located in the equatorial tropics in the Late Devonian and hosted a significant diversity of sphenopsids³. Here, we report Eviostachya cf. hoegii from the Upper Devonian (Guanshan Member, Wutong Formation), in strata underlying the Xinhang lycopsid forest⁵ from the same localities in Anhui Province, China, exhibiting characteristics that suggest some of the earliest functional emergent adaptations.