Sheepbur

Acanthospermum australe, commonly called sheepbur, Paraguay starbur or spiny-bur, is a prostrate to weakly ascending annual or short-lived perennial herb in the family Asteraceae native to tropical and subtropical South America, particularly the lowlands of Brazil, Paraguay, Argentina and Bolivia. It has become naturalised as a weed of disturbed ground, pastures, roadsides and crops in many warm regions worldwide. The plant forms a low, spreading mat with hairy, often reddish stems 20 to 80 centimetres long. The leaves are opposite, obovate to rhombic, 2 to 6 centimetres long, with shallowly toothed margins and short, soft hairs on both surfaces. Small, inconspicuous yellow flower heads are borne singly in the leaf axils and produce the species' most distinctive feature: hard, wedge-shaped to triangular burs armed with two stout divergent terminal spines and several smaller marginal hooked spines. The burs cling tenaciously to fur, wool and clothing, providing very effective epizoochorous dispersal.