Perennials, 50-200 cm (rhizomatous). Stems erect, scabro-hispid. Leaves mostly basal; opposite, or opposite (proximal) and alternate; petioles 0-1 cm; blades lance-ovate to oblong-lanceolate, or rhombic-ovate to lance-linear, 5-27 × 2-6 cm, bases cuneate, margins serrate to subentire, abaxial faces sparsely hispid, sparsely, if at all, gland-dotted (cauline smaller). Heads 1-10. Peduncles 3-12 cm. Involucres hemispheric, 15-23 mm diam. Phyllaries 25-35, ovate, 6-10 × 3-5 mm, (margins ciliate) apices acute, abaxial faces glabrate to hispid. Paleae 9-10 mm, shallowly 3-toothed to subentire (apices ciliate, hairy). Ray florets 10-20; laminae 20-35 mm (abaxial faces usually gland-dotted). Disc florets 75+; corollas 6.5-7 mm, lobes usually reddish, sometimes yellow ; anthers dark, appendages dark (style branches yellow). Cypselae 5-6 mm, glabrate; pappi of 2 aristate scales 4.5-5 mm plus 1-4 smaller aristate scales 0.3-2 mm. 2n = 102 (subspecies unknown). Variation within Helianthus pauciflorus is complex and is complicated by hybridization with H. tuberosus. Hybrids with H. tuberosus are known as H. ×laetiflorus, which is frequently cultivated.
Perennial with long rhizomes; stems scabrous or hispid to subglabrous, ±naked above, the heads long-pedunculate; lvs nearly all opposite, to 15 pairs below the infl, scabrous to shortly hispid on both sides, mostly (2-)2.5-8 times as long as wide, mostly trinerved, toothed or entire, tapering to a short petiole or petiolar base, the middle ones seldom much smaller than the lowest ones present at anthesis; disk red-purple, 1.5-2.5(-3) cm wide; invol bracts evidently imbricate, broad, firm, appressed, mostly ovate or broadly lanceolate, sharply acute to obtuse, conspicuously ciliolate, otherwise generally glabrous; rays 10-21, 1.5-3(-3.5) cm; pappus nearly always with some short scales in addition to the 2 longer awns; 2n=102. Prairies and roadsides; Mich. and Ind. to Alta., N.M., and Tex., and e. occasionally to Mass. and N.B. Aug., Sept. Two vars.:
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.