Biogeographical and ecological studies on the vegetation and flora of tropical southwestern China revealed that it is comprised of Indo-Malaysian flora and has true evergreen rain forest with the same forest profile and physiognomic characteristics as equatorial lowland rain forests. The tropical flora in southern Yunnan differs from that of southeastern Yunnan, although the two regions have a similar climate and the same tropical rain forest at lowlands as those of southeastern Asia.
Prof. ZHU Hua of Xishuangbanna Tropical Botanical Garden (XTBG) conducted a study to discuss the biogeographical divergence between tropical southern Yunnan (21°09′ and 22°36′ N, 99°58′ and 101°50′ E)and tropical southeastern Yunnan (22°26′ and 23°26′N, 104°27′ and 108°48′E). He analyzed the floristic and geographical attributes of the two floras, quantified the distribution of seed plants at the generic level in each region, and compared both floristic and geographical elements to assess the floristic divergence between the two regions.
Geographical elements at the generic level reveal that the floras of southern and tropical southeastern Yunnan are dominated by tropical elements, of which, the tropical Asian elements make up the highest proportion. Both floras were therefore categorized as the tropical Asian flora in the floristic regionalization of the world, i.e. they belong to the Malaysia subkingdom of the Paleotropical kingdom. However, the families with temperate distributions have conspicuously more species in tropical southeastern Yunnan, and 14 mainly east Asian families are found in tropical southeastern Yunnan, but not in southern Yunnan.
The flora of tropical southeastern Yunnan is more closely related to Eastern Asian flora, while the flora of southern Yunnan is more closely related to Indo-Malaysian flora. The divergence of the flora is well supported by the geological history of the region; the flora of tropical southeastern Yunnan was mainly derived from the South China Geoblock, while the southern Yunnan flora derived from the Shan-Thai Geoblock.
The study entitled “The Floras of Southern and Tropical Southeastern Yunnan Have Been Shaped by Divergent Geological Histories” has been published in PLoS ONE, 8(5): e64213, doi:10.1371/journal.pone.0064213