24. Bidens eatonii Fernald, Rhodora. 5: 92, plate 45, figs. 11–14. 1903.
Bidens eatonii var. fallax Fernald; B. eatonii var. illicita S. F. Blake; B. eatonii var. interstes (Fassett) Fassett; B. eatonii var. kennebecensis Fernald; B. eatonii var. major Fassett; B. eatonii var. mutabilis Fassett; B. eatonii var. simulans Fassett
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.