The genus name, Rhododendron, is derived from rhodon for “rose” and dendron for “tree”. The genus is divided into 2 groups based on their leaves: deciduous azaleas (Carolina Azalea, Rhododendron minus var. minus, apparently didn’t get the memo) and evergreen rhododendrons. The Rhododendron species we see most often in the mountains are described below.
Smooth Azalea (Rhododendron arborescens)
- Location: Common. Found from low elevations up to 4,500 feet.
- Form: Tall deciduous shrub (often becoming tree-like). Twigs lack hairs (glabrous).
- Flowers: Fragrant white-to-pink tubular flowers with distinctive red stamens and style that extend beyond the petals.
- Leaves: Shiny green, turning red in the fall. Egg-shaped with rounded tips. Margins have small hairs, otherwise usually smooth.
- Fruit: Capsule with a few long hairs.
- Hybridizes readily with other deciduous azaleas, often making identification difficult, but the red style is an important identifying characteristic.
- Derivation of Scientific Name: From arbor for “tree-like”.
Flame Azalea (Rhododendron calendulaceum)
- Location: Common. Found in the mountains from mid elevations up to 5,000 feet.
- Form: Tall, leggy deciduous shrub or small tree.
- Flowers: Spectacular yellow, orange, or red tubular flowers with stamens that extend beyond the petals.
- Leaves: Light green, with hairs underneath.
- Fruit: A 5-lobed capsule.
- Derivation of Scientific Name: From “Calendula-colored” referring to the color of Calendula Marigolds.
Catawba Rhododendron; Mountain Rosebay (Rhododendron catawbiense)
- Location: Common. Found in the mountains from 4,000 to 6,500 feet.
- Form: Evergreen shrub or small tree.
- Flowers: Distinctive purple bell shaped flowers. Terminal flower buds lack leafy bracts.
- Leaves: Leathery, 4-5″ long, with rounded bases and bluntly pointed tips. Light colored below.
- Fruit: A 5-lobed capsule.
- Derivation of Scientific Name: Referring to the Catawba River, NC.
Rosebay; Great Laurel (Rhododendron maximum)
- Location: Common. Found from low elevations to 6,000 feet.
- Form: Large evergreen shrub or small tree. Often forms dense thickets (“Laurel Hells”) along streams.
- Flowers: Distinctive large white bell-shaped flowers with green/yellow spots on uppermost lobe. Terminal flower buds have leafy bracts. Blooms later than the other Rhododendron species.
- Leaves: Leathery, 5-8″ long, tapered at both ends. Woolly underneath.
- Fruit: A 5-lobed capsule.
- Derivation of Scientific Name: Referring to the large size of mature plants.
Piedmont Rhododendron (Rhododendron minus)
Some question whether there are two distinct species of Rhododendron minus in the Western Carolinas. However, Weakley includes both Rhododendron minus and Rhododendron minus var. minus in the “Flora of the Southeastern United States.”
- Location: Common. Found from low to high elevations. Has a greater range than Carolina Rhododendron (R. minus var. minus).
- Form: Tall, leggy, multi-stemmed evergreen shrub.
- Flowers: Usually pink-to-purple bell-shaped flowers with green/yellow spots on uppermost lobe. Corolla tube longer than corolla lobes (petals). Corolla lobes longer than those of R. minus var. minus. Calyx lobes (sepals) ovoid (egg-shaped). Blooms later than R. minus var. minus) despite usually growing at lower elevations.
- Leaves: Leathery, 2-4″ long, tapered at both ends. Smaller than those of R. maximum. Small dots or tiny holes underneath.
- Derivation of Scientific Name: Meaning “smaller”, probably referring to the size of the bloom and leaves.
Carolina Azalea (Rhododendron minus var. minus)
- Location: Uncommon. Usually found only at higher elevations.
- Form: Tall, leggy, multi-stemmed evergreen shrub.
- Flowers: Usually white bell-shaped flowers. Smaller than those of R. maximum. Corolla tube often shorter than corolla lobes. Corolla lobes shorter than those of Piedmont Rhododendron (R. minus). Calyx lobes deltoid (triangular) in shape.
- Blooms earlier than Piedmont Rhododendron (R. minus).
- Leaves: Leathery, 2-4″ long, tapered at both ends. Smaller than those of R. maximum. Small dots or tiny holes underneath.
- Derivation of Scientific Name: Meaning “smaller”, probably referring to the size of the bloom and leaves.
Pinxter Flower (Rhododendron periclymenoides)
- Location: Common. Found from low to high elevations.
- Form: Deciduous shrub.
- Flowers: Distinctive pink tubular flowers with stamens that extend beyond the petals.
- Leaves: Oblong to elliptic green leaves.
- Derivation of Scientific Name: Resembling a honeysuckle.
Pinkshell Azalea (Rhododendron vaseyi)
- Location: Rare. Found only at high elevations.
- Form: Deciduous shrub.
- Flowers: Distinctive pink flowers with short corolla tubes. Flowers appear in early spring before the leaves appear.
- Leaves: Smooth, with cilia at the margins.
- Derivation of Scientific Name: Named after American botanist, George Vasey.
Clammy or Swamp Azalea (Rhododendron viscosum)
- Location: From low elevations up to 5,000 feet, especially near water.
- Form: Multi-stemmed deciduous shrub. Twigs covered with short hairs.
- Flowers: Fragrant white tubular flowers with white stamens and style that extend beyond the petals.
- Leaves: Dark green above and pale green below, turning yellow, orange and purple in fall.
- Derivation of Scientific Name: From viscosus for “sticky”, referring to the stickiness of the corolla tube.
Photography by Ken Borgfeldt, Penny Longhurst, Jim Poling, & Joe Standaert.
Sources:
American Rhododendron Society Massachusetts Chapter – Species in Our Midst
NameThatPlant.com – Rhododendron
Huber, Fred: U.S. Forest Service Plant of the Week: Smooth azalea (Rhododendron arborescens)
Lance, Ron: Woody Plants of the Blue Ridge, p. 27-28, 1994
Swanson, Robert E.: A Field Guide to the Trees and Shrubs of the Southern Appalachians. The Johns Hopkins University Press, p. 304-312, 1994.
Towe, L. Clarence: American Azaleas. Timber Press, 2004.
Weakley, Alan S.: Flora of the Southeastern United States. Edition of 20 October, 2020, p. 1177.
Western Carolina Botanical Club 