Taking the Yak out of Yakushimanum
David G. Leach, Brookville, Pennsylvania
Fig. 1. R. yakushimanum showing broad spreading
plant type, well covered with bloom.
Cecil Smith photo
The interest in R. yakushimanum, both as a garden plant of extraordinary quality, and as a parent of improved hybrids, continues year by year. It is appropriately named in more ways than one. The endless talk about it has produced legend as well as logic, fiction as well as fact, as hobbyists and nurserymen have discussed and praised and criticized various specimens encountered in gardens and professional growers' fields.
It seems that the prime ambition of almost every Rhododendron enthusiast is to own a plant of the form awarded a First Class Certificate ("the F.C.C. form") by the Royal Horticultural Society in 1947. This has been believed to be the finest expression of R. yakushimanum in cultivation.
But the story has been widely circulated in this country, particularly in the East, that the F.C.C. form is at the celebrated Exbury Estate, now owned by Mr. Edmund de Rothschild, and that those who obtained plants propagated from the specimen at the Royal Horticultural Society's garden at Wisley have received instead "the A.M. form," not the F.C.C. form.
Another account, published in the July, 1963 Bulletin, states that "The Wisley plant came from Exbury as a layer from the original plant imported by Rothschild," thus saying in effect that both are the same.
The F. C. C. Form at Wisley There is no such thing as "an A.M. form" of yakushimanum, according to the records of the Royal Horticultural Society, and the F.C.C. form, quite distinct from that at Exbury, is emphatically at Wisley.
Several years after it was described as a new species by T. Nakai in 1921, its extraordinary beauty was recognized by the owner of the Wada nursery in Japan who, in turn, informed his good customer in England, Mr. Lionel de Rothschild, that R. yakushimanum was available for export. The famous Rhododendron connoisseur and breeder immediately sent an order to Mr. Wada and thus brought into cultivation in the western world a species which is an inexhaustible joy in every garden it graces.
Fig. 2. Close up of R. yakushimanum
in full bloom.
Cecil Smith photo
Two specimens of very similar character were grown on at Exbury from the Wada importation, according to the staff and the records at Exbury Estate. Later one of them, which was not a layer, went to the R. H. S. gardens at Wisley, and was subsequently exhibited in 1947 at the great annual Chelsea Flower Show. A faultless mound of burnished convex green leaves glimpsed beneath an almost-solid canopy of fresh pink buds opening to chalk-white flowers, nothing like it had ever been seen before. It was immediately awarded a First Class Certificate. The tens of thousands who visited the show that year were enthralled. It became over-night the sensation of the British gardening world. So great was its appeal that the Royal Horticultural Society exhibited it for several consecutive years, thus whetting the public appetite for plants which were virtually unobtainable.
This, then, is the F. C. C. form. The original plant is at Wisley. It is illustrated in the R. H. S. Rhododendron Yearbook, 1950, and in my own book, Rhododendrons of the World.
But the F. C. C. form is not necessarily the best, and in fact I believe it not to be. The flowers of the Exbury form, which has never received an award, are to my eye more beautiful. They are certainly larger, and are irregularly suffused with a strong, and exceptionally attractive, shade of bright rose, a more emphatic color contrast than is found in the blossoms of the F. C. C. form. The two have much the same convex leaf. Without seeing them growing side by side under identical conditions, it is hard to say which has the better habit of growth.
Having used both the Exbury and the F. C. C. forms in hybridizing, it is obvious that they are quite different genotypes, and here lies the importance of keeping the facts straight. I have crossed both with the same seed parent and the two lots of hybrid seedlings which resulted were distinct. One form produces in some hybrid combinations plants which are much dwarfer than the other. A substantial portion of the seedlings from many yakushimanum crosses, and in a few instances all of the progeny, die at an age corresponding with their first year or two of flowering. Root systems never develop fully and the genetic inadequacies appear to be equivalent to a premature senility.
The hybridist who seeks to capture the characteristics of either the Exbury or the F. C. C. form in combination with the other desired traits may be defeated if the confusion persists between the two. The Exbury form with its fictional Award of Merit shows a much greater tendency to produce hybrids with physiological deficiencies than does the F. C. C. form with its authentic First Class Certificate. Unfortunately, there are in commerce and in private gardens also numerous specimens of R. yakushimanum which are thought by their owners to be the F. C. C. form but which were actually produced from seeds taken from the Wisley plant.
Foliage of Seedlings Quite Variable Self-pollinated seeds from the F. C. C. form produce a wide range of foliage characteristics, varying from the rather long, convex leaf through the wider, flat leaf to an outline that is almost round, and it seems highly dubious that it is possible to separate R. yakushimanum into valid botanical varieties with constant leaf traits, consistent in reproduction. Instead, it seems more plausible to assume that it is an extremely variable species despite its restricted distribution on the little island of Yaku Shima.
