JARS 43n2 - Corolla Variations In The Flame Azalea

Corolla Variations In The Flame Azalea
L. Clarence Towe
Walhalla, South Carolina

The Flame Azalea, Rhododendron calendulaceum , with its large flowers ranging from canary yellow through the oranges to the true reds, is probably our most widely recognized native azalea. In addition to its color variations, it also has the added attraction of having a wide range of corolla shapes. Probably most species of rhododendrons exhibit atypical corollas, but the Flame Azalea seems to have a predisposition to the unusual.
In addition to the typical corolla, the atypical shapes seem to fall within five basic categories, though other shapes have undoubtedly been observed. Possibly the rarest is the apetala form, whereby all petals are missing, having been replaced by extra filaments. The overall effect is somewhat like an artist's brush.

R. calendulaceum 'Cullowhee', apetala form.
R. calendulaceum 'Cullowhee', apetala form.
Photo by L. Clarence Towe

The polypetala form is unusual in that the five fused petals of a normal corolla are split to the base. Each petal is narrow, strap-shaped and not attached to the other four.

R. calendulaceum, polypetala
R. calendulaceum , polypetala
Photo by L. Clarence Towe

The tubiform type (probably not a valid term) consists of a tube only, with the corolla missing where the flare begins. The semi-double form is fairly common and consists of petaloid filaments in various expressions.
The last category is the full double, whereby all filaments have been replaced by full petals. The pistil may or may not be present.
The causes of these variations may be attributed to two possibilities. First, these variations may simply represent random mutations of a much wider range to be found within the species.
Secondly, these forms may be natural tetraploid x diploid hybrids involving Rhododendron periclymenoides , the Pinxter Azalea. The evidence for this possibility lies with the fact that these unusual forms are most often found in areas known to contain hybrids and many of the hybrids as well as the mutant corolla forms are sterile. Other evidence indicates the mutant corollas may be only one symptom of a much broader syndrome commonly observed in natural hybrids. Such abnormalities may include narrow, elongated buds, flowering prior to or after leaf emergence, extremely wide or narrow leaves, some with twisted and/or bullate surfaces, dwarfness or vigor, brittle or difficult-to-break wood and a host of more subtle differences.
Unfortunately, most plants possessing the unusual corollas do not exhibit the trait uniformly and many of the forms are not at all attractive. However, some of them are fertile and may have some value in breeding or as collector's items.

Clarence Towe, Southeastern Chapter member, is a amateur botanist who collects both species and natural hybrid azaleas in Georgia, North and South Carolina. He is employed as an administrator with the Oconee School District.