Though "A. rubrum" is usually easy to identify, it is highly changeable in morphological characteristics. It is a medium to large sized tree, reaching heights of and exceptionally over in the southern Appalachians where conditions favor its growth. The leaves are usually long on a full-grown tree. The trunk diameter often ranges from ; depending on the growing conditions, however, open grown trees can attain diameters of up to . The trunk will remain free of branches until some distance up the tree on forest grown trees, while individuals grown in the open are shorter and thicker with a more rounded crown. Trees on poorer sites often become malformed and scraggly. Generally the crown is irregularly ovoid with ascending whip-like curved shoots. The bark is a pale grey and smooth when the individual is young. As the tree grows the bark becomes darker and cracks into slightly raised long plates. The largest known living red maple is located near Armada, Michigan, at a height of and a bole circumference, at breast height, of .