The oldest fossil record of Bauhinia s.s. (Fabaceae) from the Tibetan Plateau sheds light on its evolutionary and biogeographic implications

AbstractBauhinia s.s. is a large genus in the family Fabaceae, but its evolutionary and biogeographical history is still unclear due to the scarcity of fossil records compared to the highly diverse modern species in pantropic regions. Here, we report the earliest fossil record of Bauhinia s.s., namely Bauhinia tibetensis Y. Gao et T. Su sp. nov., based on leaves from the latest Paleocene of the southern Tibetan region. Combined with palaeoecological niche simulations and ancestral state reconstruction, the new fossils suggested a Paleocene origin of Bauhinia s.s. in the Afrotropical realm that subsequently dispersed to the Neotropical and Indomalayan realms. Bauhinia tibetensis belongs to the Asian clade of Bauhinia s.s. that reached the southern Tibetan region from the Afrotropical realm via the Kohistan-Ladakh Island Arc in the early Paleocene. This clade spread to south-eastern China during the Oligocene and entered northern India during the Neogene or earlier. The discovery of the oldest Bauhinia s.s. from what is now the southern Tibetan Plateau updates our understanding of the biogeographical history of this genus and demonstrates that the Kohistan-Ladakh Island Arc is an ancient corridor for floristic interchange between Africa and India.Keywords: Bauhinia s.s.biogeographydiversificationPaleoceneleaf fossilpalaeoecological niche simulations AcknowledgementsWe thank the members of the Paleoecology Research Group from Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences (CAS) and colleagues from Kunming Institute of Botany, CAS for fossil collection works. We thank the Institutional Center for Shared Technologies and Facilities of Xishuangbanna Tropical Botanical Garden, CAS for providing imaging equipment and assisting with fossil scans. This work is supported by the National Key Research and Development Program (2022YFF0800800), the Second Tibetan Plateau Scientific Expedition program (2019QZKK0705), the National Natural Science Foundation of China (NSFC) (41988101), the Strategic Priority Research Program of the Chinese Academy of Sciences (CAS) (XDB26000000), the Youth Innovation Promotion Association, CAS (Y2021105), and the Basic Research Project in Yunnan (YNWR-QNBJ-2019-086).Disclosure statementNo potential conflict of interest was reported by the author(s).Supplemental materialSupplemental material for this article can be accessed here: http://dx.doi.org/10.1080/14772019.2023.2244495.Associate Editor: Paul Kenrick