Fossil pods of tropical tree Peltophorum (Caesalpinioideae, Fabaceae) from southwestern China

Abstract

Peltophorum (Fabaceae, Caesalpinioideae) is a pantropically distributed deciduous tree, whose biogeographic origin and development remain unclear due to limited fossil records. As the only genus with Asian distribution in its tribe, Peltophorum's fossil records from Asia are crucial for understanding its biogeographic history. In this study, a new species, Peltophorum xingjianii Y.S. Zhao, T.X. Wang et J. Huang sp. nov. is established based on well-preserved pods from the lower Miocene Sanhaogou Formation of Jinggu Basin, Yunnan, southwestern China. The fossil pods exhibit a unique morphological combination, including oblong shape, distinct and uniform V-shape valve venation, and rhombic seed chambers. The nearest living relative is P. pterocarpum, a species currently distributed from Southeast Asia to northern Oceania. This discovery represents the oldest known Peltophorum fossil record, indicating the genus's presence in low-latitude East Asia since at least the early Miocene. This finding, along with other fossil plants from the same basin, points to a tropical paleoenvironment in the early Miocene of Jinggu Basin.