Silybum Marianum. Non-Irradiated. Silymarin is the well-known component in the seeds believed to play a major role in the action of milk thistle. (Silymarin is not actually a single compound but the collective name for a group of related compounds [flavonolignans] that includes silibinin silydianin and silychristin). It's naturally present in the seeds at 1 to 5% but standardized extracts and formulations are often concentrated so they contain 70 to80% silymarin.