Annuals, (15-)30-50(-150) cm. Leaves: petioles 10-50 mm; blades ± deltate to ovate overall, 50-100(-150+) × (15-)30-80(-120+) mm, usually laciniately 1-pinnatisect or 3-5-foliolate, primary lobes or leaflets ± lanceolate, 20-80(-120) × 10-25(-40+) mm, blades rarely 2-3-pinnatisect, bases cuneate, ultimate margins dentate to serrate, little, if at all, ciliate, apices acute to attenuate, faces glabrous or ± hispidulous. Heads borne singly or in 2s or 3s or in open, corymbiform arrays, erect. Peduncles (10-)40-150+ mm. Calyculi of 10-16(-21) ascending to spreading, spatulate to linear, seldom foliaceous bractlets or bracts 10-20(-40) mm, margins usually hispid-ciliate, abaxial faces ± hispidulous. Involucres hemispheric or broader, 5-6 × 8-10 mm. Phyllaries 10-12, ovate to lanceolate, 6-9 mm. Ray florets 0 or 3-5+; laminae pale yellow, 2.5-3.5 mm. Disc florets 40-60(-150+); corollas yellow, 2.5-3.5 mm. Cypselae purplish, brown, olive, or stramineous, ± flattened, obovate to cuneate, outer 6-10 mm, inner 8-12 mm, margins (sometime ± winged) proximally antrorsely, distally retrorsely barbed, apices ± truncate, faces obscurely 1-nerved, sometimes tuberculate, glabrous or sparsely strigillose; pappi of 2 erect to divergent, retrorsely barbed awns 3-4(-7) mm. 2n = 24, 48. Flowering Aug-Sep(-Oct). Ditches, shores of lakes and streams, swamps, marshes, moist woods, roadsides, railroads, fields, waste areas; 10-1000 m; Alta., B.C., Man., N.B., N.S., Ont., Que., Sask.; Ark., Calif., Colo., Conn., Del., D.C., Ga., Idaho, Ill., Ind., Iowa, Kans., Ky., Maine, Md., Mass., Mich., Minn., Miss., Mo., Mont., Nebr., Nev., N.H., N.J., N.Y., N.C., N.Dak., Ohio, Okla., Oreg., Pa., R.I., S.C., S.Dak., Tenn., Vt., Va., Wash., W.Va., Wis., Wyo.; introduced in Europe. Bidens vulgata is similar to B. frondosa; it is more robust. Both are phenotypically plastic. Locally, B. vulgata often matures earlier than B. frondosa.
From Flora of Indiana (1940) by Charles C. Deam
Frequent to common in all parts of the state although there are no records from the dune area. It is found usually in a moist habitat in woodland, stubble and fallow fields, and waste places and along roadsides. This species varies greatly in the density and harshness of its pubescence. The var. puberula (Wieg.) Greene has been reported from Indiana but I am now referring these reports to the species.
Much like no. 9 [Bidens frondosa L.], averaging a little more robust and larger- headed, the herbage glabrous to densely villous-puberulent; outer invol bracts in well developed heads 10-16(-21), typically 13, averaging a little more leafy; disk yellow; anthers mostly included; achenes to 12 mm, dark as in no. 9, or more commonly olivaceous or somewhat yellowish; 2n=24, 48. Wet to dryish waste places; widespread in n. U.S. and adj. Can., s. to N.C., Mo., and Calif. Aug.-Oct. (B. puberula)
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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