An early Oligocene occurrence of the palaeoendemic genus Dipteronia (Sapindaceae) from Southwest China

Palaeoendemic plants, whose past geographical distribution was much larger than their present distribution ranges, play an important role in reconstructing biogeographical events, and in tracking floristic relationships among continents throughout geological time. Improving knowledge about their geographical histories helps to understand the evolution of biodiversity under palaeoenvironmental changes. Here, we report the first fossil record of Dipteronia from East Asia, namely Dipteronia brownii McClain et Manchester, based on diagnostic winged fruit remains from the Rupelian (c. 32 ± 1 Ma) of the Lühe Basin in southwestern China. The fossil species is characterized by (i) a samaroid mericarp, with an orbicular wing, (ii) a primary vein extending from the attachment scar, and ramifying into secondary and tertiary veins that radiate out from the seed body area and dichotomize toward the mericarp. Dipteronia was widely distributed in the Northern Hemisphere during the Palaeogene and is now endemic to central and southwestern China with two extant species. This new finding significantly expands the historical distribution of Dipteronia into China by the early Oligocene, and its present-day endemism is apparently the result of extirpation from North America and the higher latitudes of Asia associated with Cenozoic climatic changes.