A new Ephedra macrofossil from the Early Cretaceous Yixian Formation, Liaoning Province, China and its evolutionary significance

Abstract

Despite the significance of Gnetales in understanding the origin and evolution of seed plants, the morphological diversity of ancestral forms within this group remains unclear, and the evolutionary processes affecting their vegetative and reproductive structures lack robust evidence. In this study, we describe a new ephedroid macrofossil from the Lower Cretaceous Yixian Formation in western Liaoning, China. This species is characterized by decussate phyllotaxy, internodes with fine longitudinal striations, swollen nodes, and female cones featuring paired bracts and one to two seeds. While these characteristics resembled extant Ephedra, there are notable morphological differences, including oppositely branched stems of equal length and a seed envelope with transversely aligned epidermal cells on its surface. Consequently, we designate this new macrofossil reproductive shoot as a new species, Ephedra transversa sp. nov.. The findings of this study support the reduction and sterilization hypothesis and enhance our understanding of the evolutionary processes within Gnetales.