Commemorating Paeon, an ancient Greek physician, is said to have first used P. officinalis medicinally. Although the genus has long been considered a member of the buttercup family, Ranunculaceae, some modern botanists now place it in a family of its own, Paeoniaceae. A genus of 33 species of hardy herbaceous and shrubby perennials and a few shrubs, among the noblest and most decorative plants for a sunny or shaded border. The main division of the genus is between the herbaceous and the tree paeony, but botanically, the matter is much more complex.