Canada thistle is an introduced, perennial herb that spreads from deep creeping rhizomes. The stems are leafy, thin, green, and 30 cm to 150 m tall. The leaves are alternate, lance-shaped, irregularly lobed and spiny, green above and white-hairy below. The base of the leaf does not clasp the stem. The small (1-2 cm) heads are composed of magenta pink disk flowers only, and either male or female on an individual plant. The involucral bracts are almost spineless. Canada thistle is common in fields, pastures, meadows, and roadsides at low to middle elevations and can be particularly abundant near agricultural land.