Eastern Forest Threat Center - Musk Thistle

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Musk thistle flower and seeds

Musk thistle flower and seeds

Steve Dewey, Utah State University, Bugwood.org

Musk Thistle
Carduus nutans

Musk thistle, a native of western Europe, was introduced into the U.S. in the early 1800s. It has a long history as a rangeland pest in the U.S.

Keywords: Asteraceae, biennial, herb, spiny stems and leaves, disk-shaped flower heads, drooping flower heads, bristled seeds; Common names: nodding thistle

Distribution Map Distribution Source Image

Threat Description

Musk thistle is an aggressive, biennial herb with multi-branched stems and painful spiny stems and leaves. Mature plants range in height from 1½ to 6 ft. Leaves are dark green and coarsely lobed with a smooth waxy surface and a yellowish to white spine at the tip. Flowers emerge in early May to August. The large disk-shaped flower heads, containing hundreds of tiny individual red-purple flowers, are 1½ to 3½ in. in length and occur at the tips of stems. Flower heads droop to a 90-degree angle from the stem when mature, hence the plant’s alternate name, nodding thistle. Seed dissemination occurs approximately one month after the flowers form. Seeds are straw-colored and adorned with plume-like bristles. A single flower head may produce 1,200 seeds and a single plant up to 120,000 seeds that may be wind blown for miles. Seed may remain viable in the soil for over ten years. Musk thistle grows in neutral to acidic soils from sea level to about 8,000 ft. elevation. It invades open natural areas such as meadows, prairies, and grassy balds. It spreads rapidly in areas subjected to frequent natural disturbance events, but does not grow well in excessively wet, dry, or shady conditions.