Milk thistle seed is used as a liver tonic, to "support healthy liver function*" and overall well being. The hard, dark-colored seeds are ground and used to make a tea or tincture, encapsulated, or added to foods. The whole seeds are also sometimes added to foods.

Botanical name: Silybum marianum

Milk thistle has been cultivated for two thousand years. Used as a vegetable in Europe, all parts of the plant — leaves, stalks, roots, flower buds and seeds — were prepared as a food (after removal of the thorns, of course). Various herbal uses of the seed were described as early as the first century. It was mentioned often in herbals of the Middles Ages, and by the mid-1900s, clinical research on milk thistle was developing. Today, few herbs are as well-studied as milk thistle and its constituents.

Milk thistle seeds (fruits) are harvested in the late summer or fall, when they're fully ripe. The seeds have silky white hairs (pappus) attached; these fall off as the seeds are harvested and dried or during threshing of the seed. When caught by the wind, however, these hairs help spread the seed — which explains how milk thistle can quickly escape cultivation and plant itself wherever the wind blows it.

The sharp, spiny bracts that surround the seed head make it hard to hand-harvest the seeds safely, even with gloves. And commercial harvest, using a combine, is challenging because the seeds don't all ripen at the same time. Overripe pods can drop their seeds onto the ground, or the seeds can go flying off to another field. Under-ripe seeds, on the other hand, are poor quality and low in desired constituents. Breeding programs are working to standardize the ripening time of milk thistle while increasing the natural levels of silymarin. These new varieties will increase yields and improve quality.

Constituents of Note: Silymarin is the well-known component in the seeds, believed to play the 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 [fllavonolignans] 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 to 80% silymarin.

Milk thistle also contains 20 to 50% of a fixed oil composed of about two-thirds linoleic acid.

Did you know? Early Christian tradition held that a drop of Mary's milk spilt on a milk thistle leaf, causing the white marbling on the leaves — and leading to the common name of milk thistle. One of milk thistle's other names, Marian thistle, as well as the species name, mariannum, are derived from the name Mary. The plant was dedicated to Mary and often appears along with Mary in Medieval art. Other common names for this plant include St. Mary's thistle and Our Lady's thistle.