Rhododendron, an ornamental shrub or tree of the heath family. The name comes from the Greek for rose tree. Rhododendrons are grown as ornamentals for their showy flowers. The flowers are often spotted or blotched and range in color from white or yellow to pink, red, or purple. Rhododendrons vary in height from about 6 inches (15 cm) to 50 feet (15 m). They are native chiefly to the temperate zones of Asia, Australia, North America, and South America. Rhododendrons thrive in moist, shady regions with acidic soil containing organic matter, peat, or sandy loam. Many species are planted in the shade of tall trees.
The catawba rhododendron (also called mountain rosebay and purple laurel) grows to a height of 10 feet (3 m). It is found in mountains from West Virginia to Alabama. The great laurel (also called great rhododendron and rosebay) grows to 15 feet (4.6 m). It has rose-pink flowers and is the state flower of West Virginia. The pink rhododendron (or California rosebay) grows to 12 feet (3.7 m).
Botanists include azaleas and rhodoras with rhododendrons, since there are no consistent technical differences between the plants. However, gardeners usually consider them separate. Most azaleas are deciduous and have funnel-shaped flowers; most rhododendrons are evergreen and have bell-shaped flowers. Only one species of rhodora is cultivated—the purple-flowered one celebrated in Ralph Waldo Emerson's poem "The Rhodora." The rhododendron has a poisonous resin fatal to livestock.
Rhododendron is the genus name of azaleas, rhodoras, and rhododendrons; they belong to the family Ericaceae. The catawba rhododendron is R. catawbiense; great laurel, R. maximum; pink rhododendron, R. macrophyllum; rhodora, R. canadense. The tree rhododendron of Asia, R. arboreum, and the Caucasian rhododendron of Europe, R. caucasicum, have been used in developing many American hybrids.