Amorpha L. (Wilbur, 1975)

Plants shrubs or subshrubs (rarely perennial herbs elsewhere), with thick roots and rhizomes. Stems erect or ascending, unbranched or branched, unarmed, glabrous to densely hairy. Leaves alternate, odd-pinnately compound, subsessile to short-petiolate, aromatic when bruised, the leaflets 9 to numerous, variously alternate to opposite. Stipules inconspicuous but often persistent, 1–2 mm long, linear to hairlike, thin-textured and brown, attached at the base; stipels present, similar to the stipules, shed early. Leaflets ovate to oblong, rounded or angled to a short-stalked base, bluntly to sharply pointed at the tip, often with a minute sharp point (this sometimes gland-tipped) at the very tip, the margins entire, the surfaces variously hairy and gland-dotted, with a midvein and inconspicuous or conspicuous secondary veins. Inflorescences axillary and terminal, ascending to spreading, dense, spikelike racemes, often clustered, short- to moderately stalked, the bracts subtending flowers linear to hairlike and inconspicuous, shed early. Calyces 5-lobed, the lobes much shorter than to about as long as the tube, similar or the lowermost lobe slightly longer than the others. Corollas not papilionaceous, reduced to a solitary banner petal, this tapered to a short stalklike base, obovate to heart-shaped, folded around the stamens and gynoecium, the wing and keel absent. Stamens 10, the filaments all fused near the base, the anthers long-exserted, attached near the midpoint, all similar in size. Ovary ellipsoid to ovoid, sessile, the style slender, glabrous or hairy, the stigma small and terminal. Fruits modified legumes, slightly elongate, slightly flattened, sessile, more or less oblong and usually somewhat curved in outline, often conspicuously gland-dotted, indehiscent, 1-seeded. Seeds oblong-elliptic in outline, usually with a small notch at the attachment end, somewhat flattened, smooth, shiny. About 15 species, North America, most diverse in the U.S.

Amorpha is related to Dalea (Polhill, 1981). The species tend to be variable in degree of pubescence, leaf texture, density of glands, and number and length of racemes. Numerous additional species, varieties, and forms have been recognized in the past, but the general consensus is that most of these do not deserve recognition.