Silibinin (INN), also known as silybin (both from Silybum, the generic name of the plant from which it is extracted), is the major active constituent of silymarin, a standardized extract of the milk thistle, containing a mixture of flavonolignans consisting of silibinin, isosilibinin, silychristin, silidianin, and others. Silibinin itself is a mixture of two diastereomers, silybin A and silybin B, in approximately equimolar ratio. Silibinin is used in pure forms as a medication, and more frequently as an active ingredient in milk thistle–derived herbal supplements.
Biosynthesis of silybin (silibinin A and silibinin B)
Silybum is a genus of two species of thistles in the family Asteraceae. 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. Mary's thistle. The most widespread species is Silybum marianum.
Silybum
Dried thistle flowers at the end of summer
Flowerhead of Silybum marianum