This section is from the book "Handbook Of Hardy Trees, Shrubs, And Herbaceous Plants", by W. Botting Hemsley. Also available from Amazon: Handbook of hardy trees, shrubs, and herbaceous plants.
Herbs or small shrubs with tufted radical and alternate entire exstipulate glabrous cauline leaves, and involucrate capitules of flowers. Calyx persistent, 5-lobed, lobes quincun-cial in bud. Corolla 5-lobed; lobes narrow, usually unequal. Stamens 4, inserted in the tube of the corolla, and alternate with its lobes, the fifth between the two upper lobes being deficient. Fruit a dry 1-celled 1-seeded indehiscent achene. This order is limited to one genus of few species, inhabiting the Mediterranean region.