Sesbania Scop.

Plants annual (perennial herbs, shrubs, and trees elsewhere), with taproots. Stems erect, unbranched or less commonly branched from above the midpoint, unarmed, glabrous or with short appressed hairs lacking a bulbous base. Leaves often drooping and folding at night, even-pinnately compound, short-petiolate, the leaflets 16 to numerous, opposite. Stipules 4–10 mm long, linear, herbaceous to more commonly papery, appearing basally attached, persistent or shed early, the stipels minute, inconspicuous. Leaflets narrowly elliptic to oblong or occasionally linear, sessile or nearly so, angled or rounded at the base, rounded at the tip but usually with a minute sharply pointed extension of the midvein, the margins entire, the surfaces glabrous or less commonly with short appressed hairs, the undersurface sometimes purplish-tinged. Inflorescences axillary racemes or loose clusters with 2–7(–10) flowers, spreading to somewhat pendant, the stalk and axis glabrous or occasionally with sparse short appressed hairs lacking a bulbous base, the flower stalks subtended by linear bracts 3–6 mm long, these shed early, each flower also closely subtended by a pair of narrowly triangular bractlets 3–4 mm long, these also shed early. Calyces with the tube 3–4 mm long, broadly bell-shaped, glabrous, the lobes absent or shorter than the tube, triangular, and slightly unequal. Corollas papilionaceous, glabrous, yellow to greenish yellow, sometimes streaked or tinged with red or purple, the banner nearly circular above the stalklike base, shallowly notched at the tip, abruptly arched upward above the midpoint, the wings asymmetrically obovate, appearing somewhat curved, the keel boat-shaped and somewhat curved upward. Stamens 10, 9 of the filaments fused nearly to the tip and 1 filament fused below the midpoint, the anthers small, attached at the base, all similar in size. Ovary oblong to nearly linear, short-stalked, the style curved, glabrous, the stigma terminal and capitate. Fruits legumes, variously shaped, not or slightly flattened, stalked at the base, tapered to a prominent beak at the tip, the margins variously shaped, glabrous, papery to leathery in texture, dehiscent only with age, (1)2- or (15–)20–40-seeded. Seeds, broadly ellipsoid to oblong-ellipsoid, somewhat flattened, the surface brown, sometimes mottled with purplish brown, smooth. About 60 species, nearly worldwide, mostly in tropical and warm-temperate regions.

The two species of Sesbania recorded from Missouri are very similar in habit and vegetative features, although S. herbacea tends to have more leaflets than does S. vesicaria.