Hainan Island, a province of southern China, has high mountains in the center and low lands at the periphery. From the late Mesozoic, the Beibu Gulf lithosphere was drawn away, and Hianan moved southeast along Red River fault and revolved clockwise to the present location. Therefore, the continental or “island” origin of Hainan, and the Indo-Malaysian or mainland affinity of its flora, are still debatable. 

Understanding the affinity and evolution of the Hainan flora is important for understanding the plant geography of Hainan Island. Based mainly in the inventory of Hainan plants, Prof. ZHU Hua of Xishuangbanna Tropical Botanical Garden (XTBG) made a revision of the native plant species by checking, synonymizing, and adding species from their database. He aimed to analyze the floristic patterns and geographical elements of Hainan and examine the affinity and evolution of the Hainan flora. He also wanted to provide biogepgraphical evidence for the origin of the island. 

The botanist recognized a total of 3894 native seed plant species from 1283 genera and 196 families from Hainan Island. The floristic composition of Hainan revealed that it was tropical in nature. 

Among the 19 genera endemic or approximately endemic to China, only seven are endemic to Hainan. The very low endemism of the flora indicated that Hianan Island had a continental origin, compared with other tropical islands. Hainan Island had more floristic similarities to Vietnam and Guangxi at the family and generic levels than its nearest part of the mainland, Guangdong. Hainan had also the highest proportion of mammals shared with Vietnam, and the lowest proportion with Guangdong. 

The disharmonic flora of Hainan Island revealed that its present location was not its original site. The researcher deduced that Hainan Island could have been in contact with northern Vietnam and Guangxi at least in Eocene.

Palaeobotanical studies suggest that Hainan Island could have been in a much more northerly location with a subtropical climate in the Eocene. It supports the deduction that Hainan could have been adjacent to Vietnam and Guangxi. The research results also support the suggestion from palaeomagnetic and volcanism studies that the Qiongzhou strait could have been formed by an active rift structure, and Hainan drifted to the present location by moving southeast from a higher latitude. 

The study entitled “Biogeographical Evidences Help Revealing the Origin of Hainan Island” has been published in PLoS ONE.