This story on the USPS stamp collector's website should be of interest to all Bonsai aficionados:

With these five stamps, the U.S. Postal Service celebrates the beauty of bonsai. The word “bonsai” (Japanese for “plant in a pot”) refers to the art of cultivating plants — usually trees — in trays, pots, or other containers. Favorite bonsai plants include evergreens, maples, and azaleas, but many other trees and shrubs are also suitable. This horticultural art form has become popular in many parts of the world. A large number of bonsai are on permanent display in Washington, D.C., at the United States National Arboretum.

One of the common styles of bonsai is shown on each of these five stamps. The first stamp depicts a Sierra juniper in semi-cascade style, in which the tip projects over the pot rim but does not extend below the base. Second is a trident maple in informal upright style, in which the trunk bends slightly to the left or right. Third is a black pine in formal upright style, with the trunk straight and tapering evenly, with symmetrical branches, from base to apex. Fourth is an azalea plant in multiple-trunk style, with several trunks emerging from one root system. The fifth and final stamp shows a banyan in cascade style, in which the trunk evokes a stream flowing down a mountainside, with the tip extending below the pot’s base. The plants depicted are roughly 15 to 20 inches tall.

Read the whole story on their website