Bidens pilosa

B. pilosa seedlings have lanceolate (strap-shaped) cotyledons, 25 mm long, and purple-tinged hypocotyls. The first true leaf is similar to later leaves. Finot et al. (1996) describe the morphology of dry seed, unfolded cotyledons, first true leaf or leaf pair unfolded and two to five true leaves unfolded. Original drawings and photographs accompany each description.
The plant is an erect annual herb, 20–150 cm tall (in tall plants sometimes the branches straggling), very variable, reproducing by seeds. Main root pivotant. Stems square, glabrous or minutely hairy, green or with brown strips. Dark green, opposite leaves on stems and branches, 4–20 cm long, up to 6 cm wide, the lower leaves simple, ovate and serrate, the upper leaves trifoliolate or imparipinnate with 2–3 pairs of pinnae and a single terminal leaflet. Petioles are 2–5 cm long.
The inflorescence is an isolated or grouped pedunculated capitula, emerging from the leaf axil. Heads borne singly at the ends of long, slender, nearly leafless branches;narrow, discoid, the disk 4-6 mm wide at anthesis;ray florets, absent or 4–7 per head, white or pale-yellow, 2–8 mm long, disk florets, 35–75 per head, yellow.
Achenes (commonly referred to as 'seeds') linear, black or dark brown, 1–1.5 cm long, flat, 4-angled, sparsely hairy. Pappus with 2–3(–5) yellowish barbed awns, 1–2 mm long. The achenes are the dispersal units;dispersion is aided by the awns as they readily attach to animal skin, machinery and clothing.