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.
Infrequent throughout the state, although there are no records from the dune area or the extreme northern counties. It is found in both moist and very dry, sandy places. I have never seen it abundant, only once common over a small area, and only once in a cultivated field. All of my specimens are from open woodland and along railroads and canals.