An erect, biennial, prickly herb, with spiny leaves and smooth stem, 3 to 8 feet high, slender, leafy, striate and branching above. When young the stem is woolly or hairy, becoming smooth when older. Leaves when young, densely white tomentose on the under surface, becoming glabrous when mature and then green on both sides, or somewhat hairy on the upper surface, deeply pinnatifid into lanceolate or oblong, toothed, spiny segments tipped with slender prickles. Basal leaves petioled, 4 to 8 inches long, upper leaves sessile and smaller. Inflorescence consisting of a solitary or several large terminal heads of flowers, about 11/2 inches broad and as high, on naked peduncles or the peduncles with a few small, bractlike leaves. Flowers all tubular, and purple in color. Involucre of the heads glutinous and webby, composed of closely appressed bracts, the outer ones ovate or ovate-lanceolate, the inner linear-lanceolate, pointed and all of them unarmed or without prickles.
Common in swamps and moist soil, Newfoundland to Saskatchewan, south to Florida and Texas. Flowering from July to October.
Memoir 15 N. Y. State Museum
Swamp Thistle - Cirsium mutcum