A weedy perennial forb with wide-spreading, horizontal, fibrous roots that can be 3 feet deep. The grooved, slender stems branch only at the top and are slightly hairy when young, becoming covered with hair as the plant grows. The oblong, tapering, stalkless leaves are deeply divided, with prickly margins. Leaves are green on both sides with a smooth or slightly downy lower surface. Blooms June through September. Flowers are rose-purple or white, and are smaller (3/4 inch in diameter) and more numerous than for many other thistles. The flower heads are compact and appear on upper stems. Some plants have only female flowers; others have both male and combination (perfect) flowers. Seeds are small (3/16 inch long), light brown, smooth and slightly tapered, with a tuft of tan hair loosely attached to the tip.
Similar species: Nine species of Cirsium have been recorded for our state. Some are native and uncommon. The three exotic invasive thistles all have leaves that are typically green on both sides, while leaves of natives usually have whitened and woolly undersides. Exotic thistles also tend to have heavily branched stems and more numerous flower heads per stem. Our native thistles are valuable members of our flora, providing food, habitat, and/or nesting materials for monarchs, goldfinches, and more.