A Biogeographical Comparison between Yunnan, Southwest China, and Taiwan, Southeast China, with Implications for the Evolutionary History of the East Asian Flora
Located in southwestern and southeastern China, respectively, Yunnan and Taiwan are of biogeographical significance for the floristic diversity and evolution of the East Asian flora. A total of 13,253 seed plant species in 2140 genera and 225 families are recognized from Yunnan, while 3411 species in 1234 genera and 190 families are recognized from Taiwan. Although the flora of Yunnan is much more diverse than the flora of Taiwan, it is conspicuously similar in floristic composition and biogeographical elements. Yunnan and Taiwan share many of the same species-rich families in their floras. In both areas, families of tropical distribution contribute 52.4% and 50.5% of the total families in Yunnan and Taiwan, respectively, and the genera of tropical distribution contribute 57.3% of the flora in Yunnan and 60.9% of the flora in Taiwan. Yunnan and Taiwan have floristic similarities of 96.3% at the family level and 84.7% at the generic level. These similarities indicate that Yunnan and Taiwan have close floristic affinities. However, the floras of Yunnan and Taiwan have diverged to some extent. Yunnan has eight East Asian families and two Chinese endemic families, of which only two East Asian families are shared with Taiwan. Of the 12 tropical Asian families in Yunnan, 10 are not seen in Taiwan. Compared to Taiwan, Yunnan has 474 genera of tropical Asian distribution, which contribute 22.1% of its total genera, while Taiwan has 165 genera of tropical Asian distribution, contributing only 13.4% of its total genera. Furthermore, the patterns of geographical elements indicate that genera with transcontinental distributions, such as pantropic, Old World tropic, north temperate, or East Asia and North America disjunctions, are more likely to be shared by Yunnan and Taiwan, while those genera with distributions of tropical Asia, Old World temperate, temperate Asia, Mediterranean and western to central Asia, East Asia, and Chinese endemic are more often represented only in Yunnan. The flora of Yunnan might be derived from a Tertiary subtropical East Asian flora and has been diversified in its biogeographical elements following tectonic events since the Late Tertiary: northwestern Yunnan has evolved a temperate-featured flora with the uplift of the Himalayas, and southern Yunnan has evolved a tropical Asian flora with extrusion of the Indochina block. The flora of Taiwan could mainly derive from the East Asian flora with uplifting to an island after the Late Tertiary, and could have a relatively unsophisticated evolutionary history compared to Yunnan.