Bidens connata

Bidens connata, commonly known as purple-stemmed beggarticks or swamp beggarticks, is an annual herb in the family Asteraceae native to eastern and central North America and now naturalised across much of Europe and eastern Asia. It grows 0.3-1.5 m tall on damp, often shaded ground beside ponds, sluggish streams, ditches, and seasonally flooded swamps. The stems are usually distinctly purple-tinged, four-angled, glabrous, and well-branched above. The opposite, lanceolate to oblong-lanceolate leaves are 4-15 cm long, sharply serrate, and generally simple although the lowest pair may be three-lobed; petioles are narrowly winged. From late summer into autumn the plants bear small, erect, discoid flower heads 6-12 mm wide of yellow to orange disc florets, usually without obvious ray florets, surrounded by a calyx-like row of leafy outer involucral bracts. The flattened achenes carry two to four barbed awns that adhere readily to clothing.