DISTINGUISHING CHARACTERISTICS: Leaves once-pinnately compound, opposite, 10 to 12 inches long; leaflets 5 to 9 in number (usually 7), oblong-lanceolate or less commonly elliptic, 2 to 6 inches long, tapering at the base and extending along the upper side of their 1/16- to 3/16-inch-long stalks; margins conspicuously toothed; upper surface dark green and often glossy; lower surface light green, glabrous or nearly so (hairy in the form called red ash). Winter twigs moderate in diameter, gray, glabrous (finely hairy in the form called red ash); leaf scars small, half-round to nearly round, bundle scars numerous and very close together, forming a fine curved line. Buds globose to subglobose, brown, with 1 or 2 pairs of visible scales, the terminal 1/8 to 1/4 inch long. Flowers very small, dioecious, apetalous, appearing with or before leaves; staminate in short, compact panicles, pistillate in open panicles. Fruit a narrow, paddle-shaped samara 1 to 2 inches long that often persists in winter; wing extending along upper half of seed cavity. Bark ashy gray or gray-brown, furrowed, with narrow, interconnecting ridges enclosing diamond-shaped spaces.
SIMILAR TREES: White ash has relatively broad leaflets with entire or obscurely tooth margins and stalks about 1/4 inch long; the wing of its samara does not extend along the sides of the seed cavity. Black ash has 9 to 11 unstalked leaflets and its fruits have indistinct, flattened seed cavities.
IOWA DISTRIBUTION: Native and planted throughout the state.