(Silybum marianum) Large, showy plants reach 1 metre or more in height and produce beautiful spiny, purple flowers in late summer. Glossy leaves have white veining making them a real standout in the herb or perennial garden. The seeds are traditionally used as a liver tonic. If not using the seeds, remove spent flowers to keep plants from self seeding as they can become weedy. Plants can be annual or biennial and prefer full sun. Start indoors or direct seed.