Silybum (milk thistle) is a genus of two species of thistles in the (daisy family). The plants are native to the Mediterranean regions of Europe, North Africa, and the Middle East. One species has been introduced elsewhere, including in North America. The name "milk thistle" derives from a feature of the leaves, which are prominently banded with splashes of white. Historically, these milky bands were said to be Mother Mary's milk, and this is the origin of another common name, St.