Joint-vetch

Aeschynomene americana, the shyleaf or American joint-vetch, is an annual or short-lived perennial herb to subshrub in the legume family (Fabaceae), native to the tropical and warm-temperate Americas from the southern United States and Mexico through the Caribbean and Central America to South America, with introductions in Africa, Asia, and Australia. Plants produce erect to ascending, branched stems 0.5-2 meters tall, often somewhat woody at the base; the stems are characteristically covered with stiff glandular bristles or short prickle-like hairs. The leaves are alternate, sensitive, paripinnate, 4-10 cm long, with 20-60 pairs of small narrowly oblong leaflets 4-10 mm long that fold together rapidly when touched or at nightfall — a sensitive-plant behaviour shared with several other legumes. Inflorescences are short axillary racemes of 2-6 small pea-flowers; each flower is 5-10 mm long with a pale yellow to pinkish standard streaked with reddish lines. The fruit is a flattened jointed legume (loment) 2-5 cm long, of 4-10 single-seeded segments that break apart at the constrictions; segments are reticulately veined and sometimes spiny. The species favours moist disturbed ground, pasture margins, and roadside ditches.