1. Ulmus alata Michx. (winged elm, wahoo)

Pl. 569 n, o; Map 2663

Plants shrubs or trees, 2–15(–30) m tall. Twigs dark brown to purplish brown, usually hairy; almost always at least some of them with 1 or 2, opposite, flat, thin, corky wings. Winter buds 2.5–3.0 mm long, narrowly ovoid to more or less conic, sharply pointed, dark brown to purplish brown or nearly black, minutely pubescent with white or off-white hairs. Petioles 1.5–4.0 mm long. Leaf blades 2–10 cm long, 1–4 cm wide, narrowly elliptic or lanceolate-elliptic, the base nearly asymmetric, gradually tapered to a sharply pointed tip, the major marginal teeth 0.8–1.2(–2.0) mm deep, blunt or more commonly sharp, all or most with 1–3 smaller secondary teeth, the upper surface smooth or slightly roughened, the undersurface short-hairy along and often also between the main veins, not tufted in the vein axils, the secondary veins 10–15 on each side of the midvein, the lateral veins seldom forked toward their tips; juvenile leaves never lobed. Inflorescences short racemes, appearing in the spring before the leaves develop on second-year twigs. Flowers with the stalks 2–7 mm long, the calyces deeply 5-lobed, the tube glabrous, the lobes broadly rounded, glabrous or with a few marginal hairs near their tips. Fruits 0.7–0.8 cm long, 0.2–0.4 cm wide, elliptic to oblong-elliptic or ovate-elliptic, tan, the body and wings densely and finely hairy, the wing margins also densely hairy. 2n = 28. March.

Scattered in the Ozark, Ozark Border, and Mississippi Lowlands Divisions, uncommon or absent elsewhere in the state (eastern [mostly southeastern] U.S. west to Kansas and Texas). Glades, savannas, tops of bluffs, banks of streams and rivers, margins of sinkhole ponds, bottomland forests, mesic to dry upland forests, and sand prairies; also roadsides.

Ulmus alata is most frequently encountered in Missouri as a shrub or small tree in dry upland areas. However, the species can also occur in bottomlands, where it sometimes grows into a mid-story or canopy tree. Trees in wet areas tend to develop fewer corky branches than do those at drier sites.