Annuals, (5-)25-150(-200) cm. Leaves: sessile or petioles (± winged) 5-15(-35+) mm; blades ± elliptic to lanceolate, (20-)40-100(-200+) × 10-30(-70) mm, sometimes laciniately 1-pinnatisect with 1-4+ lobes near bases, bases cuneate, margins entire or dentate to serrate, usually ciliate, apices attenuate, faces glabrous or hirtellous. Heads borne singly or in 2s or 3s. Peduncles 10-35(-80) mm. Calyculi of 2-6+ spreading or ascending, lanceolate, linear, oblanceolate, oblong, or spatulate, ± foliaceous bractlets or bracts 10-25(-35+) mm, margins (entire or serrate) usually ciliate, abaxial faces hispidulous near bases, distally glabrous. Involucres campanulate to hemispheric or broader, (4-)6-12 × (3-)6-9(-15+) mm. Phyllaries (6-)8(-9), elliptic to oblong or ovate, (4-)5-6(-12) mm. Ray florets usually 0, sometimes 1-5+; laminae yellowish, 4-8 mm. Disc florets (5-)20-40(-60+); corollas pale yellow to orange, 2-3 mm (± abruptly ampliate, anthers usually dark, blackish). Cypselae blackish to purplish or brown, usually (at least inner) ± 4-angled, usually cuneate to linear, sometimes ± obpyramidal, outer (3-)4-7 mm, inner (4-)5-8 mm, margins proximally antrorsely to patently, distally retrorsely, barbed, apices ± truncate to concave, faces usually strongly 1-nerved, usually tuberculate, glabrous or setulose; pappi 0, or of (1-)2-4(-6), ± erect to spreading, antrorsely or retrorsely barbed awns (0.2-)2-5 mm. 2n = 48. Flowering Aug-Oct. Marshes and other wet sites; 10-1700 m; N.B., Nfld. and Labr. (Nfld.), N.S., Ont., P.E.I., Que.; Conn., Del., Ga., Ill., Ind., Iowa, Kans., Ky., Maine, Md., Mass., Mich., Minn., Mo., Mont., Nebr., N.H., N.J., N.Y., N.C., N.Dak., Ohio, Pa., R.I., S.C., S.Dak., Tenn., Va., W.Va., Wis.; Europe; Asia; n Africa; introduced in Pacific Islands, Australia. Bidens connata may be better treated as part of B. tripartita.