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Musk Thistle

(Carduus nutans L.)

Musk Thistle Flower


Musk thistle was introduced into the United States from Europe. This plant is considered a noxious weed and is included on the Colorado and the Adams County Noxious Weed Lists. Musk thistle is a biennial, which means its first year of growth is a rosette from a stout, corky taproot. Rosettes can appear in either spring or fall. During the second year, the stem bolts and can grow 2 to 6 feet tall. Musk thistle has waxy, spiny leaves. These spines can cause physical harm to wildlife and humans. Leaves are 3 to 6 inches long and are dark green in color with a prominent midrib.

Musk thistle produces many flowers; one plant may produce 100 or more flowerheads. The nodding flowers are large, 1-1/2 to 2-1/2 inches wide, purple, and surrounded by numerous lance-shaped, spine-tipped bracts. Flowering occurs between late May and early June and set seed in late June/early July.

Musk thistle is usually found as a single plant rather than in dense colonies like Canada thistle and leafy spurge. Musk thistle is found in many county locations such as rangeland, riparian areas, and ditch bank sites. If you think you have this weed on your property, or would like more information, please contact the Adams County Weed Department at 303-637-8115.


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