n.
Weedy species of Cirsium , Carduus , Echinops , Sonchus , and other plant genera of the composite family .
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. 243