Acer iranicum (Sapindaceae s. l., Aceroideae), from the upper limits of the lowland forests toward the midlands in the western part of the Hyrcanian forests, is described as new. Diagnostic characters for A. iranicum are sub-leathery to papery leaves, rounded, elongate sepals, oblong-ovate petals, and samara wings diverging at 55–75°. The phylogenetic position of A. iranicum within Acer section Acer is elucidated based on analysis of the ITS data from representatives of all taxa within section Acer and morphological evidence. Acer iranicum was resolved as sister to A. opalus (Italian maple), but quite distant from all other species of maples in Iran.