The hydrangea, a member of the family Saxifragaceae, is the only flower featured on this set of stamps not belonging to the composite family. Native to Asia and the Americas, hydrangeas are deciduous shrubs notable for their enormous clusters of white, pink, or blue flowers. The color of the flowers can be changed by varying the pH of the soil, with acidic soil producing blue- and mauve-colored blooms and alkaline soil producing pink. The most widely-grown of all hydrangeas is the grandiflora, or hills-of-snow, variety. Young plants may grown up to five feet in a single season, eventually reaching fifteen to twenty feet in height.