Annuals or perennials, 10-160 cm. Stems 1(-10), erect, simple or branched distally (usually ± winged by decurrent leaf bases), glabrous or sparsely to densely hairy. Leaves usually mostly cauline; mostly alternate (proximal sometimes opposite); petiolate or sessile; blades mostly elliptic, lanceolate, linear, oblanceolate, oblong, ovate, or spatulate, often pinnately lobed or pinnatifid, ultimate margins entire or toothed, faces glabrous or sparsely to densely hairy, gland-dotted. Heads radiate or discoid, borne singly or (2-300+) in paniculiform to corymbiform arrays. Involucres ± globose, hemispheric, obconic, or ovoid, 4-34 mm diam. Phyllaries persistent, 9-34(-40+) in (1-)2[-3] series (distinct or proximally connate, usually reflexed in fruit, glabrous or sparsely to densely hairy, gland-dotted). Receptacles conic, ± globose, hemispheric, or ovoid, pitted (glabrous), epaleate (rarely bearing setiform enations). Ray florets 0 or 7-34, pistillate and fertile or neuter; corollas yellow, yellow with purple streaks, reddish brown to red proximally and yellow distally, or reddish brown to red or purple throughout. Disc florets 75-1000+, bisexual, fertile; corollas yellow, purple, or yellow to yellow-green proximally and yellow-brown, brown or reddish brown to purple distally, tubes shorter than throats, lobes 4 or 5, ± deltate (style-branch apices penicillate or truncate). Cypselae mostly obpyramidal, 4-5-angled, glabrous or sparsely to densely hairy; pappi persistent, of 5-12 entire or ± lacerate, sometimes aristate scales. x = 17. Helenium polyphyllum Small is apparently a hybrid between H. autumnale and H. flexuosum.
Heads mostly radiate, the rays pistillate or neutral, mostly yellow, cuneate, 3-lobed, not very numerous; invol bracts in 2-3 series, subequal or the inner shorter, ±herbaceous, generally soon deflexed, the outer sometimes joined at the base; receptacle convex to ovoid or conic, naked; disk-fls very numerous, perfect, the cor-lobes glandular-hairy; style branches flattened, with ventromarginal stigmatic lines and dilated, subtruncate, penicillate tip; achenes 4-5-angled, with as many intermediate ribs, pubescent on the angles and ribs, or glabrous; pappus of 5-10 scarious or hyaline, often awn-tipped scales; herbs with alternate, glandular-punctate, usually decurrent lvs and solitary to numerous heads. 40, New World.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.