Abstract:South China Sea islands consist of more than 1130 islands with total area of approximately 35000 km2.The highest mountain in Hainan Island is Wuzhi Shan, the highest peak being 1867.1 m.The major vegetation types in the islands include tropical rain forests, tropical monsoon forests,tropical coniferous forests,mangroves, tropical coral reef island evergreen forests,shrub forests, shrubby grassland and beach vegetation.There are 3584 species (including infr4specific ranks) of spermatophytes belonging to 182 families (according to Engler System) and 1238 genera in these islands.The main families with more than 50 species are Gramineae,Leguminosae,Orchidaceae,Rubiaceae,Euphorbiaceae, Cyperaceae, Compositae, Lauraceae,Asclepiadaceae,Labiatae,Moraceae,Fagaceae, Verbenaceae, Acanthaceae, Urticaceae,Annonaceae,Theaceae and Myrtaceae.The main genera with more than 20 species are Ficus,Ilex,Syzygium,Fimbristylis,Hedyotis,Ardisia, Symplocos, Lithocarpus, Crotalaria,Cyperus. Diospyros and Carex,and most of them are of tropical and wide distribution.According to the geographical distribution,the spermatophyte genera of South China Sea Islands may be divided into 14 types and 14 subtypes, of which Tropical Asia and Pantropic elements are the main ones in the flora, and the temperate elements are relatively poor. At specific level,the Tropical Asia elements has a higher percentage,amounting to 47.49% of the total species.In this area there are 19 genera endemic to China, of which 9 genera are endemic only to South China Sea islands,and 1183 species are endemic to China, of which 523 species endemic to South China Sea Islands, some of them are the dominant species in their communities.Comparing the composition of the flora with those of 5 neighbouring regions, the flora of South China Sea islands is quite similar to those of Indo-China Peninsula and Guangdong mainland, the indices of genera similarity to Indo-China Peninsula and Guangdong mainland are 84.3% and 82.3% respectively.South China Sea islands is a part of Cathaysian ancient land, and its flora naturally belongs to the Cathaysia flora,but posseses its own characteristics.Some plants distributed from Australia northward through southeast Asia to South China Sea islands,but never reached the mainland of China.The substitute phenomenon and flora division have been also discussed in present paper.
