Fraxinus L. is one of the 24 genera in Oleaceae family and comprises 43 species that are distributed in northern hemisphere. Two species: F. excelsior L. and F. angustifolia Vahl. are reported from Iran. These species are very similar on the basis of morphological characteristics which make their identification difficult. In order to overcome the ambiguity of these two species and their subspecific ranks, morphological and micromorphological traits of the species in 55 populations were studied. Forty nine qualitative and quantitative morphological characteristics were studied. Phenetic analysis was carried out using SPSS ver. 16 software and phenogram of the species considering morphological characters were plotted. Furthermore, PCA analysis was carried out and the most variable characters were determined. Factor analysis revealed the color of adaxial and abaxial surfaces of leaflets, color of winter buds, type of inflorescence, shape of fruit and its tip, and margin of leaflets are the most effective separating characters. According to descriptive analysis, three factors including the type of inflorescence, color of winter bud and shape of the margin serration of the leaflets are the most important ones. Micromorphological studies using scanning electron microscope, revealed two types of trichomes: acicular and capitate. Pollen grains in all specimens are monad and tricolpate. An identification key was prepared using morphological and micromorphological features.

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