All of the remaining 12 species of IDENTIFYING THE NATIVE AZALEAS Rhododendron subsection Pentanthera oc- cur in the southeastern U.S. The easi- Dr. Kathleen A. Kron est first line of investigation for iden- Winston-Salem, NC tification purposes is flower color. Three main groups can be identified using this criterion: (1) white, (2) pink, The deciduous azaleas are among the showiest of our native shrubs. Their and (3) orange to red. Within these primary beauty is due to their flowers, which range in color from white to color groups the timing of flowering pink, and orange to red. Early in the history of European plant collecting in and leaf expansion, the type of pubes- this country, native azaleas were used to develop numerous cultivars (Ghent, cence (hairs) and characteristics of the Knap Hill, Exbury, and Mollis azaleas). These cultivar azaleas were the result flower bud scales are useful characters of initial crosses of Rhododendron molle (from China and Japan) and the North for identifying species. American azaleas, or Rhododendron luteum (from the Caucasus region) and the North American azaleas. Although these cultivars offer marvelous displays of Among the white-flowered group are color in the spring, the native azaleas have their own delicate beauty. Rhododendron alabamense, R. arborescens, R. atlanticum, and R. viscosum. Like other members of the genus Rhododendron, the native azaleas have the Although the flowers of these species petals fused into a funnel or cup-shaped corolla. Most of the native azaleas are consistently white, they may oc- belong to a subgroup of rhododendrons named R. section Pentanthera [Rhodo- casionally be pale pink or tinged with dendron vaseyi, a rare azalea found in the southern Appalachians, is in the pink. Of these, R. alabamense is unique closely related R. section Rhodora (1)]. The members of R. section Pentanthera because it possesses a yellow blotch share several unique characters that indicate a unique common ancestry. These on the upper corolla lobe and a very characters include a narrow corolla tube and five stamens that are much longer delicate sweet fragrance. This azalea than the petals. Several members of the section have a darker-colored blotch is almost entirely confined to Alabama on the upper petal, others lack this blotch. This is in contrast to the evergreen and its periphery. It flowers early in azaleas (Rhododendron subgenus Tsutsusi) that have spotted petals, usually ten the spring, before the leaves are ex- stamens that are not much longer than the petals, and wide corolla tubes. panded. Rhododendron atlanticum is re- stricted to the Atlantic Coastal Plain. There are 15 species of R. section Pentanthera. Rhododendron molle (Mollis It is usually a strongly rhizomatous azalea, R. subsection Sinensia) is the most distinctive of the Pentanthera shrub, often less than a meter in azaleas. It has a broader corolla tube than the other members of section, with height, growing in acid sands. The spots on the interior surface. Its color ranges from yellow, in China and Japan, flowers of R. atlanticum bloom before to orange-red, in Japan only. This species has been extensively used in the the leaves expand and have a very development of many cultivars of azaleas. The remaining 14 species of section strong musky-sweet odor. The flow- Pentanthera (R. subsection Pentanthera) are very closely related and therefore ers are densely covered with gland- the differences among these species are often subtle. All of these species tipped hairs that are extremely sticky. possess a narrow corolla tube and stamens that extend beyond the end of the Rhododendron arborescens and R. petals. These azaleas occur as understory shrubs, often under a canopy of viscosum are two closely related oaks. They are less frequent on north-facing slopes because, although they are understory plants, they require a fair amount of sunshine. If the canopy is too dense, azaleas will be absent. They can vary in height from less than a meter to ten meters tall. Although in the past most of the azaleas were reported as non- rhizomatous, they are actually often rhizomatous or stoloniferous. Two species occur outside of the southeastern United States. Rhododendron occidentale (Western azalea) occurs along the west coast of southern Oregon to southern California. This species is extremely variable in flower color, but is generally white with a yellow blotch on the upper corolla lobe. It is the only member of R. section Pentanthera that occurs along the west coast. Rhododen- dron luteum (Pontic azalea) is native to the Black Sea and Caucasus region. Its flowers are bright yellow with a deeper yellow blotch. This species is reputed to have caused Alexander the Great's troops to fall ill after eating honey made from its flowers. This is likely due to the andromedotoxin that is prevalent in the nectar R. viscosum, the clammy azalea of many members of the genus Rhododendron. 