Following are some of the European and Asian species and their cultivars that you may find in the Azalea Garden at The New York Botanical Garden.
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: R. ‘Bee Dazzler’, R. ‘Golden Comet’
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.
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: R. ‘Cornell Pink’, R. ‘Crater’s Edge’, R. ‘Easter Bunny’, R. ‘Pink Peignoir’
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.
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.
This compact azalea grows 3 to 6 feet tall and equally as wide. It’s lightly fragrant, rose to lilac flowers bloom in early May. The foliage turns orange to red-purple in fall.
Cultivar: R. ‘Rosea’
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: R. ‘Flame Creeper’
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: R. ‘Album’
This semi-evergreen azalea grows 4 to 6 feet tall with fragrant, pinkish-white flowers that open in May.
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: R. ‘Mount Seven Star’
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.
Rhododendrons & azaleas : a colour guide by 
Rhododendrons and Azaleas by 
Success with Rhododendrons and Azaleas by 
The Timber Press Encyclopedia of Flowering Shrubs by 
