Annuals, (15-)30-100(-150+) cm. Leaves: petioles 20-50 mm; blades rounded-deltate to ovate or lanceolate overall, (20-)30-70+ × (20-)30-60+ mm, (1-)2(-3)-pinnatisect, ultimate lobes obovate or lanceolate, 15-45+ × 10-25+ mm, bases truncate to cuneate, ultimate margins entire, sometimes ciliolate, apices rounded to acute or attenuate, faces usually glabrous, sometimes hirtellous. Heads usually borne singly, sometimes in ± corymbiform arrays. Peduncles (10-)20-50(-100) mm. Calyculi of (7-)8(-10) linear bractlets 3-5 mm, ± appressed, margins ciliate, abaxial faces usually glabrous. Involucres ± campanulate, 5-7 × 3-4(-5) mm. Phyllaries 8-12, lanceolate to linear, 4-6 mm. Ray florets 0 or 3-5+; laminae yellowish or whitish, 1-2(-3) mm. Disc florets 10-20(-30+); corollas yellowish to whitish, 2-3 mm. Cypselae red-brown, outer weakly obcompressed, 7-15 mm, inner ± 4-angled, linear to linear-fusiform, 12-18 mm, margins not ciliate, apices ± attenuate, faces 2-grooved, often tuberculate-hispidulous; pappi of (2-)3-4, erect to divergent, retrorsely barbed awns 2-4 mm. 2n = 24, 72. Flowering (Jun-)Aug-Sep(-Oct). Fields, forests, disturbed, wettish sites; 10-1800 m; N.B., Ont.; Ala., Ariz., Ark., Conn., D.C., Fla., Ga., Ill., Ind., Iowa, Kans., Ky., La., Md., Miss., Mo., Nebr., N.J., N.Mex., N.Y., N.C., Ohio, Okla., Pa., R.I., S.C., Tenn., Tex., Va., W.Va.; South America; Europe; Asia; Pacific Islands. Bidens bipinnata is probably native in eastern Asia and introduced in South America, Europe, Asia, and Pacific Islands.
Glabrous or minutely hairy annual 3-17 dm; lvs 4-20 cm including the 2-5 cm petiole, mostly 2-3 times pinnately dissected, the ultimate segments tending to be rounded; heads narrow, disciform, the disk only 4-6 mm wide at anthesis, the short, ochroleucous rays not surpassing the disk; outer invol bracts 7-10, linear, ±acute, not evidently expanded upwards, shorter than the inner; achenes linear, tetragonal, narrowed above, often sparsely hairy, 10-13 mm, or some of the outer shorter; pappus of (2)3 or 4 yellowish awns; 2n=24, 72. Moist to fairly dry, disturbed habitats; Mass. to Fla., w. to Neb., Calif., and Mex., e. Asia. July-Oct.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
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