Hainan Island, locating at south China and the north edge of tropical Asia, is an island with an area of 34,000 km². Hainan Island harbors vast rainforests with high levels of biodiversity, with more than 5000 vascular plants among which ~ 500 are endemic to this island. Such rich biodiversity is mainly due to its high mountains, spatial-temporal dynamics in rainfalls associated with monsoons, and habitat heterogeneity caused by different types of soils and rocks. About 400 km² of karst (limestone landscape) were found on Hainan Island, largely distributed at the west and south part of this mountainous island. Totally about 1500 vascular plants in 181 families (750 genera) can be found in karst regions on Hainan Island, of which 65 species are Hainan-endemic. The karst flora on this island is largely pantropical, with some belong to temperate zone. There are 27 plant species on Hainan’s karst regions are included into national or provincial protection lists as endangered or rare species.