Alnus (Alder) is a genus of Betulaceae, which comprises more than 29 species in the world. According to different classifications of flora, eight taxa of the genus naturally grow in Iran and are distributed along the northern slope of Albourz Mountains in Iran (Hyrcanian forests). In the current research, we investigated morphological characteristics and phylogenetic relationships of 31 populations of the genus in Iran. Twenty-eight qualitative and quantitative traits were studied for morphological evaluation and ITS molecular marker was investigated for molecular study. We used MVSP, SPSS, MrBayes, RAXMLGUI, Mesquite 2.71, Modeltest 3.7 software packages for statistical analyses. Morphological features varied widely among the studied taxa and ANOVA test revealed significant difference for most of them. Moreover, the angle of leaf base, the leaf margin shape, the length and width of the leaf blade, fruits length, and the presence of hair on the petioles, young twigs, and buds were more variable morphological traits. The studied taxa were clustered separately in the UPGMA tree, PCA and PCO plots using morphological traits. In addition, CA-joined plot showed each taxon to have distinct morphological trait(s), which is useful in the identification of the taxa. Phylogeny analysis revealed that Alnus genus is a monophyletic group. Furthermore, the studied taxa were clustered separately in phylogenetic dendrogram. According to morphological and ITS data, we listed ten taxa of the genus in Iran and introduced A. hyrcana and A. longiflorescentia as two new species from Hyrcanian forests of Iran.

Alnus Mill. is a problematic genus of Betulaceae, and there are several intrageneric classifications for the genus. Alnus species are widely distributed in the Hyrcanian forest of Iran, and different species with some intraspecific taxonomic ranks including subspecies and varieties have been reported from this country. We evaluate seed micromorphology characteristics of ten taxa using scanning electron microscopy and light microscopy in the current study. The data were analyzed using SPSS and MVSP software. Results revealed that qualitative characteristics such as seed shape, surface sculpturing pattern, presence of indumentum, and its type vary among the studied taxa and have diagnostic value. However, seed color was nearly stable among the taxa. Besides, quantitative variables highly differed among the taxa. In the UPGMA tree, Alnus taxa were clustered into three groups, and these groups were supported by PCA and PCO plots. According to the PCA bi-plot, some taxa were characterized by the particular characteristic(s) that was useful for their identification. In some cases taxa clustering was similar to those of previous phylogenetic and morphological studies. Our findings revealed that seed morphology characteristics are a valuable taxonomical tool in identifying most Alnus taxa, except for A. glutinosa subspecies, which have similar seed morphology features in common.