Canada thistle (Cirsium arvense)
Appearance: Perennial herbaceous plant, 2 - 5' tall with slender grooved stems that branch only at the top. It has male and female plants.
Leaves: Alternate, smooth, oblong, tapering, and directly attached to the stem, deeply divided, with prickly margins.
Flowers: Numerous small purple flowers appear on top of the upper branched stems between June and September.
Seeds: Small light brown seeds are tufted for dispersal by the wind. Seeds remain viable in the soil for over 20 years.
Roots: Each plant has a fibrous taproot with wide spreading horizontal roots. Each small section of root can form a new plant enabling the plant to spread vegetatively.
- Video on Canada thistle identification (University of Wisconsin)
- Minnesota Department of Agriculture Thistle Identification
- Canada Thistle Fact Sheet (MDA)
- Minnesota Noxious Weeds (MN DOT)
- University of Minnesota Extension
- MISIN Canada thistle identification training module
- US Forest Service Fact Sheet
- Plant Conservation Alliance Fact Sheet
- Invasive and Native Thistle Identification (South Dakota State University)