Native Eastern Azaleas
By David G. Leach
Condensation of a talk given at the fifteenth Annual Meeting of the American Rhododendron Society
at Portland on May 9th, and at a meeting of the Seattle Chapter on May 21st.
To an underprivileged eastern enthusiast the advice to "Go West" refers not to gold, or to business opportunity, but to the rhododendrons of the Pacific Coast where the genus displays its attractions in a variety and magnificence unknown in the northeastern United States. We Easterners think of ourselves as poverty-stricken in the rhododendron resources available in our climate, but in deciduous azaleas, at least, our part of the country is the richest in the world.
Of the 18 species in the Luteum subseries all but three are native to the East and we have as a bonus two species in the Canadense subseries. Most of them are fine ornamentals which have been rather badly neglected. The few representatives of our native eastern species which I have seen in the Pacific Northwest are almost all inferior forms, far less attractive than the best that this fine group can offer. For that matter, most of the gardens in the East do not exhibit a great deal of discrimination between the undistinguished average and the exceptionally superior, which is the normal ornamental range to be found in all of the native Azalea species.
Deciduous azaleas are highly evolved rhododendrons, the end product of a long line of ancestors that began with the Magnolias and continued through the Camellias into their most primitive forebears in the genus, the Stamineum series. With the imperceptible tide of geologic ages the Ovatum Rhododendron group was formed, then the Albiflorum series and finally the Canadense type of azalea made its appearance on earth. The Obtusum group descended next, and from it came the deciduous azaleas of the Luteum subseries as we know them today. The evidence for such a family tree is persuasive. The native American azaleas are of ancient lineage, among the aristocrats of rhododendrons in the length of their patrician pedigrees.
But like many aristocrats they are all related, sometimes a little too closely for the convenience of those interested in unraveling their ancestry. The eastern azaleas are, for the most part, not at all well defined. There has been an enormous amount of crossing in the wild. In some locations in the North Carolina mountains it is often hard to find a typical specimen with the classic characteristics of its species amid the welter of natural hybrids. Man has hastened the appearance of vast numbers of these hybrids by clearing the land, burning over scrub areas, making roads and otherwise creating new ecological niches into which nature's hybrids can fit at a selective advantage. In fact, it seems that the natural hybrids spring up almost unfailingly to exploit the new environment.
I find it easiest to keep in mind the native Azaleas by classifying them in color groups: the early whites (alabamense, atlanticum); the early mid-season pinks (canescens, nudiflorum, roseum); the species in the red-yellow-orange group (austrinum, speciosum, calendulaceum, bakeri, prunifolium); and the late whites (arborescens, viscosum, oblongifolium, serrulatum).
Taking them in this sequence, alabamense is a rare species which is found only in the central part of northern Alabama. It is a little Azalea of convenient height, not often more than four feet tall, which blooms rather early in the total sequence of eastern Azalea flowering. It is usually described as stoloniferous but the plants in my garden have not been so and those I have seen in the wild can safely be said to be much less strongly stoloniferous that the impression that would be gained by applying that term to atlanticum, for example. Good forms of alabamense, with broad corolla lobes, make handsome shafts of white in the forefront of an azalea planting. The easiest way to identify this species is by crushing the foliage. The definitive jasmine or lemon scent in combination with white flowers similarly fragrant is usually reliable in identifying R. alabamense. But if the blossoms are pale pink, the plant comes from a natural cross with canescens, a species with which it is much too familiar.
The other "early" white is atlanticum, closely related to alabamense, but with a distribution ranging from southern Pennsylvania to South Carolina. It too is a low growing azalea and strongly stoloniferous, forming colonies as much as 25 feet across and probably could be demonstrated to spread even farther if anyone cared to determine the limits of a single plant by untangling it from a large stand. A young plant is apt to be a little diffuse in its ornamental effect, with a cluster of flowers atop each stem about 20 inches high, but when a sizable clump has been formed this species is extremely effective as a dwarf Azalea in the garden. Unfortunately, it is rare to find atlanticum in its typical form. I have seen it so only along the Seaboard Railway line near the northern border of North Carolina. Dr. Henry Skinner found the type also on the Delmarva Peninsula of Delaware. An easy identification can usually be made by the five rows of stalked glands near the tip of the dormant floral bud, but there are plants in southeastern Pennsylvania six feet tall which correspond in every botanical detail with atlanticum. Such giants, and smaller plants with pink flowers, are usually the result of natural hybridization with canescens in the South, or with nudiflorum in the North.
