Silybum 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. 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. Mary's thistle. The most widespread species is Silybum marianum. Many years of research show the active flavanoid-lignan group of constituents, called silymarin, contained only in the seed shell has liver-protective and regenerative properties, as well as antioxidant effects. The liver-protective effects were known and written about in ancient times, leading to the active chemical, pharmacological, and safety research beginning in Germany in the 1950s. Clinical use for a variety of liver ailments, such as hepatitis, has also prospered throughout many parts of the world.