Cocklebur

Description:

"They are coarse, herbaceous annual plants growing to 20-47 in (1.5 to 4 ft) tall. The leaves are spirally arranged, with a deeply toothed margin. Some species, notably X. spinosum, are also very thorny with long, slender spines at the leaf bases. The flowers are of two types; One, in short terminal branches, produces only pollen. The other, in clusters in the axils of the leaves, produces seed. Unlike many other members of the family Asteraceae, whose seeds are airborne with a plume of silky hairs resembling miniature parachutes, cocklebur seeds are produced in a hard, spiny, globose or oval double-chambered, single-seeded bur .32-.79 in long. It is covered with stiff, hooked spines, which sticks to fur and clothing and can be quite difficult to extract. These remarkable burred seeds have allowed this plant to be carried all over the world by unsuspecting travelers. This plant reproduces only by means of its seed." http://en.wikipedia.org/wiki/Cocklebur