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.

Glabrous annual 2-7 dm; lvs lanceolate, long-acuminate, serrate, often with 1 or 2 prominent lateral lobes, the blade 4-12 cm נ7-20 mm, attenuate into a slender or wing-margined petiole 1-3.5 cm; heads erect, discoid or shortly radiate, subcylindric to narrowly campanulate, the disk 5-12 mm wide, the fls 7-30; outer invol bracts mostly 3-5, foliaceous, narrow, erect and surpassing the disk; achenes flat or compressed-quadrangular, ±striate and with a strong median rib on each face, smooth except for a few scattered appressed hairs, 6-11 נ1-2 mm; pappus of 2-4 retrorsely or antrorsely barbed awns, mostly less than half as long as the achene, sometimes much reduced; 2n=48. Estuaries; Que. to N.Y. Aug., Sept.

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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