Perennials, 100-200 cm (rhizomatous). Stems erect, glabrous or glabrate. Leaves cauline; mostly opposite, sometimes alternate (distal); petioles 1-3 cm; blades (light to dark green, 3-nerved distal to bases) lanceolate to lance-ovate or ovate, 7-18 × 2-10 cm, bases subcordate to ± cuneate, margins entire to ± serrate, abaxial faces glabrous or tomentulose, usually densely gland-dotted. Heads 3-15. Peduncles 1-9 cm. Involucres cylindric to hemispheric, 8-20 mm diam. Phyllaries 18-25 (erect, loose, or squarrose), lanceolate, 5.5-10 × 1.5-3 mm (equaling or slightly surpassing discs), (margins usually ciliate) apices acute to acuminate, abaxial faces glabrous or hispidulous, usually not gland-dotted. Paleae 5.3-6.5 mm, 3-toothed. Ray florets 10-20; laminae ca. 12-20(-30) mm. Disc florets 35+; corollas 5.5-6.5 mm, lobes yellow; anthers dark, appendages dark or reddish brown. Cypselae 4-5.5 mm, glabrate; pappi of 2 aristate scales (1-)2-2.5 mm. 2n = 68, 102. Flowering late summer-fall. Woods , roadsides, prairies; 0-1500 m; Ont., Que.; Ala., Ark., Conn., Del., D.C., Fla., Ga., Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., N.H., N.J., N.Y., N.C., N.Dak., Ohio, Okla., Pa., R.I., S.C., Tenn., Tex., Vt., Va., W.Va., Wis. Helianthus strumosus is variable, particularly for leaf shape and indument; sufficient study has not been undertaken to evaluate whether regional forms deserve taxonomic recognition. Hybridization with other polyploids, including H. decapetalus, H. hirsutus, and H. tuberosus, further complicates the situation. It differs from H. tuberosus in having glabrous (or glabrate) stems and in lacking tubers.
Rhizomatous perennial; stems 1-2 m, glabrous below the infl or with a few long hairs, often glaucous; lvs opposite or the uppermost alternate, relatively thick and firm, scabrous-hispid above, green and moderately short-hairy to more often glaucous and subglabrous beneath, mostly broadly lanceolate to ovate and 8-20 נ2.5-10 cm (sometimes narrower), long-acuminate, shallowly toothed or subentire, commonly decurrent onto the 0.5-3 cm petiole; disk yellow, 1.2-2.5 cm wide; invol bracts subequal, lanceolate, somewhat loose, especially the long-acuminate tips, which commonly equal or slightly surpass the disk; rays 8-15, 1.5-4 cm; 2n=68, 102. Woods and open places; Me. to Fla., w. to Minn., e. Kans., and e. Tex. July-Sept.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
This is a frequent sunflower in the lake area in dry woods and in dry sandy soil along roadsides and elsewhere in a similar soil. South of the lake area it becomes rare, local or absent. Specimens of this species with short petioles and the blades of the leaves nearly round at the base closely approach Helianthus divaricatus. In separating the two species I have relied upon the convergence of the lateral veins of the leaves. In this species they always converge slightly above the base while in Helianthus divaricatus they converge at the base of the blade.