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Hyrcanian forests in northern Iran have important tree and shrub elements of Euro-Siberian and rare forest communities, among them beech community widely covers the mountainous forests from Western to Eastern (Gorgan) Hyrcanian region. In order to identify the floristic characteristics and affecting factors on the species richness in pure beech stands in Eastern Guilan, using systematic-random method 54 plots were recorded. A total of 111 plant species belonging to 84 genera and 44 families were identified, with Orchidaceae having 9 species and genus Carex with 6 species being the largest family and genus, respectively. The highest frequency inter-species is Galium odoratum, an understory herb species forming communities in different areas of beech forests in Hyrcanian region. Since the studied region is forest and mountainous, hemicryptophytes and geophytes are the most life forms, respectively in these areas and Euro-Siberian elements (with 30.6 %) form the highest frequency from a chorological point of view. Also, the size of the microrelief and percentage of tree cover create different ecological conditions in plots such as moisture retention and change in the amount of incoming light into the plots, which are the most influential factors on species richness of these areas.