296. Sclerocarpus Jacquin, Icon. Pl. Rar. 1: 17, plate 176. 1781.
Mexican bone-bract [Greek skleros, hard, and karpos, fruit, alluding to hardened paleae enfolding disc cypselae]
Neil A. Harriman
Annuals [perennials or subshrubs], 60–200 cm. Stems sprawling to erect, branched from bases or ± throughout. Leaves mostly cauline; opposite (proximal) or alternate; petiolate [sessile]; blades 3-nerved, ovate to rhombic or lanceolate, bases cuneate to rounded, margins coarsely toothed, faces glabrous or ± scabrous. Heads radiate, borne singly. Involucres rotate to hemispheric, 12–20 mm diam. Phyllaries persistent, 5–8[–21] in 1(–2) series (green, oblong to linear). Receptacles low-conic, paleate (paleae each closely investing subtended floret, each forming a hard perigynium around a fruit and shed with it). Ray florets 5–8, neuter; corollas (readily falling) yellow to orange. Disc florets 10–50, bisexual, fertile; corollas usually yellow to orange, sometimes with purple, tubes much shorter than cylindric throats, lobes 5, lance-linear. Cypselae (within perigynia) weakly compressed, obliquely obovoid or arcuate (glabrous); pappi 0, or coroniform (of distinct or connate scales or bristles). x = 12.
Species ca. 12 (1 in the flora): s United States, Mexico, Central America; one species in Old World tropics.
Feddema, C. 1966. Systematic Studies in the Genus Sclerocarpus and the Genus Aldama (Compositae). Ph.D. dissertation. University of Michigan.