21. Bidens bidentoides (Nuttall) Britton, Bull Torrey Bot. Club. 20: 281. 1893.
Diodonta bidentoides Nuttall, Trans. Amer. Philos. Soc., n. s. 7: 361. 1841; Bidens bidentoides var. mariana (S. F. Blake) Sherff; B. mariana S. F. Blake
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.