Annuals, (10-)25-70(-150) cm. Leaves: petioles (narrowly, if at all, winged) 10-35+ mm; blades lance-ovate to lanceolate, (20-)35-100+ × 5-25+ mm, sometimes with 1-4 lobes near bases, bases cuneate, margins serrate, seldom ciliate, apices attenuate, faces glabrous. Heads borne singly or in 2s or 3s. Peduncles 10-35+ mm. Calyculi of (2-)3-5 ± erect, oblanceolate to linear, ± foliaceous bractlets or bracts 7-25(-70+) mm, margins sometimes obscurely ciliate, abaxial faces glabrous. Involucres usually cylindric to campanulate, rarely hemispheric, (4-)8-10(-12) × (4-)7-9 mm. Phyllaries 5-6, oblong to lance-ovate, 8-13 mm. Ray florets usually 0, sometimes 1-3+; laminae yellow-orange, 2-5(-10) mm. Disc florets 7-30+; corollas yellowish, 2.5-3.5 mm. Cypselae blackish to purplish or red-brown, ± flattened, sometimes 3-4-angled, narrowly oblanceolate, outer 5.5-10 mm, inner 6.5-11 mm, margins barbed or ciliate (proximally antrorsely, distally retrorsely), apices ± truncate, faces ± 1-nerved, glabrous or sparsely setulose, often ± striate and/or tuberculate; pappi of 2-4(-5) erect to spreading, antrorsely or retrorsely barbed awns 3-4.5 mm. 2n = 48. Flowering Sep-Oct. Borders of estuaries, marshes, tidal flats; 0-10 m; N.B., P.E.I., Que.; Conn., Maine, Mass., N.J., N.Y., R.I. Bidens eatonii may be better treated as part of B. tripartita.