Bull thistle is a clumping biennial that forms a thick taproot in its first growing season. The leaves of bull thistle are covered with soft hairs and needle-like spines on the margin. Leaves of seedlings are not deeply lobed like mature leaves. This is the thistle you stepped on in your bare feet as a kid. Bull thistle will form an erect branched habit in its second season on which the large purple blossoms will form if left unmowed.