Abstract
Albizia kalkora (Leguminosae subfam. Mimosoideae) is a deciduous tree distributed in Japan, China, Korea, and other countries from Southeast Asia to India. In Japan, its distribution is restricted to the evergreen broadleaved forest zone in southern Kyushu, whereas it is widely distributed in the deciduous broadleaved forest zone in China. Fossil records of A. kalkora from the Plio-Pleistocene have been limited in Kyushu, although A. miokalkora, a closely related fossil taxon, from the Miocene has been found in China, Korea, and Japan. We describe herein A. kalkora leaflet fossils from the Lower Pleistocene Sayama Formation and Middle Pleistocene Shoudai Formation in central Japan. We compared the leaflets with those of modern species in China with similar morphology and identified them as those of A. kalkora based on their size (2–3 cm long), the medial and base asymmetry, and the presence of 2–3 slender secondary veins diverging at the base. Their association with evergreen broadleaved trees in fossil assemblages indicates that A. kalkora expanded its distribution to central Japan during stages with warm winter temperatures. Its distribution was limited to southern Kyushu during the Late Quaternary in Japan, whereas in China it expanded widely into the deciduous broadleaved forest zone, possibly by adapting to cold winter conditions during glacial stages.
