Perennials, 100-200 cm (rhi-zomatous). Stems erect, hirsute. Leaves cauline; mostly opposite; petioles 0.4-2 cm; blades (3-nerved from bases) lanceolate to ovate, 6.5-18 × 1-8 cm, bases truncate to broadly rounded or cuneate, margins subentire to serrate (flat), abaxial faces ± hirsute, gland-dotted (adaxial not gland-dotted). Heads 1-7. Peduncles 1-5 cm. Involucres hemispheric, 10-25 mm diam. Phyllaries 18-25 (usually loose, spreading, not reflexed), lanceolate, 7-12 × 2.5-3.5 mm, (margins ciliate) apices acute to short-acuminate, abaxial faces not gland-dotted. Paleae 7-10 mm, 3-toothed (apices yellowish, hairy). Ray florets 10-15; laminae 15-20 mm. Disc florets 40+; corollas 5.5-6.5 mm, lobes yellow; anthers dark brown or black, appendages dark or yellowish. Cypselae 4-4.5 mm, glabrate or distally puberulent; pappi of 2 aristate scales 2.5-3.2 mm. 2n = 68. Flowering late summer-fall. Dry, open sites, woodland edges, roadsides; 10-900+ m; Ont.; Ala., Ark., Conn., Del., D.C., Fla., Ga., Ill., Ind., Iowa, Kans., Ky., La., Md., Mich., Minn., Miss., Mo., Nebr., N.Y., N.C., Ohio, Okla., Pa., S.C., Tenn., Tex., Va., W.Va., Wis.; Mexico (Coahuila, Nuevo León). Helianthus hirsutus is distinguished from H. strumosus by hairy stems and usually yellow (as opposed to dark) anther appendages, and from H. divaricatus by petioles and leaf blades 3-nerved distal to bases. Mexican plants of H. hirsutus are sometimes labeled with the synonymous H. leptocaulis (S. Watson) S. F. Blake, and plants from Mexico and the southwestern United States often have leaf bases cuneate rather than truncate.
Fibrous-rooted perennial from long rhizomes; stems 0.6-2 m, spreading-hairy; lvs all or mostly opposite, generally ascending on a short petiole 5-15(-20) mm, hirsute on both sides or scabrous above, narrowly lanceolate to ovate, 7-16 נ(1.5-)2-6 cm, serrate to entire, triplinerved at the abruptly contracted to often broadly rounded or subcordate base; heads 1-several on short, stout peduncles; disk yellow, (1.2-)1.5-2(-2.5) cm wide; invol bracts conspicuously ciliate and often also hairy on the back, slender, long-pointed, often with loose or reflexed tip; rays 10-15, 1.5-3.5 cm; 2n=68. Dry, wooded or open places; Pa. to Minn., s. to n. Fla. and Tex. July-Oct. (H. chartaceus)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.