Cirsium horridulum var. megacanthum
Sida 21: 214. 2004. 2004
Plants 100–250 cm. Stems glabrous to sparsely tomentose. Leaves: blades oblanceolate or oblong-elliptic, 20–40 cm, shallowly to deeply pinnatifid, main spines 10–30 mm, abaxial faces glabrous or nearly so. Heads 10–20. Involucres 4–5 × 5–8 cm, glabrous. Phyllaries: outer and middle bodies scabridulous or minutely spinulose, marginal spinules usually 1 mm or shorter. Corollas pink to purple. 2n = 32, 34.
Phenology: Flowering spring (Mar–Jun).
Habitat: Meadows, pastures, roadsides, forest openings, low ground, often in damp soil
Elevation: 0–100 m
Ala., Ark., Fla., La., Miss., Okla., Tex.
Variety megacanthum occurs on the coastal plain and lower piedmont from northern Florida to eastern Texas and southeastern Oklahoma. Nuttall described this thistle as “one of the most terribly armed plants in the genus.”