Biennial thistle with the upper stems and branches winged with a wavy, prickly tissue. Flowerheads typical of thistles, reddish purple to purple, with a prominent involucre (the flowerhead base, covered by leaflike bracts), which is covered with a fine, cobweb-like silk. Spiny bracts grow right up to the flowerheads; the middle and lower spines are spreading and yellow or straw-colored. Blooms June-September. Leaves alternate, deeply lobed, hairy, spiny, the upper surface with stiff bristles.
Similar species: There are nine species of Cirsium in Missouri. Bull thistle and Platte thistle (C. canescens) are the only two with stems having spiny-margined wings. Platte thistle has cream-colored flowers (rarely pale pink). It has been collected only once in Missouri, along a railroad in Jackson County in 1951.