musk thistle

Carduus nutans L.

U.S. Nativity: Exotic
Habit: Herb

Synonym(s): nodding plumeless thistle, nodding thistle, bristle thistle

Carduus nutans is an herbaceous, biennial plant that grows to 6 ft. (1.8 m) tall. The stem has very spiny wings. Carduus species may hybridize with each other.
Leaves are green and lanceolate to oblong-lanceolate. They are often pinnatifid and are very prickly. Leaves are usually sessile to slightly clasping. Basal leaves are 4-16 in. (10-40 cm) long. Leaf characteristics are variable across different varieties and subspecies.
Showy, solitary, hemispherical, red to purple, disk flowers bloom from June to September. Phyllaries are spinetipped and overlap with several rows.
Fruits are small achenes, 1.52 in. (45 mm) long, about 0.04 in. (1 mm) in diameter, including a white to light brown pappus. The seeds have longitudinal dotted stripes.
Ecological Threat
Carduus nutans invades a variety of disturbed areas. Pastures are particularly at risk because It is unpalatable to livestock. Once established it can spread rapidly due to high seed production (as much as 120,000 seed per plant). Carduus nutans is native to Western Europe and was accidentally introduced into the United States in the early 1900s.

Identification, Biology, Control and Management Resources

Biological Control of Invasive Plants in the Eastern United States - USDA Forest Service
Southeast Exotic Pest Plant Council Invasive Plant Manual - SE-EPPC
Fire Effects Information System - USDA Forest Service
Weeds Gone Wild: Alien Plant Invaders of Natural Areas - Plant Conservation Alliance
Element Stewardship Abstract - The Nature Conservancy
Weed of the Week - USDA Forest Service
Weed Field Guides - USDA Forest Service