Eastern Forest Threat Center - Canada Thistle

Search Again

State Information

Select a state,
then click a link.

  • State Forest Agency
  • State Cooperative Extension

County/Parish Information

Select a county,
then click a link.


Canada thistle flowers

Canada thistle flowers

Steve Dewey, Utah State University, Bugwood.org

Canada Thistle
Cirsium arvense

Canada thistle, native to Eurasia, was introduced into the U.S. in the early 1600s. It is considered one of the most tenacious and economically important agricultural weeds, but only in recent years has it been recognized as a problem in natural areas.

Keywords: Asteraceae, herbaceous, perennial, ridged stems, spiny toothed leaf margins, fibrous taproot; Common names: creeping thistle, Californian thistle

Distribution Map Distribution Source Image

Threat Description

Canada thistle is an herbaceous perennial that grows 1½ - 4 ft. tall. Its erect stems are branched, often slightly hairy, and ridged. Leaves are simple, lance-shaped, irregularly lobed with spiny toothed margins, and borne singly and alternately along the stem. Fragrant, rose-purple to lavender or sometimes white flower heads appear from June through October, occurring in rounded, umbrella-shaped clusters. One plant can produce 1,500 to 5,000 seeds that are wind-dispersed and capable of germinating 8 to 10 days after flowers open. Fibrous tap roots may extend 6 ft. deep and have horizontal roots stemming from them to produce new shoots. Canada thistle can be found in clay to gravelly soils and grows in barrens, glades, meadows, prairies, fields, pastures, and waste places. It does best in disturbed upland areas, but also invades wet areas with fluctuating water levels such as stream bank sedge meadows and wet prairies. This highly invasive thistle prevents the coexistence of other plant species through shading, competition for soil resources, and possibly through the release of chemical toxins poisonous to other plants.