R. Yakushimanum and its Home, Yaku Shima
By A. F. Serbin, M.D., Hartford, Conn.
The great Japanese botanist T. Nakai first described R. yakusimanum (or more properly, "yakushimanum") in 1920. Very little is found in the world's literature regarding R. yakushimanum except in the Japanese writings describing the flora of Japan. The Japanese list two rhododendrons under the title of R. yakushimanum. The first, R. yakushimanum insulare is an azalea and is found widespread throughout the island of Yaku Shima and closely resembles the species of R. indicum. The other variety and the one to which this paper is devoted, is R. yakushimanum montanum. This rare and highly prized rhododendron species is found only at the summits of Mt. Kuju, Mt. Yaedake and Mt. Hanano-Ego on Yaku Shima.
The first plant reaching the western world was received by Lionel de Rothschild of Exbury, England some 35 years ago when it was sent to him by K. Wada of Numazushi, Japan. This plant was a specimen of particular excellence in that it was a perfectly formed hemisphere, densely compact with dark green foliage. Its leaves were about 3" long and rolled in an extremely convex manner completely obscuring the tomentosum undersurface. Its flowers maintain a perfectly erect truss of pale pure pink. This aristocrat is an ideal dwarf and had attained a height of 2-3 feet and a breadth of some 4 feet at maturity.
It is little wonder that M. H. Sumner titled his paper in the October issue of 1958 American Rhododendron Society Bulletin "An Outstanding Rhododendron." He considered this the most outstanding rhododendron of any he had ever seen, which is in complete agreement with the author. Mr. Francis Hanger, curator, Wisley Garden has compared the plant at the test gardens of the Royal Horticultural Society as a much larger and perhaps better specimen than that of the original plant from which it was derived in Exbury. Comparing the plant at Exbury which I saw some seven years ago with those occurring in the wild at the summit of Mt. Hanano-Ego, it is my impression that cultivation under ideal conditions in the western hemisphere produced a better plant than is seen in its native habitat.
A few years later at the Great Park in Windsor, I was afforded the privilege of seeing with Sir Eric Savill, Commissioner of Crown Lands, the new R. yakushimanum hybrids which had flowered for the first time. I was sadly disappointed in the offspring perhaps because I had expected too much of its wonderful parent. To begin with, the unique form of R. yakushimanum, almost semi-globular, was lacking. Indeed, some of the hybrids were quite leggy. The exquisitely convex, small leaves and extremely dense pattern had been lost. The greatest blow of all was the disappearance of the wooly, velvet-like indumentum which is so much a character of the species. Largely due to the choice of the other parent, almost no dwarfs resembling R. yakushimanum were observed. Lastly, from the view point of the New Englander and his harsh climate, none of the crosses included bone-hardy second parents. Until recently the hybrid flowers left much to be desired. In short, the species to date by far excels in beauty any of its hybrid offspring.
The rarity of the R. yakushimanum has made it a collector's item. It is easy to root from cuttings but is a slow grower. In 1952 a nurseryman in England asked 5 pounds ($14.00) for a tiny rooted cutting. In more recent years a few plants have found their way to fanciers both in the northwest U.S. and a scattered few on the eastern seaboard. My single plant rooted from a cutting given to me by Donald Waterer at Knap Hill was a tiny show piece in 2 years. Despite some 400 species of rhododendrons under cultivation, it became my pet and was given the most select spot in the pit house for continued growth.
One thing is quite certain. The plant is not to be found in any other part of the earth except on Yaku Shima and the chief forester of this island claims that the plant is not available anywhere on the island except at the very peaks of the mountains. R. yakushimanum resembles R. degronianum and perhaps to a lesser degree R. makinoi, a native of mid and northern Japan. R. makinoi does not grow on Yaku Shima.
On August 20, 1959 I started out on a round the world jet flight with short stops to pick up second wind in England, U. S. S. R., Nepal, Thailand, Hong Kong terminating in Japan. The purpose of this jaunt was to explore Yaku Shima (Shima-Japanese for island), home of the Rhododendron Yakushimanum insulare. But for this rhododendron I might have spent my holiday in the mountains of New Hampshire!
