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.