Carduus nutans L.
Musk Thistle, Nodding Thistle| Category |
|---|
| Forb/Herb |
|
Similar Species May be confused with the following native and/or non-native species. Landscape Alternatives lists native horticultural substitutes |
Cirsium spp. |
|---|
Description
Height
Thistle stems are commonly 1.5-6 feet (0.5-2.0 m) tall, multi-branched and spiny.Leaves
The dark green leaves are coarsely lobed, elliptic to lanceolate, with a smooth waxy surface, and a yellowish to white spine at the tip. Dimensions average 0.5-1.5 inches (1.5-4.0 cm) wide and 2-5 inches (5-12 cm) long.Flowers
Disk-shaped terminal flowers are 1.5-3.5 inches (4-9 cm) wide and solitary; involucres and corollas are purple; and outer bracts are recurved with spines. Flowers will droop to a 90-degree angle from the stem when large, giving musk thistle its common nickname, nodding thistle.Seeds
Each plant may produce thousands of yellowish-brown or straw-colored seeds with attached feathery bristles.Images
Photo: James H. Miller, USDA Forest Service, Bugwood.orgMore images of Carduus nutans
Life History
Musk thistle is an aggressive biennial plant with large, showy pink flowers on long multi-branched stems. Native to Europe and Asia, it was introduced into the U. S. more than ninety years ago and is declared a noxious weed in many states. It is a member of the Asteraceae (Aster) family.Musk thistle is usually a biennial but may germinate and flower in a single year. Seedlings emerge in mid to late July and develop into a rosette of up to 4 feet (1.2 m) in diameter. Plants overwinter in the rosette stage until they begin to bolt in mid-March. During the bolting stage, plants form multi-branched stems to a height of 6 feet (1.8 m) The number of seed heads per plant is site dependent ranging from 241-561 on favorable sites to 1-18 heads on less favorable sites. Flowers emerge in early May to August and may produce 1200 seeds per head and 120,000 seeds per plant. Seed dissemination occurs approximately one month after the flowers form and seeds may be wind blown for miles. Seeds may remain viable in the soil for over ten years.
Habitat
Establishment of an extensive population of musk thistle is dependent on the availability of light and water. It can grow from sea level to about 8000 feet (2500 m) and in neutral to acidic soil. It spreads rapidly in disturbed areas and is sensitive to competition. Pastureland is particularly vulnerable because the drainage is good, and livestock will avoid thistle due to its spiny leaves and stems. Although musk thistle is infrequently found in dense forests, it can impact natural areas by colonizing areas of natural disturbance such as land slides or areas of frequent flooding. Meadows, prairies, grassy balds, and other open areas are susceptible to invasion.Origin and Distribution
A native of western Europe, musk thistle was introduced into the eastern United States in the early 1900s. It was discovered in Davidson County, Tennessee in 1942 and spread quickly throughout the state. Currently, musk thistle is present in forty states. It is widespread on railroad, highway, and power line rights-of-way, which become a large seed source for invasion of crop and pasture lands as well as open natural areas. Other states where invasive: CO, GA, IA, ID, IL, KS, KY, MD, MN, MO, NC, NE, NJ, OR, PA, SD, VA, WA, WI, WY. Federal or state listed as noxious weed, prohibited, invasive or banned: AR, CA, CO, ID, IL, IA, KS, KY, MD, MN, MO, NE, NV, NM, NC, ND, OH, OK, OR, PA, SD, UT, WA, WV, WY.Sources: Information on this plant page derived primarily from the Tennessee Management Manual.