Pod fossils of Albizia (Fabaceae: Caesalpinioideae) from the late Miocene of northern Vietnam and their phytogeographic history

The genus Albizia is one of the largest genera in the Fabaceae (the legume family). It is a pantropical genus of eco-logically, economically, and chemically important trees, shrubs, and lianas. Fossil records of the genus have been extensively documented from the late Eocene to Pleistocene in Asia. However, no Albizia fossils have been re-ported from the Cenozoic sediments of Southeast Asia. We describe a new species for pod fossils, namely Albizia yenbaiensis H.B. Nguyen, T. Su & J. Huang sp. nov. obtained from the late Miocene sediments of the Yen Bai Basin, northern Vietnam based on morphological comparison with other legumes. Albizia yenbaiensis is characterized by oblong to broadly linear-shaped, wingless pods, a short stipe, long tapered and slightly oblique base, shortly tapered apex, rounded seed chambers, slightly constricted margins between the seeds, and oblique parallel pri-mary veins on the epicarp. Our discovery represents the first fossil record of Albizia in Southeast Asia. It indicates that Albizia had already existed in a tropical broadleaved forest along the Red River valley in northern Vietnam in the late Miocene. Fossil records of Albizia indicate that the genus might originate in the East Asian Monsoon re-gion and increased the species diversity since the Miocene. The current diversity of the genus in America and Africa could be attributed to its adaptation to warm and seasonally dry climates.(c) 2022 Published by Elsevier B.V.