Roots extend several feet deep and some distance horizontally. Leaves usually with crinkled edges and spiny margins, somewhat lobed, and smooth. Flower heads numerous, compact, about three-fourths of an inch or less in diameter, of lavender disk flowers only. Surrounded by bracts without spiny tips. Male and female flowers usually contained in separate heads and borne on different plants.
Seed is attached to tannish down that is easily broken off.
There is also a Bull Thistle that is very similar except it is a biennial, reproduces only from seed, has a larger bloom, and the seed is straw-colored, striped with brown. Taproot large, deep, and fleshy. Stem is erect, branched, smooth, and with a milky sap. Leaves are basal and along the stems. Leaves on stems are smaller and either less lobed or entire.