Abstract:

Hainan Island offers an excellent opportunity to study biodiversity and biogeography as it is the biggest tropical island in China while its flora evolution and biogeographic patterns have remained largely unexplored. Gesneriaceae is a typical tropical plant family, showing diversification centers in southwestern China and the Malay Archipelago. Hainan Island is located between these two ‘hotspots’. In this study, area-adjusted species density and endemic indices of Gesneriaceae on Hainan Island were compared with nearby regions including Guangdong, Guangxi, Yunnan, Guizhou, and Vietnam. The detailed distribution patterns of Gesneriaceae on Hainan Island were also explored by comparing species diversity and endemic proportions among different mountains and altitudes. We also used nuclear ITS1/2 and chloroplast trnL-F sequences to construct a phylogenetic tree of Gesneriaceae on Hainan Island to study dispersal histories and the speciation time of Hainan-endemic species. Our results showed that, although Hainan Island has only 24 Gesneriaceae species, of which eight species and two genera are endemic, it also was characterized by a very high area-adjusted species diversity and endemic index due to its small geographical area. Hainan Gesneriaceae were distributed mainly in high mountainous regions such as Mt. Wuzhi, Mt. Jianfeng, and Mt. Yingge and showed the highest species diversity at both 400-1,000 m and >1,400 m a.s.l. The molecular data showed that two endemic monotypic genera, i.e. Metapetrocosme and Cathayanthe, evolved at about 12 Ma, which may have been triggered by the monsoon climate (formed at about 28 Ma). Hainan contains the most basal taxa of Asian Gesneriaceae and shared these with Southeast Asia, suggesting Hainan Gesneriaceae largely originated from Southeast Asia, instead of the Chinese mainland. However, the great similarity of species composition between Hainan Island and the geographically-closest province, i.e. Guangdong, proves that Hainan flora experienced frequent species exchanges with the Chinese mainland recently, likely during the late Tertiary (~3 Ma) when the island was connected with the Chinese mainland.

Key words: species diversity, endemic species, geographic distribution, species dispersal, molecular phylogeny