The Species Situation in the U.S.A.
Where Do We Stand and Where Are We Going?
J. Harold Clarke
Fig.15. A nice specimen of R. rex
showing the striking foliage.
Cecil Smith Photo
Fig. 20. A plant of R. wightii growing in
the garden of Cecil Smith.
Cecil Smith Photo
The general interest in rhododendrons as garden plants is definitely on the increase. Most gardeners who become really interested in rhododendrons sooner or later begin to give attention to the species, for their intrinsic garden value, their great variety, and their varied charm.
The number of those who are doing some breeding work with rhododendrons is not known but it is larger than most of us realize and increasing. Most rhododendron breeders either start by making crosses between species, or eventually come to the use of species to introduce certain qualities into their breeding lines. For a breeder to contemplate the tremendous number of rhododendron species and simply calculate the possibilities still unexplored of straight inter-specific crosses is to open up a tremendous but frustrating field. He may read the species description in various books, and lay out a wonderful breeding program on paper, but when it comes to carrying it out he must have a true form of the species.
A Thousand Species
We sometimes say that there are close to a thousand species in this tremendous genus, and that is reasonably true if we include the tropical as well as temperate zone species. Probably there will be more merging of species by the taxonomists, but additional ones will be located if exploring and collecting in the Western China area again become possible. Even when species are merged, with one becoming a botanical variety, there are usually differences, of interest to the gardener and to the breeder. Beyond that there is ample evidence that different clones within a species may have quite different breeding potentials. One of the classic examples is the Loderi group, resulting from the same cross, but with different parental clones, which produced the earlier but less spectacular 'Kewense'. The recent article by David Leach on R. yakushimanum stresses the different breeding qualities of two clones with little in the way of distinguishing characters visible to the eye.
A Century of Cultivation
The history of the discovery, and introduction into England, of many of the rhododendron species has become reasonably familiar to most fanciers. The names of Hooker, Forrest, Kingdon-Ward, Rock and others are part of a romantic and to many of us a remote background. Certain species, as R. catawbiense and R. arboreum, were introduced into England over 150 years ago and it probably would be true to say that most of our better species were introduced to cultivation between 50 and 100 years ago.
Plant material sent back to England by the great plant explorers was, in general, consigned to the botanic gardens at Kew and Edinburgh, and to the private gardens of a few wealthy estate owners who supported, in whole or in part, the expeditions which did the collecting.
In the British Isles there may be half a dozen really extensive rhododendron species collections in public gardens, such as the Botanic Gardens and Windsor Great Park. There are a few great private collections and a limited number of small private collections, some noted more for the size and excellence of individual plants than the number of species. A very few nurseries list rhododendron species and, for the most part, they are open pollinated seedlings which will exhibit the normal seedling variation resulting from bee pollination.
Few Large Collections In This Country In the United States there are a few Botanic Gardens and Arboretums which have collections of rhododendron species. Most of these are rather limited, partly because of climatic conditions in their particular locations, and partly because the rhododendrons comprise but one of many plant groups which the Botanic Garden feels are necessary in its program.
There are a few good private collections, but in terms of total number of rhododendron species in existence they are mostly very incomplete. A very few nurseries offer rhododendrons as named species and a large part of those offered are seedlings, although a few nurseries are making selections and offering clonal material. The number of selected rhododendron species clones generally available in the nursery trade is certainly very small. At the same time the demand is constantly increasing, not only from collectors but also from landscape architects who are more and more coming to realize the esthetic value of many of the species.
It has been the experience, in both American agriculture and American gardening, that more or less continuous plant breeding has been found desirable and has resulted in greatly improved varieties. With 10,000 hybrids and 1,000 species to be considered as parents there would seem to be enough possibilities for the most ardent breeder. When we consider what has been done by plant breeders in other genera, where there may have been only two or three, or possibly a dozen, species to begin with the potential for rhododendrons seems quite unlimited.
The Present Situation
Since the American Rhododendron Society was founded, in 1944, interest in breeding has been moving rapidly. Test and Display Gardens have been established, and in general the appetite of the gardening public for new rhododendron material has been stimulated. However, not a great deal in the way of new foundation breeding material has become available during that time.
