In the present study, we investigated the structure of stomata in seven native species of Hyrcanian forests (Acer hyrcanum, A. velutinum Boiss., A. campestre, A. platanoides L., A. cappadocicum, A. monspessulanum, A. amazandaranicum), as well as non-native species that have fully adapted (A. negundo, A. negundo variegatum, and A. palmatum). We used light and electron microscopy to determine the form and position of the stomata in relation to the leaf epidermal cells. The length, width, shape, area, perimeter, and stomatal density were all measured. Our findings revealed that the stomata type of A. negundo varengiayum, A. campestre, A. hyrcanum, A. mazandaranicum and A. monsspesulanum is anomocytic, A. platanoides and A. cappadocicum have anomocytic stomata with wavy subsidiary cells, while A. palmatum has anisocytic stomata and A. velutinum has parasitic stomata. A. negundo has actinocytic stomata. Regarding the location of stomata relative to adjacent epidermal cells, we identified three types. In the first type, the stomata were flush with adjacent epidermal cells (A. cappadocicum, A. negundo, A. platanoides). In the second type, the stomata were higher (A. negundo variegatum), and in the third type, the stomata were lower (A. velutinum, A. monspesulanom, A. campestre, A. mazandaranicum, A. hyrcanum). The principal component analysis was used to determine the essential stomatal traits in differentiating between species. We also investigated the distribution of trees in the coordinate axis space based on two main components and performed cluster analysis based on stomatal characteristics. A. platanoides, A. negundo, A. negundo variegatum were in one cluster, while the other species were in separate clusters. The calculation of dissimilarity among the studied species revealed the lowest similarity between A. negundo and A. hyrcanum and the highest similarity between A. campestre and A. mazandaranicum. The results of the discriminant analysis identified stomatal density as the essential factor in differentiation between the studied species.
