Annuals, 10-90+ cm. Leaves: petioles 10-25 mm; blades lanceolate to lance-linear, 40-160 × 3-30+ mm, bases cuneate, margins entire or laciniate to serrate or denticulate, minutely, if at all, ciliate, apices acuminate to attenuate, faces glabrous. Heads usually borne singly, sometimes in open, ± corymbiform arrays. Peduncles 10-30(-60+) mm. Calyculi of 3-5 usually spreading, narrowly lanceolate to oblanceolate, sometimes foliaceous bractlets or bracts 10-30(-60) mm, margins entire, usually ciliate, abaxial faces usually glabrous. Involucres narrowly campanulate to cylindric, 9-16 × 5-8(-12) mm. Phyllaries 4-8+, ± oblong, 9-16 mm. Ray florets usually 0, sometimes 3-5+; laminae yellowish, 2-10 mm. Disc florets 6-20(-30+); corollas yellowish, 3-6 mm. Cypselae red-brown, flattened, sometimes weakly 4-angled, narrowly cuneate to linear, outer 6-10 mm, inner 8-13 mm, margins evenly antrorsely strigillose, apices truncate, faces smooth or ± striate, ± evenly antrorsely strigillose; pappi of 2(-4) erect to spreading, antrorsely barbed awns (2-)3-9 mm.

Flowering Sep. Borders of streams, estuaries; 0-10+ m; Del., Md., N.J., N.Y., Pa.

Much like no. 6 [Bidens eatonii Fernald]; achenes copiously appressed-hispidulous, narrowly linear-cuneate, 6-13 נ1-1.5 mm, the median ribs obscure or none; awns 2(-4), antrorsely barbed, from a little less than half to usually evidently more than half as long as the achene; 2n=48. Estuaries; N.Y. to Md. July-Oct. (B. mariana)

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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