Origin and evolution of the flora of Yunnan

Yunnan is an extremely biodiverse area in southwestern China. It includes more than half of all Chinese plant species and the main vegetation types of Eurasia. However, the origin and evolution of its intricate biota are less known to science. Based on geological events in Yunnan since the Tertiary, we investigated the possible origin and evolution of Yunnan flora from the view of floristic biogeography. It was revealed that the flora of Yunnan might be derived from tropical-subtropical Tertiary flora of East Asia, with later divergence. The northwestern Yunnan flora likely evolved through rapid speciation from families and genera of cosmopolitan and north temperate distribution with uplift of the Himalayas and climatic oscillations after the late Tertiary, while southern Yunnan flora evolved tropical Asian flora by permeation of tropical Asian elements with southeastward extrusion of the Indochina block, with central Yunnan inheriting more elements of Tertiary flora from East Asia. The phylogenetic relationships (phylogenetic structure and β-diversity patterns) of the flora of northern, central, and southern Yunnan supported the deduction suggested from biogeography. The oblique abundance patterns of Yunnan seed plants corresponded well to the clockwise rotation and southeastward extrusion of the Langping-Simao (Indochina) Geoblock caused by the collision of India with Asia. The divergence of the flora of southern and southeastern Yunnan, in which the former was more closely related to Indo-Malaysian flora and the latter was more closely related to Eastern Asian flora, was well supported by the geological history of these regions; that is, the flora of tropical southeastern Yunnan derived from the South China Geoblock, whereas the southern Yunnan flora derived from the Shan-Thai Geoblock.