Rhododendron occidentale - One Species or Many?
Frank D. Mossman, M.D., and Britt M. Smith
While preparing for this presentation, we wondered about the total group of native American azaleas. Reference is made to the publication distributed by Callaway Gardens, "'Native and Some Introduced Azaleas for Southern Gardens" by Mr. Fred Galle. This treatise lists fifteen species which are native to the Eastern portion of the United States. These fifteen species grow from Maine to Texas, generally near the Atlantic Ocean and the Gulf of Mexico. They vary from white to yellow, to orange, to red, and some are fragrant. Most grow in areas of high humidity and/or damp soil. We from the West Coast envy you that variety and the tremendous interest which it could foster. In the Western United States we have only one azalea, R. occidentale, and two rhododendrons which are not azaleas, R. macrophyllum R. albiflorum. We are pleased though when we contemplate showing our pictures of R. occidentale to you, especially when we think that we will be able to show you nearly as much variation in our one species as you have in fifteen! If this is a challenge to you, please accept it as a friendly one. It would please us greatly if it is challenge enough to motivate someone to investigate any or all of your species as we have investigated R. occidentale. We may be grossly in error, misled by the extreme variation we have found in one species, but we believe that there are outstanding specimens of each of your Eastern native species not yet publicized or seen on the market. If someone knows, or finds such an outstanding plant, we hope that he will propagate it and make it possible for us to have it in our collection.
Before we leave generalizations entirely, may we suggest that you, with your knowledge of the beautiful native species in your area, attempt two things as you see the slides:
1. Produce a botanical description of R. occidentale.
2. Consider, as others have done, whether R. occidentale all belong in one species.
To be complete, this presentation must mention the work of Mr. Leonard Frisbie, which is the basis for all of our effort. Mr. Frisbie, of Tacoma, Washington, published a report of his work in the January, 1961, issue of "Rhododendron", the organ of the Pacific Rhododendron Society. This report was the culmination of nine years of intensive investigation involving correspondence with and visits to a number of universities in Oregon and California, numerous trips to the lands of R. occidentale, traveling by bus and on foot, and return trips during the winter to collect plants which he had marked during the blooming season. This was an excellent and commendable effort by a dedicated man who overcame many obstacles and inconveniences to collect the first substantial body of information about a remarkably variable and beautiful species.
Rhododendron occidentale is native to the area from approximately one hundred miles north of the Oregon-California border to the Mexican border. East and west, it grows generally from the ocean shore to the Cascade Mountain Range and Sierra Nevada Range. Our explorations have been limited to an area roughly bounded by lines drawn between Roseburg, Coos Bay, and Grants Pass in Oregon, and Crescent City in California, and on down the coastal region approximately one hundred miles to Arcata, California.
R. occidentale seems to cling to tradition with regard to its habitat. It prefers to grow where the soil is moist and acid, and where the relative humidity is high. Where there is fog along the ocean shore and where conditions produce the high relative humidity, it prefers to grow in an exposed situation. Where the humidity becomes low during the warm part of the day, it seeks partial shade. Flowers attain their most vivid coloring in full sun, and the plants are most floriferous in full sun where we find them, so we are convinced that along the coast they like all the available sun, This, again, depends upon relative humidity. R. occidentale may be different from other azaleas in this respect: We find them growing where their entire root system is under water. Some plants have been dug from soil which is so wet that the hole fills with water as soon as the plant is removed. This is always, it seems where the ground slopes and the water must be moving rather rapidly. If water-logging of the soil occurs only in winter, they will grow where the ground is flat.
Plants growing in particularly moist conditions have very compact root systems. We are able to dig a plant six feet high and as large in diameter, and load it into a wheelbarrow virtually without disturbing the roots. Plants growing in a relatively dry situation have a compact root system, but will in addition have one or more tap roots emerging from the bottom of this system to go down for water. We transplant these plants successfully by severing these tap roots, and have no idea how deep those tap roots may go.
Fall colors of R. occidentale leaves may be anything from yellow to scarlet to blue. Some plants drop their leaves in autumn while they are still green. There seems to be as much variation in this and other characteristics of leaves as there is of the flowers. Some are light green; some few tend toward yellow; some are rich, dark green; some are shiny and waxy looking; some are matte and deeply veined. Thickness of the leaves varies, as does thickness or fleshiness of the flower petals.
During the winter, the dormant flower buds vary from light green to deep rusty brown in color, and from long, slender and pointed to almost spherical in shape. Again, sunlight is a factor in bud color, but each plant has its own basic bud color and form. Seed pods are usually sausage shaped, but one plant has seed pods more the shape of a hazel nut.
But what about the flowers? The first R. occidentale which one might approach in its native habitat could be expected to conform to the description taken from the "Rhododendron Handbook". "Deciduous shrub up to ten feet. Leaves up to 3½ inches long and 1¼ inches broad, elliptic to oblong lanceolate, changing to yellow, scarlet and crimson in the autumn. Flowers usually expanding with the leaves, in trusses of 6-12, up to 3 inches across, broad funnel-shaped with gradually flaring tube, creamy white to pale pink, often pinkish on the corolla reverse, with pale yellow to orange yellow blotch, sweetly scented." There are thousands of shrubs to which this description would apply. But R. occidentale do not read the book, and they vary much more than the description would lead one to believe.
Unless it had some other very unusual characteristic, we would not catalog a R. occidentale which conforms to the description. Many of our collections have 20 to 25 florets per truss. One small plant had 49 florets per truss. One plant has florets consistently 4 inches across.
Two hints are offered for rhododendron hunters and photographers. (1) You have not adequately checked a plant until you have held the florets in your hand. We have walked within five or six feet of some of our best specimens several times before we finally stopped to inspect them. (2) You can neither see nor photograph the color of flowers in full sun - inspect them in your shadow and photograph them in the shade. We carry white nylon umbrellas to make a light shadow.
The pictures are presented to you in the order in which we found them. Those which were catalogued are numbered SM #1 through SM #63, for those found during the 1966 blooming season; SM #101 through SM #190, for those found during the 1967 blooming season; and SM #201 through SM #258 for those found during the 1968 blooming season. Some which we thought nice enough to collect but not good enough to catalog, we have given "DD" number. "DD" means dig dig. and that in turn means to dig that plant in the fall. To some we have given pet names, such as "New Look" or "Stage Coach Cream" or "Siamese", which we will explain when we come to the pictures.