Sp. Pl. 2: 905. 1753.
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.
Phenology: Flowering late summer–fall.
Habitat: Woods, roadsides, prairies
Elevation: 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.