There are ornamental qualities associated with all plum trees, as all produce attractive flowers in spring. While all plums have the potential to form edible fruits, not all form perfectly sized or good tasting types. Therefore, some plums are grown only for beauty.
Plum trees (Prunus spp.) are regarded for the beauty of their springtime flower display. If pollinated by bees, these flowers develop into edible fruits of varying size, color and flavor.
Plum trees that demonstrate a regular, annual production of quality, tasty fruits after flowering are generally called "edible plum" varieties. These trees also produce larger numbers of fruits.
Ornamental plums are selected for gardens based on aesthetics, such as prolific flowering, foliage color or sheen. These trees may set fruits, but often they are very small, sporadic, or taste poor.
Plum trees that produce flowers followed by edible fruits serve a dual purpose of providing ornamental beauty in spring while in blossom, followed by productivity in fruits.
Although a plum tree may be marketed as an edible fruit tree selection, the personal taste of a gardener can trump the designation. If you do not like the amount, color, size or flavor of the fruit the edible fruit tree produces, arguably it serves only an ornamental purpose: enjoying the flowers and the fall foliage color, for example.