The aim of this study was to identify the ecological species groups and investigate the diversity among them. The research area comprises a wetland system of Boujagh National Park, in Northern of Guilan Province, Iran. Vegetation sampling was carried out by 44 sample plots placed within the different zones in a stratified random manner. In each sampled plot, the cover percentage value of each species was estimated using Bran-Blanquet scales. Vegetation was classified using Two-Way Indicator Species Analysis (TWINSPAN). Classification of plots showed four vegetation groups: “Ceratophyllum demersum-Nelumbo nucifera, Juncus acutus-Rubus sanctus, Mentha aquatica-Phragmites australis, Hydrocotyle vulgaris-Phragmites australis”. Plant diversity in these vegetation groups has been evaluated.The comparison of diversity indices among groups was performed with ANOVA test. Results of analysis of variance in species diversity indices showed significant differences among the groups in terms of some biodiversity indices. The survey of variation in the groups showed that group 3 had the highest value and group1 had the lowest in Fisher’s diversity indices and Menhinink’s and Margalef’s richness indices, respectively. In Sheldon’s evenness index group1 had the highest and group 2 had the lowest measure. Finally, the overall survey of indices showed that despite the high richness and diversity in groups 3 and 2, evenness of these groups was less than group 1 showing the lowest richness and diversity.
