Beggar-ticks

Bidens frondosa (devil's beggar-ticks, sticktight) is an erect, branching annual herb of the daisy family (Asteraceae), typically growing 20–60 cm tall and occasionally reaching 1.8 m on moist, fertile sites. The slender, four-angled to square, smooth or slightly hairy stems often turn purplish and branch freely toward the top. The opposite, long-petioled leaves are pinnately divided into three to five lance-shaped to triangular, coarsely toothed leaflets each 4–10 cm long with sharply pointed tips. From midsummer to autumn the plant produces solitary or few-clustered erect flower heads about 1–1.5 cm across at the branch tips, surrounded by a conspicuous outer involucre of 6–10 spreading green leafy bracts much longer than the head itself; the heads usually consist only of numerous orange-yellow tubular disc florets, with ray florets absent or reduced to a few inconspicuous yellow rays. The fruit is a flat, blackish-brown, wedge-shaped barbed achene (cypsela) up to 1 cm long topped by two stiff downward-barbed awns that cling readily to fur and clothing. Native to most of Canada and the contiguous United States, it has been widely introduced across Europe and Asia where it colonises moist disturbed soils, riverbanks, ditches, and wet meadows.