Four days after the Boeing 707 landed in London (6 hours), I was off for Paris where I picked up the Russian jet (Tupolev-104). I was the only English speaking sardine squeezed into the speed box. Some 4 hours later we landed in Moscow on an airfield where 25 or 30 jet planes were moored! (The Soviets have been flying jets for 5 years). My 5 days in the Soviet capital was a revelation, but this account must be confined to Yaku Shima. Another jet hurried me south over the Himalayas to Delhi, India. Then came a series of small plane hops first to Agra for the Taj Mahal. Then off to Banaras for the Ganges, its filth, its incomprehensible faith and its dead. A delightful sojourn in Nepal, opened to the world only a few years ago. Calcutta where the buses were stoned and a policeman decapitated during communist hunger riots. The great heat, humidity and poverty with thousands sleeping on the roads and sidewalks, homeless and hungry. Then Bangkok, clean, fascinating, turnip topped gilded temples, a shutter bug's delight. Hong Kong, most fascinating of oriental cities, almost completely Chinese, with refugees pouring from across the China border daily creating one of the world's great housing problems. The finest modern ferries anywhere connect the island of Victoria with the mainland (Kowloon) and shopping at its very best barring no other free port in the world.
Off to Japan, cultured, beautiful, exquisitely polite Japan. A short stay in Tokyo, a stop at the shrines of Nikko, Mt. Fuji and Lake Hakone. Then heading south to Kyoto, Nara and Osaka. From Osaka by plane to Kagoshima, most southerly city of the Japanese mainland. At this point, necktie and long sleeve shirts were put away in my bag for shorts and sport shirt.
Yaku Shima is an almost perfectly circular mountainous island lying in the sub-tropical China sea 150 kilometers south of the Kyushu main land. It is in the typhoon highway and during August and September averages between 20 and 25 typhoons. The approach to the island is only by a tiny tramp steamer which plies between it and Kagoshima whenever weather permits. One must get to the island between typhoons at this time of the year. By the same token it is easy to be marooned for several weeks on the island awaiting a calm sea. The overnight steamer ride is rugged and can prove a chastening experience. The vessel drops anchor about ¾ of a mile from the little village of Anbo while baggage and the few passengers, chiefly Yakushimites are dumped on to a sampan and chugged or rowed ashore.
Chickens, pigs, dogs and humans travel alike on this transport. My arrival occurred during a smooth interval (typhoon 14 had just blown by). The trip to the island was tremendously aided by the Japanese government, department of agriculture. I had written several months in advance for permission to explore the plants of the island and to bring back seeds and cuttings of R. yakushimanum. In characteristically Japanese understatement, they said they would help-no further details. Upon arrival in Tokyo, chief liaison officer H. Matsuo, department of agriculture was waiting for me at the hotel. He had written to Kagoshima to clear the way for me. Special permission is necessary since Yaku is a national park. In Kagoshima, the chief forester greeted me at the ship and sent a government employee along with me on the overnight ride. On Yaku itself, the local superintendent of forests was prepared for my arrival. I was lodged in a tiny Japanese inn operated by the department of forestry. Then came the exciting ascent of Mt. Hanano-Ego.
The island is a rain forest of some note. Japanese say that it rains for 35 days every month at Yaku. The forestry department reports an average of 10,000 mm of rain per year (about 370 inches). Its shrubbery and tree population is jungle-dense on all parts of the island but especially so on the mountain slopes. The mountains rise sharply and are creased by deep ravines through which cold mountain streams race down to the sea. The pride and joy of the island is the giant Yaku cedar which easily rivals our own great California cedars. These are logged on the mountain sides by government foresters under the most perilous surroundings. The huge sectioned logs are hoisted on tiny platform cars and rolled down the mountain side on the most perfectly graded railroad system. The narrow gauge tracks run from the port of Anbo some 27 kilometers winding along the narrow paths of the steep slopes to a level of 1200 meters above sea level. Passage for me and the two guides provided by the Japanese government was provided in the form of a tiny gas-engine car half the size of a jeep. It chugged its way curving and climbing the slopes at about 10 miles per hour. We crossed hundreds of trestles supported by mammoth cedar beams without railings. We crossed ravines 500 feet deep which tightened my clutch on the seat. One does not dare to release a previous hold even to scratch his nose during this climb. The views here were breathtaking. It rained constantly so that I was well soaked by the time we reached the end of the line. On our way up I saw some 30 children in cars awaiting a ride to school 10 kilometers down the mountain. I shudder to think that the kids made this trip twice daily the year round.
At the rail's end a huge number of tremendous cedar logs were being stacked by the loggers. All greeted us with a friendly bowing and smiles. I have never met more friendly or gentle people.
