The geographical distribution of Aristolochia kaempferi and A. shimadae (Aristolochiaceae) from the midwestern Kinki region to the eastern Setouchi region in Japan was investigated through field surveys and transplanted materials. In this region, A. kaempferi and A. shimadae are not common and flowering individuals are rare, while the latter is usually observed flowering around the area of Mt. Rokko, Hyogo Prefecture. Based on the identification by flower morphology, the distributional boundary between A. kaempferi and A. shimadae was found to be located in the southwestern part of Hyogo Prefecture. Additionally, the examination of chloroplast DNA showed that the geographical boundary between the previously recognized two lineages was located west of the distributional boundary between the two species.
