Annuals, 10-100 cm. Stems 1-3(-15), usually branched distally, not winged, glabrous or sparsely hairy. Leaves glabrous or sparsely hairy; basal blades linear to ovate, entire or pinnately toothed or lobed to pinnatifid; mid and distal blades linear, entire. Heads (1-)10-150(-250+) per plant, in paniculiform arrays. Peduncles 3-11 cm, sparsely hairy. Involucres hemispheric to globose or globoid, 5-9 × 6-10 mm. Phyllaries moderately to densely hairy. Ray florets 8-10, pistillate, fertile; corollas yellow, 4.5-14 × 2-10 mm. Disc florets 75-250+; corollas yellow proximally, yellow to yellow-brown or purple distally, 1.6-2.7 × 0.8-1.2 mm, lobes 5. Cypselae 0.7-1.3 mm, moderately to densely hairy; pappi of 6-8 entire, aristate scales 1-1.8 mm.
Taprooted, glabrous or atomiferous-glandular annual 2-5 dm; lvs very numerous, linear or linear-filiform, 1.5-8 cm, seldom over 2 mm wide; heads on short, naked peduncles extending above the leafy part of the plant; rays 5-10, pistillate, 5-12 mm; disk subglobose, yellow, 6-12 mm wide; pappus-scales commonly 6-8, ca 1.5 mm, the awn-tip about equaling the hyaline body; 2n=30. Prairies, open woods, fields, and waste places, especially in sandy soil; mainly Texan and Ozarkian, n. to Mo., but irregularly intr. e. to Conn., Md., Va., Ga., and Fla., and in Mex. and W.I. June-Oct. (H. tenuifolium) We have only the var. amarum, with yellow disk and entire lvs.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.