Phylogeography of eastern Asian plants associated with vicariance in the northwestern Yunnan Province, China.

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The flora of the Sino-Japanese plant region of Eastern Asia is distinctively rich compared with other floristic regions in the world ; however, knowledge of its floristic evolution is fairly limited. Our aim was to provide insight into floristic evolution in eastern Asia on the basis of a molecular phylogeny and genomic differentiation (chromosome information) of several taxa. Phylogenetic analyses' of three DNA regions confirmed that Ainsliaea (Compositae) is composed of three major clades that correspond to species distributions. Evolution of the three lineages was estimated to have occurred around 1.1 MYA in the early Pleistocene of the Quaternary. Our results suggest that Ainsliaea species evolved allopatrically and that the descendants were isolated in the eastern (between SE China and Japan, through Taiwan and the Ryukyu Islands) and western (Yunnan Province and its surrounding areas, including the Himalayas, the temperate region of Southeast Asia, and Sichuan Province) sides of the Sino-Japanese region. From the phylogeny of Ainsliaea species, two environmentally heterogeneous regions within the Sino-Japanese region have independently maintained rich and original floras due to their diverse climates and topographies. Moreover, intraspecific polyploidy and cytogeography were examined for samples of Houttuynia cordata from eastern Asia, ranging from Nepal to Japan through China, northern Thailand, and Taiwan. Five chromosome numbers (2n=72, 80, 96, 112, and 128) were detected, four of which were first recorded here. These chromosome numbers suggest that the basic chromosome number of Houttuynia is x=8. The observed cytotypes were evaluated as 2n=72, 80, 96, 112, and 128, and represent 9x, 10x, 12x, 14x, and 16x, respectively. The continental part of east Asia harbors intraspecific polyploidy ranging from 9x to 16x, and only one cytotype, 12x (2n=96), was found from the eastern edge of the Asian continent, between Taiwan and Japan.