The Chinese tropical region has generally been recognized to be the area on the northern edge of tropical Asia, and includes southeastern Xizang (Tibet), southern Yunnan, southwestern Guangxi, southern Taiwan, and Hainan Island. Based on present floristic records and data from these tropical areas, 12,844 species of seed plants including 2,181 genera and 227 families, are recognized. The families that are distributed mainly in tropical areas but extended to the temperate zone contribute to the majority of the flora of tropical China, and genera with tropical distributions make up the most of the total flora, which indicate that the flora of tropical areas in China is marginally tropical in nature. The genera with the tropical Asian distribution contributed to the highest portion among the various distribution types, which implies tropical Asian or Indo-Malaysia affinity of the tropical flora of China. The tropical flora of China has conspicuous variations in floristic composition and geographical elements from region to region due to different geological history and ecological environments, although the floristic similarities at the family and generic levels are more than 90% and 64%, respectively but lower than 50% at the specific level, among the compared regional floras from southwestern China and southeastern China. We found that there are more similar dominant families and genera, and also higher similarities between families and genera between southeastern Tibet (Xizang) and southeastern Yunnan. The floras of southern and southeastern Yunnan have a higher portion of the tropical Asian elements compared with other tropical floras in China, and although they have the highest similarity at specific level, the dominant families and genera have conspicuous differences between them. The flora of Hainan has the highest ratio of tropical elements, of which the pan-tropical element has the highest portion. Differences in characteristics and evolution in these tropical floras could be influenced mainly by historical events occurring with uplift of Himalayas, such as the southeastward extrusion of the Indochina geoblock, clockwise rotation and southeastward movement of Lanping-Simao geoblock, divergent geological histories between southern and southeastern Yunnan, and southeastward movement of Hainan Island.
Received: 26 February 2016
Published: 06 March 2017