Bristly starbur

Acanthospermum hispidum DC. (Asteraceae), bristly starbur or goathead burr, is an erect, much-branched annual herb 20-80 cm tall, native to tropical South America but now a pantropical weed of disturbed ground, pastures, and roadsides. The stems and leaves are densely covered with stiff hispid hairs. Leaves are opposite, sessile, broadly ovate to rhombic, 2-7 cm long, with coarsely toothed margins, three prominent veins and rough surfaces. Small yellow flower heads about 5 mm wide are borne singly in leaf axils; each contains a few ray and disc florets. The distinctive fruit is a wedge-shaped, woody achene 5-9 mm long armed with two divergent terminal spines and numerous shorter recurved bristles that cling tenaciously to clothing, fur and skin. It tolerates poor sandy soils and drought, reproducing prolifically by seed and dispersing as a hitchhiker on animals and footwear.