Flowers of Feverfew, Tanacetum parthenium (Chrysanthemum parthenium, Pyrethrum parthenium), growing in Norfolk, UK, July. The picture shows the the characteristic yellowish green hue of the foliage and the composite floral heads. Feverfew is a member of the daisy family ( Asteraceae ); each "flower" consists of a large number of individual florets. Those in the centre (yellow) are called disc florets; those at the edge ( corresponding in appearance to the petals of a simple flower) are known as ray florets ( here white). Feverfew is native to the Balkans, but now widespread throughout Europe. It is used in herbal medicine to treat the symptoms of migraine. The principal active chemical in feverfew preparations is parthenolide. Parthenolide is a complex lactone which has been shown to have anti-cancer properties in vitro, but is impractical for drug use due to its low water solubility.