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.
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Much like no. 6 [Bidens eatonii Fernald]; achenes copiously appressed-hispidulous, narrowly linear-cuneate, 6–13 × 1–1.5 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)
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