In the pink flowered group of native azaleas, R. canescens comes into blossom first. It reaches up to 15 feet as it is found from North Carolina to Florida and westward into Texas, and I think it has been a little maligned as a garden decoration. The usual comment in books is that the same ornamental effect of canescens can be obtained by roseum or nudiflorum, which are hardier and generally superior. The trouble is that they do not bloom at the same season, canescens flowering a good deal earlier, at least in my garden, and in any case the finest forms of canescens are absolutely first rate, free blooming and effective garden shrubs. The rare and appealing salmon pinks are not duplicated in the northern species, either. I will concede only that the average quality of canescens for cultivation is below that of its northern relatives.
This species blooms along the edge of woodlands in late March in southern Georgia where it often catches the eye of tourists homebound from Florida. The flower color is apt to be pale and undistinguished, the blossoms rather small and somewhat crumpled, unless superior forms are sought and then the more northern distribution areas, especially, produce some handsome plants.
In the pink-flowered class of eastern native azaleas R. nudiflorum follows next in bloom, usually a tall, vigorous shrub which grows in the wild from Massachusetts to North Carolina and westward into Missouri. Books often erroneously give its western limit of distribution as Ohio. The good forms of nudiflorum are remarkably fine ornamentals, free flowering and easy to please, covering themselves with a pale to deep pink blanket of blossoms. The poor forms tend to have twisted flower lobes and rather small blossoms of pallid color, which may have a somewhat wrinkled appearance. The classic quick distinction from roseum is based on scent, nudiflorum having a sweet fragrance and its near relative a clove-like, spicy one. I find it a good deal easier to distinguish the two on the basis of their hairy character, nudiflorum being essentially without hairs on the dormant floral buds and roseum with hairs. In Pennsylvania, at least, nudiflorum tends to be found at lower elevations and roseum farther up the mountains. These two are often confused and I have even seen one of the species labeled with the name of the other at one of the great flower shows in London.
These two species are reported to interbreed freely but in our part of the state, where myriads of both can be found, natural hybrids are not common. They are pretty well confined to narrow zones where the nudiflorum on the lower slopes overlap the roseum coming down from the higher.
Roseum, which blooms at the same time, appears to be the more primitive of these two and must be credited with being superior on the average. It is found from New England to Virginia and westward into Indiana with pink flowers, some so pale they are almost white and others so deep they are almost red. I think the best forms are among the finest ornamental plants in existence, with a beauty surpassing any of the modern commercial azalea hybrids.
It seems to me that many rhododendron hobbyists have become overly preoccupied with large flowers, often forgetting that a profusion of smaller blossoms may actually be more colorful than bigger blooms borne in clusters farther apart. In addition, there is in this and other Azalea species a natural beauty arising from the subtle balance between size of flower and leaf and in their proportions as related to the structure of the branches. Here is a perfect integration of plant architecture which has the clean and natural unity of nature's art. There is a high standard of easy grace and distinction which often seem lacking in many of the modern commercial hybrids. Both have their attractions but my plea is that we not overlook the virtues of the species. There is plenty of room for them too, not as botanical curiosities, but for their colorful contributions as fine garden plants. R. roseum in its best forms qualifies on every score.
R. austrinum is the first azalea in the red-yellow-orange group to bloom. It seems to be a primitive ancestor of the well known Flame Azalea, R. calendulaceum. In its typical form it is not much as an ornamental, because its pale yellow flowers with reddish stripes outside are rather small and spidery in effect. This is the common average of the species as seen in the lowlands of Georgia and Alabama, with a few in northern Florida. But R. austrinum also occurs with larger, handsome orange or clear yellow flowers, many in a cluster, and then it is a striking plant in the garden, blooming before this color range is available from any other deciduous azalea. It is an upright shrub of medium size, and very glandular.
