Cirsium horridulum

Biennials or perennials, (± fleshy), 15-250 cm; stout taproots and a fascicle of fleshy lateral roots, often perennating by root sprouts. Stems 1-several, usually erect, often stout, glabrous to densely tomentose; branches 0-many, spreading to ascending, short, stout. Leaves: blades linear to oblanceolate or oblong-elliptic, 10-40 × 2-10 cm, unlobed and spiny-dentate to deeply pinnatifid, lobes spiny-dentate or coarsely lobed, main spines stout, 5-30 mm, abaxial faces subglabrous to loosely tomentose, adaxial glabrous to ± densely villous with septate trichomes; basal present at flowering, spiny winged-petiolate, bases often tapered; principal cauline sessile, well distributed, often not much reduced distally, bases often ± auriculate-clasping; distal cauline often spinier than the proximal. Heads 1-20 in subcapitate to corymbiform arrays (each closely subtended by an involucre-like ring of spiny-margined bracts). Peduncles 0-5 cm. Involucres hemispheric to campanulate, 3-5 × 3-8 cm. Phyllaries in 5-9 series, subequal to imbricate, light green to stramineous, lanceolate to linear, distally often with reddish margins, abaxial faces without glutinous ridge, often ± thinly tomentose, often scabridulous in submarginal bands; outer and middle appressed-ascending, bodies usually reddish-tinged, margins setulose-ciliolate, apices acuminate, spines 1-2 mm, weak; apices of inner straight, flat. Corollas white to yellow, pink, purple, or red, 30-47 mm, tubes 11-30 mm, throats 6-10 mm, lobes 7-10 mm; style tips 3-5 mm. Cypselae straw-colored to tan, 4-6 mm, apical collars weakly differentiated; pappi 25-35 mm. 2n = 32, 33, 34, 35.

Although several variants have been given taxonomic recognition as species, these seem at most races. Flower color varies greatly, sometimes within populations and sometimes on a populational or regional basis. Herbarium specimens are sometimes difficult to assign to variety.

Stout biennial 2-15 dm, simple or with short, stout, ascending, peduncle-like branches, some of the roots commonly fleshy-thickened; herbage thinly tomentose and eventually generally glabrate, or the lvs merely arachnoid and glabrate; lvs strongly spiny, broad and pinnatifid to seldom narrow and merely spiny-toothed, the largest ones at or near the base; heads light yellow or white to lavender or purple, several or solitary, each subtended by a number of narrow, erect, strongly spiny, reduced lvs; invol (2.5-)3-5 cm, the outer bracts with erect spine-tip, the inner merely attenuate, all with modified, shortly scabrous or scabrous-ciliate margin; achenes 4-6 mm; 2n=32, 34. Open places, especially in sandy soil or along salt or fresh marshes; coastal states (and Pa.) from Me. to Fla. and Tex.; Mex. May-Aug. (C. spinosissimum) Ours are the widespread var. horridulum.

Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.

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