Annuals (biennials), 30-100+ cm. Leaves: petioles 5-30 mm; blades ± deltate to ovate overall, 40-80(-150+) × 25-50(-80+) mm, usually laciniately 1-pinnatisect, ultimate lobes 3(-7), lanceolate to linear, 25-60(-120+) × (3-)6-20(-25) mm, bases cuneate, ultimate margins incised, dentate, or serrate, ciliate, apices acute to attenuate, faces glabrous or hirtellous to scabrellous. Heads borne singly or in 2s or 3s or in open, ± corymbiform arrays. Peduncles 10-20(-50) mm. Calyculi of 12-21+ spreading to reflexed, linear, seldom foliaceous bractlets (6-)8-12(-20+) mm, margins coarsely ciliate, abaxial faces glabrous or scabrellous. Involucres turbinate to hemispheric, 4-5 × 6-10 mm. Phyllaries 6-8+, lance-ovate to lanceolate, 4-7 mm. Ray florets 8; laminae golden yellow, 10-25+ mm. Disc florets (40-)60-100+; corollas yellow, 2.5-3 mm. Cypselae blackish or brown to yellowish, ± flattened, obovate or oblanceolate to cuneate, outer 5-7 mm, inner 7-8 mm (lengths mostly 1.5-2.5 widths), margins (± corky-winged) antrorsely barbed or ciliate, apices ± truncate, faces glabrous or strigillose, sometimes tuberculate; pappi 0, or of 2 divergent, retrorsely barbed awns or ± deltate scales 0.1-0.5(-1.5) mm. 2n = 24. Flowering Aug-Oct. Marshes, bogs, flood plains, disturbed sites; 10-1500 m; Ont.; Ala., Ark., Colo., Ill., Ind., Iowa, Kans., La., Md., Mich., Mo., Nebr., N.J., N.Mex., N.C., Okla., Pa., S.C., Tenn., Tex., Va.
From Flora of Indiana (1940) by Charles C. Deam
In 1921, I collected this form in Owen County along the roadside about a half mile north of Coal City, and in 1932, I found large colonies of it along the roadside just south of Coal City. It grew in hard, white, clay soil and, no doubt, it has a wider distribution than our collections indicate.
Indiana Coefficient of Conservatism: C = 1
Wetland Indicator Status: FACW
Diagnostic Traits: Very similar to B. aristosa and perhaps only a variation of that taxon. Bidens polylepis , according to FNA, generally has 12-21 calyculi that are longer than the phyllaries and are coarsely ciliate. Those of B. aristosa are fewer, shorter, and less strongly ciliate.
Much like no. 14 [Bidens aristosa (Michx.) Britton], but the outer invol bracts mostly 12-25(-30), 10-25 mm, mostly surpassing the inner, somewhat curled and twisted, conspicuously hispid-ciliate and often also coarsely short-hairy on the back; pappus more commonly short or obsolete; 2n=24. Wet places, mostly in sun; Ozark, plains, and prairie sp., n. to Neb., Io., Ill., and Ind., and adventive eastward. Aug.-Oct. (B. involucrata, a preoccupied name)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.