Japanese scholars recognize two forms of R. yakushimanum: a form from the lower elevations which has large leaves and blooms with exceptional freedom; and a form from the highest altitudes which has much smaller leaves, more compact habit of growth and is less floriferous. Horticulturally, if not botanically, this distinction may have a limited usefulness. In all studies so far made of apparently different altitudinal Rhododendron forms, intermediates have been found to bridge the two.
It is not true that seedlings with the convex leaves are the finest ornamentally. At least one seedling from the F. C. C. form is much superior to it in foliage, habit of growth, in vigor and quite probably in hardiness as well. From seeds sown in 1950 I obtained a conspicuously desirable plant with handsome, flat leaves and an indumentum so heavy that it coats the stems and forms a farinose veil upon the upper surface of the new leaves as well. It grows considerably more rapidly than the F. C. C. form, yet retains a flawless habit and so it has an important commercial advantage in addition to its aesthetic superiority. The buds are deep pink with a good deal of orange, almost salmon-pink. The first day the open blossoms are clear appleblossom pink, aging thereafter to clean white, with a thick, heavy substance and texture resembling a Calla lily. This specimen was selected in 1958 and given the number 58-1. Some plants were propagated from it and distributed under this number. It has now been named 'Mist Maiden,' a reference to the mist-shrouded mountain peak whence it originated on Yaku Island, and has been given to commercial nurserymen for introduction when they have accumulated sufficient stock. I have no small plants remaining.
Hardy Species from a Southern Island It is an interesting speculation as to why R. yakushimanum is so much hardier than could reasonably be expected. Yaku Shima is south of the main Japanese islands and has a subtropical maritime climate. The mountain peaks at about 6300 feet have recorded a winter low temperature of -5° F. but they are snow covered for nearly half the year. R. yakushimanum appears to be a great deal hardier than R. metternichii, makinoi and degronianum originating nearly a thousand miles farther north in climates much colder. It is so close to R. degronianum botanically that it may be a relict, having persisted on Yaku Island from a more northerly origin following a major climate change in another geologic epoch. Three forms of R. keiskei, thought by the Japanese collector to be distinct, have recently been brought into cultivation from Yaku Shima. One is quite dwarf and blooms when only a few inches high but unfortunately has the palest flowers. It will be especially interesting now to determine whether R. keiskei from this island origin will also be hardier than plants collected from its more northerly distribution.
A Good Parent
As a parent for hybridizing, R. yakushimanum was first reported by British breeders to be worthless in the late 1940's, and as recently as 1960 two prominent English hybridists recorded their adverse opinions in the Rhododendron and Camellia Yearbook of the R. H. S. The original assessment was undoubtedly made in good faith because no noteworthy hybrids bred in this period have appeared. But a few years later, Francis Hanger at the Wisley R. H. S. gardens, Frederick Street, the nursery of John Waterer Sons and Crisp Ltd., this writer and quite probably others unknown to me, produced a number of hybrids of extraordinary quality.
Apparently my own hybrid, (R. catawbiense var. album Glass x R. yakushimanum) 'Great Lakes' was the first yakushimanum hybrid to receive an award on either side of the Atlantic. It was given a "P. A." in 1960. 'Anna H. Hall', 'Spring Frolic' and 'Pink Frosting', all yakushimanum hybrids, were subsequently registered. At about the same time Cecil Smith showed (R. fortunei x yakushimanum) 'Nestucca' at Portland and it also received a Preliminary Award. The Wisley gardens of the Royal Horticultural Society showed ('Pauline' x R. yakushimanum) 'Renoir' in London to win an A. M. in 1961, and in 1962 the same exhibitor also had an Award of Merit for ('Pilgrim' x R. yakushimanum) 'Lady Bowes Lyon'. Inasmuch as Mr. Hanger had made about fifty yakushimanum crosses at Wisley by 1960, it may be assumed that gardeners will benefit a great deal more as his successor makes selections in the years to come. Frederick Street has produced 'Mountain Star' in England from a cross of 'Stanley Davies' with R. yakushimanum, and it has been widely admired.
Back in this country, R. yakushimanum x 'Harvest Moon', exhibited by Bob Comerford, won the Dr. Goodman Cup for the best new American hybrid at the Portland show in 1963. R. yakushimanum x 'Mars', from the same exhibitor, and Cecil Smith's 'Jalisco' x R. yakushimanum are other hybrids of unusual promise.
This review of R. yakushimanum, its introduction, the forms distributed and its record as a parent, has been written after a careful check of the facts both in Japan and in England, and with the aid of American records. Its purpose is to maintain a clear trail back to the original specimens for the benefit of breeders, particularly, and for the interest it may have to others as well.