thistle

Weedy species of Cirsium, Carduus, Echinops, Sonchus, and other plant genera of the aster family (Asteraceae). The term usually refers to prickly leaved species of Carduus and Cirsium, which have dense heads of small, usually pink or purple flowers. Because they have spiny stems and flower heads without ray flowers, Carduus species are called plumeless thistles. Canadian thistle (Cirsium arvense) is an attractive but troublesome weed in agricultural areas of North America. The thistle is the national emblem of Scotland. 1044

Find more information on thistle. Upgrade to Britannica Online for more on thistle.