Plants trees or shrubs, often colonial by root suckers. Bark thick, furrowed and often with a network of slender ridges, gray to reddish brown or nearly black. Twigs slender, angled in cross-section, usually zigzag, sometimes armed with spines, variously hairy to glabrous, the winter buds sunken in the stem. Leaves often drooping and folding at night, odd-pinnately compound, short-petiolate, the leaflets 7–19, mostly opposite or subopposite. Stipules slender, papery, and shed with age or modified into spines and persistent; stipels present but shed early, hairlike or linear to very narrowly triangular. Leaflets ovate or oblong-ovate to oblong-elliptic or nearly circular, mostly short-stalked, rounded at the base, rounded at the tip but usually with a minute sharply pointed extension of the midvein, the margins entire, the surfaces hairy, at least when young. Inflorescences axillary racemes with (3)4–30 flowers, pendant, the stalk and axis variously hairy and sometimes also glandular, the flowers not subtended by bracts. Calyces appearing somewhat 2-lipped, the tube shorter than to longer than the lobes, cup-shaped to more or less bell-shaped, the lobes broadly to narrowly triangular, the upper 2 lobes partially fused. Corollas papilionaceous, glabrous or nearly so at maturity, white or pink to purple, the petals cordate or abruptly tapered to a stalklike base, the banner rounded or notched at the tip, abruptly arched upward toward the midpoint, the wings asymmetrically obovate, appearing curved, twisted above the stalk, the keel obovate, boat-shaped, strongly curved upward. Stamens 10, 9 of the filaments fused nearly to the tip and 1 filament free or fused only below the midpoint, the anthers small, attached at the base, all similar in size. Ovary oblong, nearly sessile, glabrous to glandular-hairy, the style bearded toward the tip, the stigma terminal and capitate, hairy. Fruits (when produced) legumes, narrowly oblong, slightly or strongly flattened, very short-stalked at the base, short-tapered to a bluntly or sharply pointed tip, sometimes short-beaked, the margins more or less parallel or irregularly indented between some of the seeds, glabrous or variously hairy and/or glandular, papery to leathery or slightly woody in texture, dehiscent, with 3–10 seeds (or the ovules aborting). Seeds ellipsoid to somewhat kidney-shaped, somewhat flattened, the surfaces brown to reddish brown or dark brown, often somewhat purplish-mottled, somewhat shiny. Four species, southeastern and western U.S. and adjacent Mexico; introduced farther north in North America and in the Old World.

The complex cytology and widespread cultivation of some members of Robinia has led to the naming of numerous additional species. Isely and Peabody (1984) and Lavin and Sousa S. (1995) accepted only the four basic biological elements within the genus as species.