The fact is that the average member of the Society has little chance of obtaining propagating material of species, aside from a few offered in this country. Perhaps 200 to 300, of the better known species are available, mostly as seedlings. and in many cases relatively unselected and unproven as to specific identity. It must be remember. ed that, with some species, it takes many years to grow a plant to blooming size so that it can be identified with reasonable accuracy. The primary source of the species being offered in this country has been seed obtained from the Botanic Gardens or, in some cases, private collections, in the British Isles.
The A.R.S. Species Project
For the last two or three years the American Rhododendron Society has had a Species Project which has been outlined from time to time in the Bulletin. The Species Committee has been attempting to find, in the Northwest so far, plants of certain species which can be reasonably accurately identified as true to name. Since most of the flowering size rhododendron species plants in our gardens are seedlings, it is inevitable that there will be a fair number that are not true to name, that is, they may be some other species, or they may be hybrids. They may be beautiful and valuable garden plants but it certainly is desirable to know their true identity. The Species Project has the further objective of finding one or more superior forms of each species being studied with the hope that these may be propagated asexually and eventually become available to the gardening public. Since these plants are usually in private gardens the owners may not be particularly interested in having their plants cut for propagating material. However, in most cases the owners would probably be willing to have one or two propagators take cuttings so that eventually the clone would be increased and made available to other gardeners.
The progress made by the Committee has been indicated by recent discussions in the Bulletin of certain outstanding clones of a very few species. The Committee decided at the beginning to actually study only a few species at a time in order to avoid complete scattering of effort. Several dozen species have been studied but so far only a dozen or so species have been reported on.
As the species first studied were reasonably well known and readily available it is evident that to cover any large portion of the total list of species would be a tremendous task and one requiring generations of time and effort. Furthermore only a fraction of the total number of rhododendron species is now established where it can be studied by the Committee.
The Windsor Great Park Collection
In the late summer of 1963, Dr. Milton Walker, Chairman of the Species Project Committee, visited Windsor Great Park, a part of the Crown Estate not far from London. There he saw the famed Stevenson collection of rhododendron species plants. This collection, started in 1918 by Mr. J. B. Stevenson of Tower Court, Ascot, developed into one of the great species collections of the world. Mr. Stevenson served as Editor of the book "The Species of Rhododendron" published in 1930, and of course this collection formed the basis of much of his knowledge about species. When he died in 1950, a large part of the collection was purchased by the Crown Commissioners and transferred to Windsor Great Park. There it has been displayed on some thirty-five acres of rolling ground where the plants apparently have thrived, encouraged by being set far enough apart so that their typical form can develop without crowding. Roughly there are some 460 species represented by over 2,000 clonal forms. In many cases these forms represent collections by different explorers in different parts of the world.
Dr. Walker was struck by the thought that his Committee could work for many years and never find a fraction as many good clonal forms of species as were growing in this one magnificent collection. Here were practically all of the available rhododendron species, and in many cases with several very good forms, and all verified by Dr. Fletcher and Mr. Davidian of Edinburgh. If propagating material from all these forms at Windsor Park, as well as from Edinburgh, and other sources, could just be sent to the United States and established at an appropriate site it would represent about the greatest possible step in making typical and superior forms of the greatest possible number of rhododendron species available to American breeders and gardeners.
Excellent Cooperation Found
Contact was made with Sir Eric Savill who was in charge of the planning and development of this garden and its subsequent maintenance, and with Mr. Patrick Synge, Editor of the Royal Horticultural Society. A conference involving Dr. Walker with these gentlemen and with Mr. Findlay, who is in direct charge of the Windsor Park collection, found them all extremely cooperative and willing to do whatever they could to provide propagating material for the establishment of a large collection in the United States, under the auspices of the Species Project Committee.
It was brought out that there are superior species forms in many private gardens in Great Britain, most of which are known to Sir Eric and Mr. Synge. Dr. Walker was promised that access to these gardens could be arranged, and that every effort would be made to facilitate the obtaining of propagating material from them. He was invited to return early the following spring, and actually see as much as possible of these forms at Windsor Great Park and other places during the blooming season. Dr. Walker arranged to do just that and Dr. and Mrs. Walker departed this country for London on March 18.
It seems, therefore, that the best rhododendron species forms now growing in Great Britain, the result of a century and a half of plant exploration, and selection, are potentially available to the American public.