Crotalaria juncea is an erect, herbaceous, laxly branched annual, 1-3.5 m tall. The stems are cylindrical and ribbed, pubescent, up to 2 cm in diameter; vegetative parts covered with short, downy hairs. Long, strong taproot, well-developed lateral roots, and multibranched and lobed nodules, up to 2.5 cm in length. Leaves simple with minute, pointed stipules; petiole entire, short, about 5 mm long with pulvinus blade, linear elliptic to oblong, 4-12 x 0.5-3, bright green. Inflorescence a lax, terminal raceme, up to 25 cm long; flowers conspicuous, small with 5 hairy sepals, shortly united at base, lobes pointed, with 3 lower sepals united at tips, separating in fruit; petals deep yellow, standard erect, about 2.5 cm in diameter, rounded, sometimes streaked purple on dorsal surface, wings shorter and keel twisted. Pods cylindrical, 3-6 x 1-2 cm, tomentose, light brown, containing about 6 seeds. Seed heart-shaped, with narrow end strongly incurved, up to 6 mm long, dark brown to black. The genus name ‘Crotalaria’, meaning rattle, is indicative of the noise made by the seeds shaken in the mature pods. The species name was given by Linnaeus because the plant’s green, rushlike, scantily leaved branches resemble Spartium junceaum L., the Spanish broom of the Mediterranean region.