The first megafossil of Cibotium within its modern distribution

The ‘man fern’ (Cibotium, Cibotiaceae), a typical tree fern of tropical and subtropical climates, is today mainly distributed in the Hawaiian Islands, Mesoamerica, and tropical and subtropical regions of East and Southeast Asia. Reliable fossil records of this genus are rare. Only two cases of stem fossils have been reported from the Upper Cretaceous of Iwate-Ken, Japan and the upper Eocene of Oregon, USA. In this paper, ultimate fertile pinna fossils of Cibotium are described from the Miocene Erzitang Formation of Guiping Basin, Guangxi Zhuang Autonomous Region, South China, which also preserve in situ spores and cuticles. As the first global discovery of Cibotium pinna fossils preserving both in situ spores and cuticles, this find enriches the organ types of Cibotium fossils. This is also the first discovery of Cibotium fossils within its modern distribution range, indicating that Cibotium had migrated southwards into its modern distribution by at least the Miocene. Based on the modern habitat of Cibotium, we infer that the Guiping Basin was under a warm and humid tropical/subtropical climate in the Miocene.