Canada Thistle (Cirsium arvense)
Sunflower Family (Asteraceae)
University of Idaho
Description: Dioecious perennial from deep creeping rootstocks. Stems 1 to 4 feet (0.3 to 1.2 meters), rigid, smooth to slightly hairy, branched at top. Leaves variable light to dark green, sessile, oblong or lance shaped, divided into spiny tipped lobes. Either male or female flowers present, light lavender to purple, 3/8 to 3/4 inch (1 to 2 cm) in diameter, in several to many headed clusters. Phyllaries spineless. Seeds 1/8 inch (.32 cm) long, brownish, with a protrusion at one end, and a tuft of hairs at the top.
Habitat: Native to Europe. Invades cropland, meadows, pastures, roadsides, clearcuts, and waste areas. The extensive underground root system can penetrate the soil as deep as 10 feet (3 meters) and grow laterally 12 to 15 feet (3.6 to 4.5 meters) a year. Randomly spaced root buds can develop new shoots under the right environmental conditions.
Distribution: Canada thistle is fairly widespread throughout northern California and can be seen along most waterways.
Flowering Period: July to August.