This spiny, troublesome perennial is probably hated more than any other weed. Its primary offense has been the destruction of millions of dollars worth of agricultural crops each year. In lawns, its sharp spines cause much discomfort to the touch, and its aggressive growth habits crowd and destroy good turf. Canada thistle is such a serious pest that most states have passed legislation making it an offense to allow it to reach maturity. Seed laws are also exceptionally rigid against Canada thistle. Leaves are smooth, shiny green on the upper surface, with crinkled, spiny margins. Flowers are bright lavender, with male and female in separate plants. Canada thistle spreads by deep rhizomes.