Home Gardening Center Tip Sheet: Exotic Azalea Species

By Sonia Uyterhoeven

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Exotic Azalea Species

The genus Rhododendron, which includes all azaleas and rhododendrons, comprises more than 1,000 species worldwide. The majority of all 70 species of azaleas are indigenous to the Northern Hemisphere, with a range from North America to Europe and Asia. Deciduous azaleas, which lose their leaves in winter, are native to eastern Asia, Europe, and North America, while evergreen azaleas are found only in Asia. Asian azaleas are generally not as hardy as, and are often crossed with hardier, European or North American species.

Deciduous azaleas tend to have an open, loosely branched habit. Evergreen azaleas have either an upright or sprawling habit and tend to be more densely branched than deciduous azaleas. Evergreen azaleas often have wide showy flowers that are disproportionately large compared with the foliage while deciduous azaleas have long tubular flowers that are in proportion to the foliage. The flowers on deciduous azaleas shrivel up and shed quickly while evergreen azaleas tend to hold on to their flowers after they turn brown and can look a little messy.

Evergreen azaleas are dimorphic, meaning they have two kinds of leaves. One set of leaves appears in spring around flowering time. They last for the season and then yellow and fall off in autumn. Another set of leaves is formed in early summer. These leaves last for 1 to 3 years and are thicker and smaller, and leathery.

Following are some of the European and Asian species and their cultivars you will find in the Azalea Garden at The New York Botanical Garden.

Deciduous European and Asian Azaleas

Rhododendron luteum (Pontiac azalea) - Native to Eastern Europe from the Ukraine to Turkey, this azalea is related to R. austrinum (Florida azalea). Found growing along streams and in swamps, the Pontiac azalea usually reaches 4 to 6 feet in height and, ultimately, up to 8 to 10 feet. Its fragrant yellow flowers open in May. Cultivars: 'Bee Dazzler', 'Golden Comet'

Rhododendron molle subsp. japonicum (Japanese azalea) - This showy upright azalea grows 4 to 8 feet tall with fragrant May flowers ranging from yellow to red in color. It foliage turns red in fall.

Rhododendron mucronulatum (Korean azalea/rhododendron) - Classified either as an azalea or deciduous rhododendron, this species is known as a harbinger of spring because its purplish flowers bloom in late March to early April. It grows erect to an average of 6 feet tall and has colorful autumn foliage. Cultivars: 'Cornell Pink', 'Crater's Edge', 'Easter Bunny', 'Pink Peignoir'

Rhododendron quinquefolium (five leaf azalea, cork bark azalea) - In its shady, high elevation mountainous habitat, this azalea grows to 15 feet tall, but in a garden setting it generally stays compact, reaching only 3 to 4 feet. Its whorls of five leaves start out green, become outlined in red, and then turn a brilliant red in fall. It has white pendulous flowers that bloom in early May; the older stems become fissured like cork bark.

Rhododendron schlippenbachii (Royal azalea) - This azalea grows 6 feet tall and wide, forming a globe shape. Its pale- to rose-pink flowers open in early May. Densely branched, its egg-shaped leaves in whorls of five will turn colorful in fall if grown in sun.

Rhododendron yedoense var. poukhanense (Korean azalea) - This compact azalea grows 3 to 6 feet tall and equally as wide. Its lightly fragrant, rose to lilac flowers bloom in early May. The foliage turns orange to red-purple in fall. Cultivar: 'Rosea'

Evergreen Asian Azaleas

Rhododendron indicum (sweet indica azalea) - This slow-growing evergreen azalea is often used in creating bonsai. It grows 3 to 6 feet tall and has reddish-purple flowers in late May. Cultivar: 'Flame Creeper'

Rhododendron kiusianum (Kyushu azalea) - A slow- and low-growing semi-evergreen with a spreading form, this azalea reaches 3 feet tall and 5 feet wide. Its flowers, in colors of salmon, pink, lavender, or white, bloom in late May. Cultivar: 'Album'

Rhododendron marcrosepalum (big sepal azalea) - Found in well-drained soil in woodlands and open thickets in Japan, this semi-evergreen azalea grows 3 to 6 feet tall. It has hairy leaves, and its light-purple-red, fragrant flowers bloom in May.

Rhododendron mucronatum (snow azalea) - This semi-evergreen azalea grows 4 to 6 feet tall with fragrant pinkish-white flowers that open in May.

Rhododendron nakaharae (dwarf azalea) - This spreading azalea from northern Taiwan, with a maximum height of 1 foot and a spread of 3 to 4 feet, is often used as a groundcover. It prefers sun or part shade over full shade. Its orange-red flowers bloom in late June. Cultivar: 'Mount Seven Star'

Rhododendron stenopetalum 'Linearifolium' (spider azalea) - This semi-evergreen that grows to about 3 feet tall is known for its long, narrow, spidery leaves, which take on a reddish cast in winter. The purple-pink to purple-red flowers echo the form of the foliage. This unusual azalea appeals to collectors and people who like oddities.

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