On the biogeographical origin of Hainan Island in China

Based on biogeographic study of Hainan Island in China, only seven endemic genera and 397 endemic species of flora have been identified (accounting for ~ 10% of total flora), indicating that Hainan has a very low number of endemics and a disharmonic flora. Furthermore, the extremely low endemism is indicative of a continental origin. Although Hainan is closest to Guangdong (~20 km), it has more floristic similarities to Vietnam and Guangxi (China) at the family and genus levels. Of note, only 3.7% of Hainan genera show East Asian distributions. Furthermore, Hainan mammals show a biogeographic pattern similar to that of flora, with the highest proportion of mammals sharing with Vietnam and the lowest proportion sharing with Guangdong. Thus, the disharmonic flora and fauna of Hainan Island suggests that its present location is not its original site, and that the island may have been in contact with northern Vietnam and Guangxi in southwest China. Palaeobotanical studies suggest that Hainan Island may have been in a much more northerly location with a subtropical climate during the Eocene. This supports the deduction that Hainan was, at some point, adjacent to Vietnam and Guangxi. The current results are concordant with palaeomagnetic and volcanism studies, which suggest that the Qiongzhou strait formed by an active rift structure, and Hainan drifted to its present location by moving southeast from higher latitude. The opinion espoused in this paper on the biogeographical origin of Hainan Island has support from other studies on endemic mammals (Hainan gymnure, Mammalia, Lipotyphla), insect genera (Hesperiidae: Pyrginae: Tagiadini), Stedocys spitting spiders, earthworms (Megascolecidae), and other plant taxa.