Next to bloom in the red to yellow group is R. speciosum, a non-glandular species which offers some of the finest colors to be found among the deciduous azaleas. No hybrid I have yet seen equals the incandescent reds, the luminous yellows and soft pastel blends of superior forms found in the lowlands of Georgia and South Carolina where this species is native. Speciosum is most often a shrub six or seven feet tall. It is very free blooming in cultivation, the flowers mantling the plants in a cloak more colorful than the fewer, larger blossoms of the newest commercial hybrids. Natural hybrids with canescens are easy to find in the wilderness and they are often stunning in their flowering effect, blanketed with pale to vivid pink flowers. Speciosum is easily distinguished from calendulaceum because it is essentially non-glandular whereas the latter is glandular. The text books fail to mention that it is also usually less vigorous and has an entirely different appearance, being lighter in texture, a little smaller in leaf and thinner in branch so that it has a more delicate, graceful character.
R. calendulaceum has been recognized for generations as a fine ornamental but the very best forms are rarely seen in cultivation. This species seems to have descended from the early blooming austrinum and the late-blooming prunifolium, and to have inherited the finest traits of each. It is an upland Azalea, found at the higher elevations from Pennsylvania to Georgia, and the greater the altitude the deeper the color is apt to be. Unfortunately, the brilliant reds usually fade when the plants are dug and taken to gardens at lower elevations. But the yellows and oranges are often extraordinarily effective and in some fine forms the blossoms are borne in globular trusses with a halo of exerted stamens distinguishing them. The forms with apricot colored blooms are exceptionally appealing.
This is the best known of the eastern Azalea species, a tall, vigorous shrub to ten or twelve feet-some times more. It is hard to find a really poor specimen but one of the finest gardens in the East features one, with undersize flowers of nondescript color. The so-called "pink calendulaceum" and "white calendulaceum" are the result of a traveling salesman bee having been entertained by an arborescens.
A few years ago I was taken, with several others, to a site near Burning Town Gap by Dr. W. N. Fortescue where we came across a stand of calendulaceum, with giant clear orange flowers marked by a bold golden shield on the upper lobe. The blossoms were about two and a half times larger than the average for the species, almost oriental in their brilliance. This remarkable find points up the importance of obtaining the very best forms for garden use of the immensely variable deciduous azalea species.
R. bakeri can best be described in its ornamental effect as a superior, later blooming calendulaceum. It seems to me to be a finer species because it is more compact in growth, not often over six feet in height, and it holds its foliage in good condition right to the end of the season. Its season of bloom, late June, is exceptionally valuable and its color range in the garden includes not only yellows and oranges but also remarkable, electric reds which retain their brilliance when the plants are grown at low altitudes. More of the fine forms bear clearly defined trusses of many flowers.
Where bakeri and calendulaceum occur at different altitudes so that their blooming seasons overlap, vast numbers of natural hybrids between the two are found. Offspring of crosses with arborescens in the wild are frequently striking and unusual pink shades, highly effective for garden use.
Some years ago I had about sixty plants of Dr. Braun's cumberlandense collected for me southwest of Cumberland, Kentucky. These have developed into a phenomenal group of azaleas, all of outstanding garden quality, and have become the principal display feature of my garden in late June. I think they may be unique in cultivation and I have distributed seeds freely to botanical gardens, nurseries and amateur enthusiasts.
It has been suggested that cumberlandense should be submerged in bakeri, there being not sufficient distinction to warrant two separate species. This particular group of cumberlandense, at least, has a different character and habit of growth than any bakeri that I grow or that I have seen elsewhere. They range from clear orange to blazing scarlet, with the great majority in brilliant red shades, the flowers well presented and forming great masses of color. These are far superior to "Camp's Red." I have not made a minute botanical comparison of the plants in this group with bakeri but I am confident that there now exist many rhododendron species with less difference between them than that between bakeri and cumberlandense as I know it from my own plants.
The last to bloom of the yellow-orange-red group is R. prunifolium, a rare lowland species from a limited area along the Georgia-Alabama border which grows as much as fifteen feet tall. This azalea received a First Class Certificate from the Royal Horticultural Society and it is certainly extremely valuable for garden decoration, flowering in August or even September when color from woody shrubs is at a premium. Orange and yellow flowers are seen occasionally but the blossoms are usually red, and the best forms are a vibrant red which shines out brilliantly in the landscape. When I scouted this species in the wild it seemed to me to prefer low spots and shallow valleys, possibly indicating a preference for more moisture. Since it comes from such a limited geographic area its hardiness could be expected not to vary much, but some plants in my cold garden appear to be a good deal more bud-hardy than others.
