Milk thistle

This striking member of the daisy family has thorny, variegated foliage and purple blooms that resemble large thistles. Remove the blooms before seeds mature to prevent the plant from self-seeding and becoming weedy. When cut, the plant produces a white, milky liquid, which is how it got its name. The plant has been used for centuries as a treatment for diseases of the liver and gallbladder. In its native range, it is an annual, but it may overwinter in Zones 5-9.