Cirsium arvense

Canada thistle

Family: Asteraceae · Type: perennial · Not Native

Conservation status: Cal-IPC Yes

Canada thistle is a naturalized perennial herb found in northwestern California, the Cascade Range, Sierra Nevada, San Francisco Bay Area, northern and southern coastal regions, and the Great Basin in disturbed areas at elevations below 2,450 meters. Flowering from June to September, this plant produces purple (occasionally white or pink) flowers in rounded or flat-topped clusters with heads 1 to 2 centimeters wide. Growing with colonial stems 50 to 100 centimeters tall, it spreads through runner roots and has green to gray-tomentose herbage. Its leaves are 3 to 30 centimeters long, mostly along the stem, with spiny edges and gradually reduced in size toward the stem tip. The plant forms dense colonies in disturbed landscapes, with each stem producing multiple flower heads and spreading aggressively through underground root systems.

Habitat: Disturbed areas

Bloom period: Jun-Sep

Elevation: < 2450 m

Bioregions: NW, CaR, SN, SnFrB, n SCoRI, SCo, GB

Data from The California Species Project — 14,000+ California species with verified data from CNPS, CDFW, USFWS, Jepson eFlora, Cal-IPC, and more.