Original sold The milk thistle is a thistle of the genus Silybum Adans., a flowering plant of the daisy family Asteraceae. They are native to the Mediterranean regions of Europe, North Africa and the Middle East. The name ‘milk thistle’ derives from two features of the leaves: they are mottled with splashes of white and they contain a milky sap. I grew this magnificent specimen in my garden in Vancouver, Canada, primarily for the seeds, they protect the liver against toxins, and have other therapeutic properties and possible medical uses. It also became one of my subjects as have so many of the plants I grow.