The leaves are of two types. One type forms basal rosettes during the first year, which overwinter, staying green, and killing any plants underneath. The upright flowering stalk grows during the second year, producing smaller, very spiny leaves.
Stems are commonly winged with spiny leaf tissue.
Musk thistle resembles several other thistles that are found in Missouri. Musk thistle has unbranched bristles whereas the thistles in the genus Cirsium have feathery or plume-like bristles. The thistles in the genus Cirsium also tend to have smaller flower heads than does musk thistle. Biennial species like musk thistle die after flowering and therefore do not usually occur in dense colonies. Musk thistle should be accurately identified before attempting any control measures.