Rhododendron is a genus of more than 1,000 species and more than 25,000 cultivars and hybrids. They grow as native plants in many parts of the world, including North America. By far, the largest number of wild rhododendrons are native to Asia, and it is those species that many of the cultivated rhododendrons are derived.

Rhododendrons and azaleas are both classified in the genus Rhododendron, though they are differentiated by several characteristics: Rhododendrons are generally larger than azaleas. Rhododendrons are strictly evergreen, while azaleas may be deciduous or evergreen.

Rhododendrons (hybrids, as well as subgenera Azaleastrum, Choniastrum, Hymenanthes, Rhododendron, and Therorhodion) are larger overall with thicker, bigger leaves and larger flowers than azaleas. Rhododendrons have fewer stems, more stamens, and the leaves are smooth, not hairy. Azaleas bloom earlier and have a wider range of colors.

Rhododendrons are actually the most popular woody landscape plant in the United States. There are over 800 species of rhododendrons ranging from spreading groundcovers a few inches high to 100 foot tall trees and many thousands of registered, named varieties. Twenty-four species of rhododendron are native to North America. Some are wild.