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These pages are the result of information I have picked up over 35 years at American Rhododendron Society meetings & conventions, in courses at Longwood Gardens, and in the numerous books which I have made available in the Rhododendron and Azalea Bookstore. The goal of this site is to share this information with those who share a love for the Genus Rhododendron. All proceeds from the Rhododendron and Azalea Bookstore are contributed to the ARS Research Fund and the Rhododendron Species Foundation.

RHODY      Genus Rhododendron

RHODYRhododendrons are shrubs of the genus Rhododendron which is in the heath family (family Ericaceae) which includes heathers, Kalmia (mountain laurels), blueberries and cranberries. Since almost all of these plants require acidic soil, they are often referred to as the family of acid-loving plants. Rhododendrons are found in the wild, chiefly in mountainous areas of the arctic and north temperate zones. They typically have large, shiny, leathery evergreen leaves and clusters of large pink, white, or purplish flowers. North American species include the great laurel, or rose bay (R. maximum), West Virginia's state flower; and the Western rhododendron (R. macrophyllum), Washington's state flower. Azaleas are in the same genus. Most cultivated rhododendrons are hybrids that are propagated from cuttings or tissue culture. Rhododendrons are referred to as the King of Shrubs since they are regarded by many as the best flowering evergreen plants for the temperate landscape.

Rhododendrons are shrubs for all seasons. In winter some stand out with large evergreen leaves. In spring the flowers are showy; throughout the summer and fall the leaves add a pleasing, deep green color to the garden. Some deciduous azaleas add bright fall color before the leaves drop. The spectacular spring flowers of azaleas and rhododendrons make them among the most popular garden shrubs.

There are 26 species of Rhododendron that are native to North America.

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RHODYAzaleas

Azaleas are shrubs of the genus Rhododendron and members of the heath family. There are 8 divisions of the genus Rhododendron. Azaleas comprise two of those divisions. Technically classified as rhododendrons, azaleas are generally more floriferous but have less impressive foliage. Typically non-azalea rhododendrons are evergreen and have flowers that are in trusses (a truss is a flower-like structure composed of many flowers). Typically an azalea is either evergreen with flowers singly rather than in a truss or are deciduous and may have flowers singly or in a ball-shaped truss.

When Linnaeus created the botanical grouping called genus Rhododendron in 1753, he created a separate genus for Azaleas containing 6 species. In 1796 Salisbury pointed out that Azaleas and Rhododendron could not be maintained as distinct genera. In 1834, George Don subdivided the genus Rhododendron into 8 sections. Azaleas comprise two of these sections, Subgenus Pentanthera typified by deciduous Rhododendron nudiflorum and Subgenus Tsutsusi typified by evergreen Rhododendron tsutsusi.

If flowers grow from terminal buds, new leaves and shoots grow from lateral buds and leaves are deciduous, then the rhododendron is an azalea in the Pentanthera subgenus.

If flowers and leaves grow from the same terminal buds, and the flowers have 5 to 10 stamens, then the rhododendron is an azalea in the Tsutsusi subgenus.

In 2004, these 8 subgenera were rearranged into 5 subgenera by Goetsch, et. al. Today, Azaleas are grouped into the Pentanthera Subgenus and Azaleastrum Subgenus.

Most grow in damp acid soils of hills and mountains, and are native to North America and Asia. Native American azaleas include the flame azalea (R. calendulaceum) and the fragrant white azalea (R. viscosum), also called swamp honeysuckle. Most of the brilliantly flowered garden varieties are from China and Japan. Some have deciduous leaves and are usually very hardy, while other are evergreen and frequently less hardy. The deciduous varieties are usually hard to propagate, but much progress had been made in this area. Evergreen varieties are usually easy to propagate. Many hybrid and species azaleas are in the commercial trade. They typically bloom early in the season and are popular for the color they add to the landscape.

One term that is used in describing many azaleas is hose-in-hose. This term is meant to describe what looks like a flower inside a flower. This actually is a flower with a large calyx. The sepals of the calyx are shaped like the petals of the corolla.

Another term that is more common with azaleas is double. A double flower looks like the interior is filled with petals. This is because the stamens grow into petal-like structures. The pistol may also be transformed into a petal-like structure or may be absent.

Another term is semi-double. In this case the stamens are partially transformed into petal-like structures. Occasionally extra petals are present and all stamens are present also.

Another version is hose-in-hose double. A perfect example of this is Gable's Rosebud azalea. The name is descriptive of the flowers appearance.

There are 16 species of Azaleas that are native to North America.

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Rhododendron and Azalea Web Pages

If you have a link to this site and I do not have a link to your site, please email so I can link to you.
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I want to extend a big Thank You to the following sites for their links to this site and I recommend others visit the sites of these enthusiastic Rhododendron and Azalea gardeners:

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The following links also have valuable information for Rhododendron and Azalea gardeners.

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Also a big Thank You to the following sites which gave nice reviews of this site and they may be helpful in finding links to other sites:

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