Left: Silybum marianum, the Marian thistle, is also known as milk thistle, because of the milky-white streaks on the spiny leaves; right: The thistle appears outside and below the enclosure of the captive Unicorn, near the Madonna lily (Lilium candidum), another plant associated with the Virgin. Visit the Collection Database to see the detail in context and learn more about The Unicorn in Captivity.
While thistles were a thorn in the farmer’s side, then as now, virtually all plants were accorded medicinal value in the Middle Ages. Milk thistle (Silybum marianum) was eaten as a vegetable, and is grown in a bed devoted to pottage plants here at The Cloisters, but it has a rightful place in the medicinal collection as well. According to the Grand Herbier, this thistle was believed to increase the flow of mother’s milk, and help women to nourish their children. (Margaret Freeman, The Unicorn Tapestries, 1976.) The Hortus Sanitatis gives a long list of medicinal virtues, including the capacity to relieve the thirst of infants bitten by venomous creatures. (Frank Anderson, German Herbals to 1500, 1984.) Many if not most of us have seen milk thistle capsules on the shelves of drugstores or of health food stores; modern research indicates that the plant can help to repair damaged liver tissue.
I have seen milk thistle grown as an ornamental in England, and it does make an attractive foliage plant, but it is necessary to cut back the flowering stems as they emerge. Once the milk thistle blooms, it will no longer produce leaves, but will quickly go to seed. The purplish-pink flower head is attractive, but as with all thistles, the head should be removed before the seed disperses. (The flower of the milk thistle in the detail from The Unicorn in Captivity appears to be white, but when seen from the reverse side of the tapestry, the flower shows pink. Exposure to light has faded some of the original colors.)
As with other medieval European species once prized as healing plants, the milk thistle is considered to be an agricultural weed in the United States. Despite the medicinal virtues of thistles, medieval agriculturalists liked them no better than today’s farmers, and they equipped themselves with a thick leather mitt when dealing with these plants. Many ingenious methods of weed control were devised in the Middle Ages, including the use of two weed hooks that could be used in tandem as the weeder systematically worked his or her way between furrows, pulling weeds free of the soil and laying them down to mulch the roots of the crop. (Dorothy Hartley, Lost Country Life, 1979.) Weeds were troublesome in lawns and gardens as well as in the fields. The great medieval theologian and scientist Albertus Magnus recommended pouring boiling water over the site where a lawn was to be laid, in order to kill the weed seeds.
In the Middle Ages, the symbolic connotations of thistles were altogether negative. They were inextricably bound up with the Fall of Man and the cursed ground mentioned in Genesis 3:18. There were no weeds in Paradise.