Woolly senna

Senna hirsuta, the woolly or hairy senna, is an erect, short-lived shrub or robust herb in the Fabaceae (subfamily Caesalpinioideae) growing 1–3 m tall, with branches densely clothed in long, soft, spreading golden-brown hairs. Leaves are alternate, pinnately compound, 10–25 cm long, bearing 3–8 pairs of opposite, ovate to elliptic leaflets 3–8 cm long with an acute apex and asymmetrical base; both surfaces are softly pubescent. A small, conical or club-shaped gland sits on the petiole between the lowest pair of leaflets. Inflorescences are short, axillary or terminal racemes of bright yellow, slightly zygomorphic flowers about 2 cm across; the five sepals are unequal and the five petals are obovate with conspicuous brown veins. Stamens are 10, of three distinct sizes. The fruit is a flattened, linear pod 10–20 cm long and 0.6–1 cm wide, hairy when young and becoming glabrescent, containing many flattened, glossy brown seeds. It is native to tropical America and naturalized as a weed of disturbed ground throughout the tropics.