The Hybrids of Oconee
L. Clarence Towe
Walhalla, South Carolina
Oconee County in northwestern South Carolina seems to be an ideal location for the occurrence of hybrid swarms of native azaleas. The primary reason for this is that the area is in the transition zone between the northern Piedmont and the lower reaches of the Blue Ridge Front. The Flame Azalea, R. calendulaceum, inhabits the southern Blue Ridge Mountains from well over 5,000 feet in elevation, down to perhaps 600 feet in elevation in certain microclimates in the upper Piedmont. The Pinxter Azalea, R. periclymenoides, usually does not occur above 3,500 feet in our area and is primarily a northern Piedmont species found at elevations as low as 500 feet.
This transition zone between the foothills and the mountains occurs in several counties in northern Georgia, South Carolina and North Carolina, and perhaps in other states. The overlap of the two species generally follows a northeast-southwest path along the southern slope of the Appalachians. Other species, such as R. canescens, R. arborescens and R. viscosum var. montanum, occur in certain areas in Oconee, but there is no evidence that they are involved in the hybridization. Why these two species hybridize so freely is somewhat of a puzzle in that the Pinxter is adiploid (2n = 26) and the Flame is atetraploid (2n = 52). Seedlings of such parentage would be expected to be sterile triploids (2n = 39), and indeed some of these hybrids are totally or nearly sterile. There may be two possible explanations as to the fertility of the hybrids. One may be that all Flame Azaleas are not tetraploids. Many plants that appear to be non-hybrid Flames are typical yellows, oranges and reds, but have flowers smaller than would be expected of that species. Another explanation, given by Dr. August Kehr in Fred Galle's book Azaleas, is that diploid egg cells or pollen cells act as functional tetraploids when crossed with tetraploids, resulting in fertile tetraploid seedlings. Whatever the genetics may be, the two species have found mechanisms to bypass their supposed incompatibility. To describe a typical hybrid involving these two species is difficult. As the Pinxters finish flowering, very early oranges begin to appear which, when examined closely, usually open with two narrow bottom petals and a pink flush which may disappear or intensify. The narrow petals are typical of the Pinxter, and other than for a few inconspicuous traits, the plants could easily pass for Flames ('Sundance Yellow' - compact - slight fragrance). The Flame apparently has the abilities to mask many characteristics of the Pinxter. The conspicuous hybrids, the ones the collectors are primarily interested in, are easy to recognize. The flowers may be large or small, but will usually be bright pink or rose, typically with an orange or yellow blotch ('Rosebeam'). Most are non-fragrant but some may be mildly fragrant. The plants may be low and stoloniferous or may be ten feet tall. Some pinks and roses are so bright as to be described as 'fluorescent' and can be quite attractive. Some flowers will not have the blotch and may vary from yellow to red, but usually with one or more distinguishing traits, such as burgundy pistils and filaments ('Nova') or a blend of colors with a net-vein overlay of a contrasting color ('Chickasaw'). Other flowers are delicate pastel blends of pink and yellow or orange ('Issaqueena'). Some of the flowers go through color changes, usually beginning light and darkening after a day or so. This is generally not a desirable trait, but in some forms the change is so dramatic that it is of interest.
Photo by L. Clarence Towe
Hybridization between these two species apparently affects leaves as well as corollas. Wide leaves with bullate surfaces or narrow leaves with twisted margins are common. Leaf thickness is usually increased, and leaf color can vary from very light to extremely dark. Some leaves are smooth while others are coarse and hairy. Corolla shapes are apparently affected also, in that apetalas, strap-petals, semi-doubles and other variations are frequently encountered. Most are novelties and are sterile due to fasdated or split styles. Usually these traits are not uniformly expressed on the shrubs and may vary from year to year. In that most of the hybrids have wide petals similar to those of the Flame Azalea, that trait may be dominant. The typical Pinxter has narrow petals with revolute margins giving it a rather ragged look and is distracting, even in the better color forms.
Photo by L. Clarence Towe
While truly unique forms are not as common as with the R. arborescens x R. bakeri hybrids of the higher elevations, these hybrids seem to retain their color when moved. High elevation hybrids usually lighten somewhat when moved from 5,000 feet to 1,000 feet. By crossing similarly colored forms (such as rose with yellow blotch x pink with orange blotch), the time it takes to produce seedlings of a particular color range can be decreased. To cross a typical Pinxter and a Flame to get something unusual will probably result in inferior plants, especially in the first generation. If hybridizing is of interest and natural hybrids are not available locally, a deep rose or pink form of the Pinxter crossed with a deep red Flame will increase the chances for bright, blotched seedlings.
It should be noted that Oconee County, South Carolina, is located some 100 miles to the north of the range of the Oconee Azalea (R. flammeum). The Oconee Azalea is reported to be named after the Oconee River in mid-Georgia and, while having some characteristics of the Flame Azalea, is an entirely different species. Oconee is a Cherokee word used frequently in the Southeast and has caused some confusion with respect to the Flame Azalea found in northern South Carolina.
Clarence Towe, Southeastern Chapter member, is an amateur botanist who collects species and natural hybrids in Georgia and the Carolinas. He is employed as an administrator with the School District of Oconee County.