Canada thistle is a complex-root-spreading perennial that reproduces primarily by rhizomes and, to a lesser extent, by seeds. The flowers are usually purple or light pink but can also be white. Each plant is either male or female and requires pollination of the female flowers to produce viable seed. Due to its extensive root system, large patches are often male or female—seldom both. Leaves are usually lance-shaped, irregular, and divided into spiny-tipped lobes.
Canada thistle is one of the most invasive species ever introduced. It was one of the first plants to have noxious weed laws requiring its control: first in Vermont in 1795, followed by New York in 1831.
In Teton County, it has invaded fields, rangelands, turf, roadsides, riparian areas, and many other places with a vast variety of environmental conditions.
For advice on controlling this invader or for a free consultation of your Teton County residence, please contact Teton County Weed & Pest District at 733-8419.