Spanish-needles

Bidens bipinnata, commonly known as Spanish needles, is an erect annual herb of the family Asteraceae, widely naturalized throughout the warm temperate and tropical regions of the world and probably native to the Americas. It typically reaches 30–170 cm in height, with slender, four-angled, sparsely pubescent stems that branch freely in the upper portion. The leaves are opposite, petiolate, and characteristically bipinnately to tripinnately divided into narrow, deeply toothed segments, giving the foliage a feathery, fern-like appearance. The terminal flower heads are small and rather inconspicuous, 6–12 mm across, with three to five short, pale-yellow ray florets surrounding a disk of yellow tubular florets. After flowering, the heads produce slender, four-angled black achenes 10–18 mm long, each tipped with three or four stiff, retrorsely barbed awns that cling readily to clothing and animal fur, providing the plant with its common names and an effective dispersal mechanism. It favours disturbed ground, roadsides, fields and gardens.