: Creeping thistle, Field thistle, Californian thistle
: This species is listed as a prohibited noxious weed by the Michigan Department of Agriculture. Canada thistle was introduced to North America from Europe in the early 1600s.
: Perennial, rhizomatous thistle ranging in height from 0.6-1.5 m (2-5 ft), forms large monocultures.
: Simple, alternate, lance-shaped, crinkly, tapering, irregular lobes and spiny toothed margins.
: Upright; slender and branching towards the top; becoming increasingly hairy with age.
: Numerous, purple-lavender in color, small flower heads, less than 2.5 cm (1 in) high, clustered at the tops of stems, fragrant; bloom June through September.
Fruit and seeds
: Seeds are small, light brown; tufts of hair attached to the tip for wind dispersal; one plant produces between 1500-5000 seeds, which can germinate 8-10 days after flowering begins and persist in the seed bank for up to 20 years.
: Found in disturbed open areas, roadsides, agricultural fields; invades prairie and riparian areas; salt-tolerant; shade intolerant.
: Primarily by creeping, laterally spreading rhizomes, but also by prolific seed production; dioecious, with separate male and female clones; some hermaphroditic forms.
: Native swamp thistle (Cirsium muticum
) has sticky flower heads; non-native weeds bull thistle (Cirsium vulgare
), European swamp thistle (C. palustre
), and musk thistle (Carduus nutans
) have spiny winged stems.
Monitoring and rapid response
: Monitor sunny, disturbed sites including degraded grasslands, open woodlands, edge habitats and restoration sites. Begin control efforts in highest quality areas; pull seedlings within 2.5 weeks after germination or they become perennial; Canada thistle is clonal; resprouts from root fragments. Herbicides are most effective with two applications per season: in spring, just before flowering, and in fall on new growth after mowing, treat all stems. Different strains of Canada thistle respond differently to the same herbicide; may require 5-10 years of ongoing efforts. This species is extremely difficult to eradicate - research control options thoroughly.
: The Michigan Natural Features Inventory
(MNFI) has partnered with MISIN to provide the information in this fact sheet. Species images and/or information were used with permission from "A Field Identification Guide to Invasive Plants in Michigan's Natural Communities
" and "A Field Guide to Invasive Plants of Aquatic and Wetland Habitats for Michigan