9. Bidens trichosperma (Michx.) Britton

Coreopsis trichosperma Michx.

B. coronata (L.) Britton (1913), not B. coronata Fisch. ex Colla (1834)

Pl. 273 e, f; Map 1157

Plants annual or biennial, terrestrial, sometimes with taproots. Stems 15–80(–150) cm, erect or ascending, glabrous or nearly so. Leaves all more or less similar, short-petiolate, opposite, the blade 2–12 cm long, mostly ovate or triangular-ovate in outline, 1 or 2 times deeply pinnately divided or compound into 3–7(–9) segments or leaflets, these linear to more commonly lanceolate to oblanceolate, angled or tapered at the base, the middle one frequently with a stalklike base, tapered to a sharply pointed tip, the margins usually sharply and finely to coarsely toothed, rarely entire or nearly so, the surfaces glabrous or sparsely hairy. Inflorescences of solitary terminal heads or appearing in loose, open clusters or small panicles, the heads radiate, not nodding at fruiting. Involucre with the outer series of (6–)8(–11) bracts 4–8 mm long, ascending to spreading, somewhat leaflike, linear to narrowly oblanceolate, the margins entire but sometimes with minute, ascending hairs, the surfaces glabrous; the inner series of 6–8 bracts 4–8 mm long, oblong-elliptic, glabrous. Chaffy bracts narrowly oblong-lanceolate, usually with broad, yellowish margins and tip, occasionally purplish-tinged at the tip. Ray florets (6–)8(–9), the corolla showy, 10–25 mm long, yellow. Disc florets 40–80(–120), the corollas 3–5 mm long, yellow. Pappus of 2 awns 1–4 mm long (rarely shorter and scalelike), these with upward barbs, erect to somewhat spreading at fruiting. Fruits 4–8 mm long, narrowly wedge-shaped to oblong-oblanceolate or nearly linear (mostly 2.5–5.0 times as long as wide), more or less flattened and somewhat 4-angled in cross-section, the angles roughened with short, stiff, ascending, pustular-based hairs, the faces sometimes with 1 or few faint longitudinal line(s), dark brown to black, sparsely to moderately pubescent with short, fine, mostly appressed hairs. 2n=24. August–October.

Introduced, known thus far only from the city of St. Louis (eastern [mostly northeastern] U.S. west to Minnesota, Nebraska, and Mississippi). Railroads.

This species was first reported for Missouri by Mühlenbach (1979).