Turning now to the late whites, arborescens, viscosum and oblongifolium bloom at about the same time, early July, in my garden, with serrulatum following much later, in early August. In the wild they vary a good deal in every respect and the first three cross at every opportunity with any other Azaleas nearby. All are fragrant. Oblongifolium, which comes from Arkansas, Texas and Oklahoma, seems to offer nothing unique as a garden plant. Arborescens is probably superior to viscosum on the average, and in its finest forms is an extremely valuable azalea for its immaculate cool white flowers coming just as the hot weather begins. The flowers are hidden by new growth on poor forms, and may have either undersize blossoms or narrow carolla lobes reducing their effectiveness. In age arborescens becomes a very large, spreading shrub and then it can be one of the stars of the genus, its white flowers shining out in bold display against a background of glossy foliage, scenting the garden for a long distance. Its natural hybrids resulting from repeated back-crosses from bakeri in the wild are often phenomenally beautiful in pastel pink and ivory shades and in white.
Arborescens has smooth branchlets and those of viscosum are bristly. If you have a late white azalea species and are wondering which it is, that is an easy way to tell the difference. Arborescens occurs from New York to Alabama, viscosum from Maine to South Carolina, and where they overlap they interbreed freely. In the Northeast viscosum is usually found near water but it grows well in any average garden soil and varies a great deal in stature, from dwarf and stoloniferous to large and upright. The best forms seem to be intermediate in stature, vertical in growth habit and to have flowers with shorter tubes, more abruptly dilated, which are freely borne in a forward position so that they are not hidden by the new growth. It blooms about the same time as bakeri and its blue-green foliage makes a pleasant contrast.
R. serrulatum is the latest blooming rhododendron in the entire genus. This azalea can be found in flower in central Florida in early November. It is similar to viscosum but not quite so decorative, usually. Its white flowers with long tubes are an interesting note in the northern garden in August.
Turning now to the two eastern species in the Canadense subseries we have canadense itself coming into flower early in the season, long before the azaleas of the Luteum group make their contribution. This is the azalea beloved by poets, the Rhodora, a neat little dwarf with grayish green foliage about three feet tall which spreads by underground stolons and soon forms a satisfying clump bearing many small lavender-rose blossoms atop the naked stems. I am especially fond of forma albiflorum, with white flowers, which is the first to usher in the Azalea blooming season each year. R. canadense extends its natural range from Labrador and Newfoundland to northern New Jersey. In the garden it wants a more acid soil than the other Azaleas to really thrive.
R. vaseyi blooms only a little later than canadense and I count it among the finest of all azaleas, but it is extremely variable in its ornamental value. I have some plants with flowers twice the size of others. The blossoms may be undistinguished pallid pink or they may be, in the wilderness, a velvety crimson which becomes a deep, rich pink in gardens at lower elevations. There is a stunning white with large flowers called 'White Find', introduced by LaBars' Rhododendron Nursery at Stroudsburg, Pa. This, inter-planted with the deep pink form, makes a woodland scene of remarkable distinction, the flowers poised on the branch tips like swarming butterflies so early in the season.
Vaseyi comes from the mountains of North Carolina. It makes an upright, tall shrub 12 feet tall in old specimens, with an oddly light and graceful appearance in bloom. It is highly regarded in Europe and sadly neglected in this country. I have never succeeded in crossing it with any other azalea, even canadense in its own subseries.
With the eastern natives making their contribution, azaleas can be in bloom in our gardens from early spring to early fall, months before and months after the commercial hybrids put on their annual show. But the difference between the best and the poorest in each species is often the difference between platinum and tin. The finest expressions of the species are gradually being propagated by progressive nurserymen as the rooting of soft cuttings becomes routine. The day may not be too distant when these remarkably decorative plants will be known by their outstanding representatives, and recognized everywhere for the important part they can play in our gardens.