This family contains herbs, shrubs and trees and is distinguished by having leaves that are positioned opposite each other and the plant producing a milky sap. Flowers are tubular with five petals. The family includes periwinkle and, in a subfamily of their own, milkweed and butterfly weed. The flowers of the milkweed subfamily are unusual in shape. Many members also have a corona, or a crown-like addition consisting of five “hoods” that look like petals and face the center of the flower. The five real petals bend backward. Five stamens are fused to the ovary. Once mature, the fruit turns into a large, dry pod.