Perennials, 30-100 cm. Stems usually 1, usually branched distally, strongly winged, glabrous or sparsely hairy proximally, sparsely to moderately hairy distally. Leaves glabrous or sparsely to moderately hairy; basal blades oblanceolate to obovate or spatulate, entire or serrate; proximal and mid blades oblanceolate to lanceolate, entire or toothed; distal blades lanceolate to lance-linear, entire. Heads (1-)5-50(-80+) per plant, in paniculiform arrays. Peduncles 3-10 cm, sparsely to moderately hairy. Involucres globoid to usually ovoid, 8-17 × 9-17 mm. Phyllaries (connate proximally) moderately to densely hairy. Ray florets usually 8-13, neuter, sometimes 0; corollas yellow to reddish brown to red to purple, 10-20 × 5-10 mm. Disc florets 250-500(-700+); corollas yellow proximally and purple distally or purple throughout, 2.3-3.7 mm, lobes 4(-5). Cypselae 1-1.2 mm, moderately hairy; pappi of 5-6 entire, aristate scales 0.6-1(-1.7) mm. 2n = 28. Flowering (Apr-)May-Jul(-Oct). Ditches, fields, washes, along streams; 10-900 m; N.S., Ont., Que.; Ala., Ark., Fla., Ga., Ill., Ind., Ky., La., Md., Mass., Mich., Miss., Mo., N.J., N.C., Ohio, Okla., Pa., S.C., Tenn., Tex., Va., W.Va., Wis. It has been suggested that Helenium flexuosum may be of hybrid origin from H. campestre (perennial, 2n = 28) and some member of Helenium sect. Tetrodus (H. F. L. Rock 1957). The only member of sect. Tetrodus that has a chromosome number of 2n = 28 is H. linifolium, an annual from southern Texas.
Fibrous-rooted perennial 2-10 dm, ±puberulent or villous- puberulent at least on the stem, the lower part of the stem generally spreading-villous; lvs decurrent but smaller, fewer, and more erect than in no. 1 [Helenium autumnale L.], entire or subentire, the lowermost ones oblanceolate, commonly deciduous, the others oblong or lanceolate to lance-linear, sessile, generally not much reduced upwards, 3-12 נ0.5-2 cm; heads in well developed plants numerous in an open, corymbiform, leafy-bracteate infl, the disk subglobose or ovoid-globose, 6-15 mm wide, red-brown or purplish; rays ca 8 to ca 13, neutral, sometimes purplish at base, (0.5-)1-2 cm (rarely wanting); disk-fls predominantly 4-merous; pappus- scales 5(-8), ovate or lanceolate, shortly awn-tipped, ca (0.5-)1 mm overall; 2n=28. Moist ground and waste places; Mass. and N.H. to Fla., w. to Wis., Ill., Mo. and Tex., apparently only intr. northward. June-Oct. (H. nudiflorum; H. polyphyllum)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.