The Tanaka-Kaiyong Line-An Important Floristic Line for the Study of the Flora of East Asia

Abstract

The is a line separating two Aoristic subkingdoms of East Asia, the Sino-Japanese to the east and the Sino-Himalayan to the west. It lies in the provinces of Sichuan and Yunnan in China. It is comprised of the Tanaka Line of Citrus Distribution in Yunnan province and the Kaiyong Line of Orchid Distribution in Sichuan province, which nearly connect at the border of NW Yunnan and SW Sichuan. Alter a sun ey of the distribution patterns of some genera, we are sure that it exists. The Tanaka-Kaiyong Line is significant not only for the subdivision of the East Asia Kingdom and the Aoristic regionalization of China, but also for the separation of some critical species and the study of vicariance. Moreover, three important Aoristic regions, the Hengduan Mountain region, Central China region, and Dian-Qian-Gui region, which are noted for species abundance, endemism, and high speciation, are situated near this Line. Compared with Sino-Himalayan genera, the Sino-Japanese are more completely separated by the Tanaka-Kaiyong Line, possibly due to their different florogenetic backgrounds and different times of origin. Additionally it seems that the centers of biodiversity (or abundance centers) of Chinese endemic genera on each side of the Tanaka-Kaiyong Line are different. The centers on the west side of the Line are mainly neoendemic, but those on the east are mainly paleoendemic. This difference may be caused by geological-geomorphological patterns and the large-scale climatic conditions in China. The formation of Hengduan Mountain and Yunnan Plateau, which was induced by the uplifting of the Himalayas, greatly affected the Aoristic nature of western Last Asia and, therefore, the floristic distributions that led us to define the Tanaka-Kaiyong Line have probably arisen since that time.