Musk thistle

Musk thistle - Carduus nutans L.

Family: Asteraceae (Composite family)
Life cycle: Biennial
Native status: Introduced as an ornamental for its showy flowers
Habitat: Pastures, roadsides,

General description: First-year plants form a basal rosette up to 2 ft wide; leaves are deeply lobed with spine-tipped margins. In the second year flower stalk elongates up to 5 ft tall; numerous pink to purple flower heads up to 2 in wide, the largest of Iowa’s thistles; the head is surrounded by sharp bracts. The base of the flower heads is flatter than that of the bull or Canada thistle.

Key ID traits: Margins of leaves often silverish, giving them a frosted appearance. On flowering plants, the base of the leaf extends down the stem, forming spiny wings. Few hairs on leaves

Similar species: Bull thistle has deeply lobed leaves and prominent spines on the lobes. Canada thistle is much smaller, and the leaves are not as deeply lobed. Field thistle is a native plant with few hairs on the upper leaf surface, but the lower surface is densely covered with white hairs. Field thistle flowers much later in the season than musk and other thistles.

Miscellaneous: A small percentage of musk thistle plants act as annuals; these plants flower later in the summer and are much shorter than two-year-old plants. Musk thistle was introduced to North America as a garden flower by European colonists. The musk thistle weevil was introduced as a biological control agent in the 1980’s and is common across the state. Its larvae feed on developing seedsthe  within the flower head.