Abstract: Many plants are threatened to varying degrees due to frequent land development activities in the eastern coastal areas of Jiangsu. We selected the flora of Guanyun County in Lianyungang City as study object. In order to study the flora and species diversity characteristics of native seed plants in this area, a comprehensive survey method was used in combination with line survey, sampling survey and special area investigation. In addition, the floristic characteristics of this County was compared with those of four surrounding Counties in the eastern coastal area of Jiangsu. The results indicate that:(1) there were 357 species belonging to 240 genera and 72 families of native seed plants in this County. Angiosperms were dominant and gymnosperms were scarce. The diversity of native seed plants species is higher in this Conunty than that of in the adjacent Counties. (2) At the family level, there were 6 areal types of native seed plants, among which the tropical and temperate components accounted for 58.33% and 41.67%, respectively; at the genus level, there were 14 areal types of native seed plants, among which the tropical and temperate components accounted for 37.25% and 61.75%, respectively, and the ratio of tropical genera to temperate genera (R/T value) was 60.32%. (3) Guanyun county has the most abundant herbaceous plant species, and the species richness index (R), Shannon-Wiener diversity index (H) and Simpson dominance index (D) of herbaceous layer were significantly higher than those of the tree layer and shrub layer (P<0.001). (4) From coastal to inland (from east to west), with the increase of the distance from the sea, the species richness index (R) of herbaceous plants increased significantly (P<0.05), while the Pielou evenness index (J) of herbaceous plants decreased significantly (P<0.001). (5) There was high species diversity in the central and western parts of Guanyun County, especially in Yilu mountain and Dayi mountain and their surrounding areas, which were the key areas for biodiversity conservation. (6) the similarity coefficients (S_C) of native seed plants genera between Guanyun County and its four surrounding areas of Northern Jiangsu Plain were all above 50%, and the similarity coefficient of native seed plants flora of Guanyun County with Guannan County was the highest (S_C=61.96%). Guanyun county is an important part of the eastern coastal area of Jiangsu Province. This study provides the foundational data for effective conservation, scientific management and sustainable utilization of native plant diversity in Guanyun County.

Key words: eastern coastal area of Jiangsu, flora, Guanyun County, native seed plants, similarity coefficient, species diversity