A STUDY ON THE FLORISTIC PLANT GEOGRAPHY OF XISHA ISLANDS, SOUTH CHINA

Key words: 
• Xisha Islands /
• floristic plant geography

Abstract: Xisha Islands is situated on the South China Sea, at 15° 46'-17° 08'N. and 111° 11'-112 ° 54'E., with an altitude of 2.6-15.9m. The major types of vegetation are the evergreen coral island forest, and beach vegetation. The major types of vegetation are the evergreen coral island forest, scrub forest and beach vegetation. The dominant species of the forest communities are Pisonia grandis, Guettarda speciosa, Scaevola sericea and Messer schmidia argentea.There are 212 species of wild vascularplants belonging to 52 families and 147 genera in this area, of which there are 4 families, 4 genera and 5 species of pteridophyte and 48 families, 143 genera and 207 species of Angiosperms. The main families of the flora are Poaceae, Papilionaceae, Cyperaceae, Euphorbiaceae, Malvaceae, Rubiaceae, Nyctaginaceae and Boraginaceae etc. According to the geographical distribution, Spermatophytic genera in Xisha Islands may be classified into 9 types, of which pantropic genera accounts for 70% of total genera. At specific level, elements of Tropical Asia to Tropical Australia are dominant part in the forest communities. In this area there is no species endemic to itself. Many primitive taxa such as Gymnosperms, Anonaceae and many others are not found in the flora. Comparing the composition of the flora with those of 6 neighboring regions, the flora of Xisha Islands is quite similar to those of Hainan Island. The similarity indices of genera and species are 98.46% and 94.09% respectively. Indigofera chunianais endemic to the two regions.