PUNCTUREVINE, Tribulus terrestris L. 1, plant; 2, seed pod showing burs. Annual, reproducing by seeds. Root system simple taproot. Stems hairy, prostrate, branching from base to form dense mats of slender trailing branches 6 to 8 feet (1.8 to 2.4 m) long. Leaves oblong, opposite, hairy, divided into pinnate leaflets. Flowers small, yellow, 5-petaled, produced in axils of leaves. Seed pods contain 5 burs, each having 2 sharp, long, stout, rough spines, strong enough to penetrate shoe soles or bicycle tires. Burs separate as they mature and often lie in the soil for years before germinating. Found in pastures, roadsides, and waste places, along railroad tracks, and sometimes in cultivated fields. A serious weed, listed as noxious in some states. Cattle do not graze areas infested with puncturevine.