我国西沙群岛植物区系地理的研究

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

本文通过实地调查,概述了西沙群岛植物区系的组成、特点及其与邻近区系的关系,并对区系的形成与演化过程作了分析。

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,scrub forest and beach vegetation.The dominant species of the forest commu- nities are Pisonia grandis,Guettarda speciosa,Scaevola sericea and Messerschmidia argentea.There are 212 species of wild vascular plants belonging to 52 families and 147 genera in this area,of which there are 4 families,4 genera and 5 species of pteridophytes 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 communi- ties.In this area there is no species endemic to itself.Many primitive taxa such as Gym- nosperms,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 these of Hainan Island.The similarity indices of genera and species are 98.46% and 94.09% respective- ly.Indigofera chuniana is endemic to the two regions.