Abstract: The Zhoushan Archipelago, one of the famous fishing grounds in China, is lo cated in the northern part of the Donghai Sea, at the mouth of the Hangzhou Bay (Fig. 1). The flora of the archipelago was botanically little known. After 1972, several botanical ex plorations to the archipelago were conducted by Qiu L.-Q. of the Shanghai Museum of Natu ral History, and nearly one thousand numbers of plant specimens were collected. From these specimens, we have identified about 500 species of seed plants. The present paper deals with a numerical taxonomic study of the floristic affinities of seed plants of the Zhoushan Archipelago by means of both cluster and principal component analyses (PCA). The total distribution realm of the Zhoushan floristic elements is divided into 18 regions, which were used as Operational Taxonomic Units (OTU). The 348 native species and infrasp ecific taxa (see Appendix 1, excluding cultivated plants, ruderals and exotics) of seed plants were used as characters of the OTUs, A normal cluster analysis using UPGMA gave rise to phenogram (Fig. 1). The phenogram provides a great amount of information regarding the floristic affinities between Zhoushan and the other regions. In the PCA, method of inverse analysis was used and has brought forth two diagrams of dimensional program (Fig. 2a,b). These diagrams give some hints of the distributional trends of geographical elements and floristic affinities. The result of the above analyses shows that the floristics of the Zhoushan Archipelago is the most closely related to those of its neibouring regions, for instance, Zhejiang mainland, Jiangsu and some other regions of eastern China. Though rich in island elements, the archipelago has almost no endemic species. The short distance between the archipelago and the mainland, which has favored mutual exchange of plants, and the severe destruction of the original forest vegetation, may account for this phenomenon. The floristic similarities between Zhoushan and Taiwan of China and between the archipelago and Japan are not so remarkable. This may be due to both the climatical difference and geographical barriers existing between these floristic regions. Yet the presence of a number of linking plants confined to these floras, such as Rhaphiolepis integerrima, Anodendron salicifolium, and Eurya japonica, etc., suggests that these regions should be considered as being of the common tertiary origin. The mountain forest flora of Zhoushan is more closely related to those of southern regions than to those of northern regions of China, From the point of view of floristic regionalization, it is appropriate to consider the flora of the Zhoushan Archipelago as a part of the northern subregion of the mid-subtropical region.

Key words: The Zhoushan Archipelago, Floristics, Numerical study