Perennials, 100-200 cm, herbage usually ± tomentose, spiny. Stems usually erect, simple or branched. Leaves basal and cauline; sessile or petiolate; blade margins dentate to pinnately 1-3-pinnately lobed or divided, lobes and teeth spiny, faces ± tomentose, sometimes glandular. Heads discoid, many, each with 1 floret, sessile, in pedunculate, spheric secondary heads. Secondary involucres of reflexed, laciniate-pinnatifid bracts. Primary involucres ellipsoid, subtended by bristles. Phyllaries many in several series, unequal, lanceolate (outer) to linear (inner), entire, apices sometimes expanded and fringed, not spine-tipped. Receptacles turbinate, bearing elongate subulate scales . Florets 1 per primary head; corollas white to greenish, blue-gray, blue, or purple, tubes elongate, throats very short, lobes linear; anther bases sharply tailed, apical appendages narrowly triangular, acute; style branches: fused portions with minutely hairy rings, distinct portions divergent, linear-oblong. Cypselae ± cylindric, 4-angled, apices ± truncate, without crowns, densely villous with long, stiff, appressed or ascending, multicellular hairs, attachment scars basal; pappi of many, short. ± connate [or distinct] scales. x = 13, 14, 15, 16.
Heads 1-fld, numerous, closely aggregated into globose secondary heads that often have a common invol of a few narrow, reflexed bracts; proper invol subtended by a tuft of capillary bristles, narrow, its bracts well imbricate, firm, often awn- tipped; fls tubular and perfect, the cor blue to purple or white, with slender tube and long, narrow lobes; anthers with a firm, narrow terminal appendage, shortly tailed at the base, the tails fringed-hairy; style with a ring of hairs and an abrupt change of texture below the rather short, papillate branches; achenes fusiform, hairy; pappus of numerous short setae or narrow scales, these distinct or ±united, forming a crown; spiny perennial thistles, generally ±white- tomentose, with alternate, toothed or pinnatifid lvs. 100, Old World.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.