Tansy (Tanacetum vulgare) is a perennial, herbaceous flowering plant of the aster family, native to temperate Europe and Asia. It has been introduced to other parts of the world and in some areas has become invasive. It is also known as Common Tansy, Bitter Buttons, Cow Bitter, Mugwort, or Golden Buttons.
Tansy is a flowering herbaceous plant with finely divided compound leaves and yellow, button-like flowers. It has a stout, somewhat reddish, erect stem, usually smooth, 50–150 cm tall, and branching near the top. The leaves are alternate, 10–15 cm long and are pinnately lobed, divided almost to the center into about seven pairs of segments, or lobes, which are again divided into smaller lobes having saw-toothed edges, giving the leaf a somewhat fernlike appearance. The roundish, flat-topped, button-like, yellow flower heads are produced in terminal clusters from mid-to-late summer. The scent is similar to that of camphor with hints of rosemary. The leaves and flowers are toxic if consumed in large quantities; the volatile oil contains toxic compounds including thujone, which can cause convulsions and liver and brain damage. Some insects, notably the tansy beetle Chrysolina graminis, have evolved resistance to the toxins and subsist almost exclusively on the plant.
Tansy is native to Eurasia; it is found in almost all parts of mainland Europe. It is absent from Siberia and some of the Mediterranean islands. The ancient Greeks may have been the first to cultivate it as a medicinal herb. In the sixteenth century it was considered to be "necessary for a garden" in Britain.
Tansy has a long history of use. It was first recorded as being cultivated by the ancient Greeks for medicinal purposes. In the 8th century AD it was grown in the herb gardens of Charlemagne and by Benedictine monks of the Swiss monastery of Saint Gall. Tansy was used to treat intestinal worms, rheumatism, digestive problems, fevers, sores, and to “bring out” measles.
During the Middle Ages and later, high doses were used to induce abortions. Contradictorily, tansy was also used to help women conceive and to prevent miscarriages. In the 15th century, Christians began serving tansy with Lenten meals to commemorate the bitter herbs eaten by the Israelites. Tansy was thought to have the added Lenten benefits of controlling flatulence brought on by days of eating fish and pulses and of preventing the intestinal worms believed to be caused by eating fish during Lent.