72 • THE AZALEAN/December 1996 species with white flowers that bloom The pink group of decidu- after the leaves have expanded. Rhodo- ous azaleas are all early flow- dendron arborescens is restricted to the ering species that bloom be- mountains, and the flowers have a fore the leaves are fully ex- bright red style with a cinnamon-like panded. These azaleas are R. fragrance. The entire plant of R. periclymenoides (Piedmont aza- arborescens is smooth and shining due lea), R. canescens (sweet aza- to the lack of soft white (unicellular) lea), and R. prinophyllum hairs that are usually common on (roseshell azalea). Their flow- plants of R. viscosum. ers range in color from pale pink (almost white) to a deep The most widespread species of cherry color and all lack a deciduous azalea is the clammy aza- blotch on the upper corolla lobe. lea, Rhododendron viscosum. Its geo- Rhododendron prinophyllum graphic distribution ranges from Maine can be distinguished from the south to peninsular Florida, west to other two pink azaleas by its eastern Texas and from eastern Okla- longer flower stalks (pedicels) homa to southern Arkansas east to the covered with gland-tipped Atlantic coast. This is the most vari- hairs, a broader corolla R. calendulaceum, the flame azalea able of the southeastern azaleas and tube, gland-tipped hairs on has been divided into several segre- the margins of the sepals and gate species: R. coryi, R. oblongifolium, on the ovary, and conspicuously well as gland-tipped hairs. This is in and R. serrulatum. In the northern part fringed (ciliate) leaf margins. This aza- contrast to the closely related R. peric- of its range the white corolla is often lea is more northern in its distribution lymenoides, which has very few unicel- tinged with pink. The flower bud than R. canescens, which is restricted lular hairs on the bud scales and scales of this species often have a dis- to the southern Coastal Plain. It is the corollas lacking gland-tipped hairs. tinctive dark brown line around the only pink azalea that occurs in Arkan- edges. This characteristic has been sas and Oklahoma, as well as in the There are five species that have used to separate R. serrulatum from R. northeast as far north as New Hamp- orange to red flowers—R. austrinum, R. viscosum in the southeast, where the shire. Because it is often covered with calendulaceum, R. flammeum, R. dark brown band is most common. soft unicelluar hairs it has been con- cumberlandense, and R. prunifolium. The However, the dark brown line can be fused with R. canescens. However, R. plumleaf azalea, R. prunifolium, is the found far north in some populations canescens has very narrow corolla tubes rarest of the deciduous azaleas and has of R. viscosum. Rhododendron coryi and and the fruits lack the gland-tipped been proposed for federally endan- R. oblongifolium have been separated hairs common in R. prinophyllum. gered status. Restricted to just a few from R. viscosum due to their long nar- Rhododendron canescens is common in counties on the southern Alabama- row corolla tubes. Plants named R. swamps or bottomlands in the Gulf Georgia border, R. prunifolium flowers coryi are stoloniferous in habit, Coastal Plain. This azalea has a sweet, after the leaves have expanded. Its whereas plants named R. oblongifolium sometimes slightly musky odor and deep red-orange to apricot-colored have hairier leaves than many indi- flowers just before or as the leaves ex- flowers essentially lack any hairs, and viduals of R. viscosum. However, all pand. Rhododendron of these "species" have white flowers canescens is very variable with gland-tipped hairs that are in in pubescence (hairi- lines up the outside of the corolla tube. ness) and in corolla They lack a blotch on the upper co- color. In some Missis- rolla lobe and have greenish-whitish sippi populations R. colored filaments and styles. They all canescens has such flower after the leaves have fully ex- densely hairy (unicellu- panded and have a sweet-musky fra- lar hairs) leaves that grance. When all of the characters are they appear whitish. compared over the entire range of The flower bud scales of Rhododendron viscosum it is apparent R. canescens are also of- that R. coryi, R. oblongifolium. and R. ten white with dense serrulatum represent random local vari- hairs. The outer sur- ants of R. viscosum, and therefore face of the corolla is should not be recognized as distinct densely covered with R. prunifolium, the plumleaf azalea, species. unicellular hairs as at Calloway Gardens December 1996/THE AZALEAN • 73 the bud scales and leaves are also calendulaceum (flame azalea) is a com- upper corolla lobe) the hybrid indi- smooth and shining. This species is mon component of the understory in viduals are easy to identify.