State Noxious Weed List - Yes

Growth form: Perennial spreading by both seed and root. Usually grows 2 to 3 feet tall with alternate, dark green leaves. The leaves are oblong, usually deeply lobed, and have spiny toothed edges. Canada thistle is dioecious, so cross pollination is necessary for seed production. Many ecotypes exist and flower color can vary from purple to light lavender to white. Stem color can vary from green to lavender. Rosette leaves are shiny green with spiny tips. Plants require at least 14 hours of daylenth to bolt and flower. The roots are fleshy, creeping, and grow deeper in clay or muck soils than in sand or gravel (20 feet). Flowers produce 40 to 80 seeds per head and can move long distances, although most seed remain in the head until winter and eventually germinate nearby.

Canada thistle grows best in the northern portion of the US, where temperature and rainfall are moderate. The roots have medicinal uses.