10. Onopordum Linnaeus, Sp. Pl. 2: 827. 1753; Gen. Pl. ed. 5, 359. 1754.
Cotton thistle, onoporde [Greek onopordon, name for cotton thistle]
David J. Keil
Biennials, 50–400+ cm, coarse, prickly. Stems usually erect, ± branched, spiny-winged. Leaves basal and cauline; winged-petiolate (basal) or sessile (cauline); blade bases narrowing. margins pinnately lobed or divided and dentate, teeth and lobes tipped with stout spines. Heads discoid, borne singly or in corymbiform arrays; (peduncles 0 or spiny winged). Involucres hemispheric to ovoid or spheric. Phyllaries many in 8–10+ series. linear to ovate, entire, tapered to stiff spines, middle and outer often spreading or reflexed. Receptacles flat to convex, epaleate, not bristly, alveolate with apically fringed pits. Florets many; corollas white or purple, actinomorphic or weakly zygmorphic, tubes slender, throats cylindric or narrowly goblet-shaped. lobes linear; anther bases acute-tailed, apical appendages subulate; style branches: fused portions with minutely hairy nodes, long, cylindric, minutely papillate, distinct portions minute. Cypselae ± cylindric, 4–5-angled, usually ± transversely roughened, glabrous, attachment scars basal; pappi falling in ring, of many barbed or plumose bristles, basally connate. x = 17.
Species 25–60 (3 in the flora): introduced; Eurasia.
Dress, W. J. 1966. Notes on the cultivated Compositae 9. Onopordum. Baileya 14: 74–86.