11a. Cirsium horridulum Michaux var. horridulum
Carduus spinosissimus Walter 1788, not Cirsium spinosissimum (Linnaeus) Scopoli 1772; C. horridulum var. elliottii Torrey & A. Gray
Plants 15–180 cm. Stems densely tomentose. Leaves: blades oblanceolate or oblong-elliptic, 10–30 cm, shallowly to deeply pinnatifid, main spines mostly 5–10 mm, abaxial faces loosely tomentose. Heads 1–10. Involucres 4–5 × 5–7 cm, ± densely tomentose. Phyllaries: outer and middle bodies scabridulous or minutely spinulose, marginal spinules usually 1 mm or shorter. Corollas yellow or crimson to red-purple. 2n = 32, 34.
Flowering winter–spring (Apr–Jun). Fields, meadows, pinelands, roadsides, often weedy, often in damp soil; 0–300 m; Ala., Conn., Del., Fla., Ga., La., Maine, Md., Mass., Miss., N.H, N.J., N.Y., N.C., Pa., R.I., S.C., Tenn., Tex., Va.
Variety horridulum occurs on the Atlantic and Gulf coastal plains fom southern Maine to Florida and west to eastern Texas and into the piedmont in much of the southeastern United States. Artificial hybrids have been produced between var. horridulum and Cirsium repandum (R. J. Moore and C. Frankton 1969), and natural hybrids with C. pumilum var. pumilum have been reported.