We started our hike up the mountain with no let up in the torrential downpour. The climb to Mt. HananoEgo (1800 meters) did not require ice axe or rope but it did necessitate climbing on all fours some of the way. We crossed deep ravines walking on single cedar logs over gushing mountain streams below. The walking surface of the log had been roughened long ago by axe for better footing. I was amazed that my rubber shoes did not slip on even moss covered logs. Although we made a hundred or more such crossings, I did not meet with a single mishap. Thigh and leg cramps were mild experiences which disappeared in a short while.
The heavy rains changed to mist which is almost always present on the slopes. Fresh cold mountain water collected in my water proof cap provided refreshment both stimulating and thirst quenching. I was soaked through and through despite the foul weather gear so that I could not be sure how much was perspiration and how much was due to rain. Through all this the guides chatted away completely oblivious of my presence. All the way up the vegetation was dense. Numerous tiny alpine flowering shrubs, Pieris japoniica, Camellia, roses, R. keiskei and Lycopodium everywhere. A fern fancier would go out of his mind with the tremendous varieties available in the forest. Sphagnum 6 inches thick lay on water soaked boulders like a soft carpet. Giant cedars, hemlock, red pine, cypress, spruce and magnolia trees dotted the steep hillside. No signs of R. yakushimanum as yet despite the fact that we had reached the level of 1400 meters. At our next stop for a breather, I again questioned the guides-"no yakushimanum"? They pointed to the summit with a laugh. When we reached 1550 meters, the first appearance of R. yakushimanum as an occasional shrublet in beds of Pieris japonica and moss was noted. These were scrawny in the dense shade of the slope. On a sheltered plateau we came to a camping ground with a tiny stone hut built for those stranded during storms. We stopped here and built a fire broiling fish and eating our cold steamed rice carefully packed for us at the inn. Another gulp of delicious cold stream water and we headed for the top. Some 30 or 40 meters higher I noted that most of the trees had been left behind and only low growing cedar brush and occasional Pieris covered the mossy ground. The wind now began to whine. The shrubs of R. yakushimanum were now becoming more plentiful. I couldn't resist stroking the thick glossy leaves. None were as compact as those I had seen under cultivation. Seed pods were found only on those plants in the open. Although only one variety of R. yakushimanum montanum is listed by Japanese botanists, I believe there are actually three varieties and perhaps even more. (Fig. 3) As we approached the summit, the plants became more numerous growing in clumps. At the peak I observed a strange mixture of the elements. Despite the bright sunshine a constant fine rain kept falling and the wind whipped our skin mercilessly. We hastily gathered our cuttings and seeds and packed them into plastic bags. Snapping photographs of the surrounding terrain was difficult because of the strong winds whipping rain into the lens of the camera. With arms loaded I reluctantly left this wondrous garden and started our descent. It had taken us 6 hours to make the ride and climb.
Fig. 3. R. yakushimanum showing the three
distinct types of foliage on the plants growing
on the island of Yaku Shima.
The long ride down the mountain was a new experience. Our motor car was no longer there. Instead we used a small platform, motor-less truck (no railings on the sides). Words are so inept at describing this hair raising ride down the mountain. A hand brake was operated by one guide in a standing position. The other guide and three other foresters were perched on the platform truck. I was placed in the center simply because I was the heaviest object on the platform and gave better ballast. My precious cuttings were jammed between my legs and with both hands holding on for dear life we started the long roll down. We churned down the grade for the 27 kilometers without a stop! I can only compare it to a roller coaster at Coney Island, only this was 15 miles long and no railings. Aside from the heart quakes and aching buttocks, the scenery was fit for the finest travelogue.
Approaching the lower third of the mountain we encountered heavy wind and my first glimpse of the China Sea. As we approached the port, the ocean looked like a kettle of boiling water. Typhoon No. 15 had arrived. That night the walls of the inn quaked. For the next two days not a vessel could be seen. The typhoon went on to strike the mainland at Hanshu and left 5,000 dead in its wake. On the third day the sea became calm and the sky cloudless. Word reached me that a ship would arrive in two hours through the forestry office. I was ready. I had been ready for this moment for the past two days.
My guides refused a tip but graciously accepted a few bottles of port wine which I was obliged to share with them that night.
A careful study of the cuttings which I have obtained from the top of Mt. Hanano-Ego indicates that there are at least three varieties of R. yakushimanum. One variety grows to a height of approximately 4-5 feet and is characterized by a loose habit in growth and leaves that average 3-4 inches in length. The leaves are moderately pointed but lack the convexity of the plant that we have been accustomed to see. I have no knowledge as to the flower of this variety. It resembles R. degronianum more than the next two varieties. I have taken the liberty of naming the three varieties largely in keeping with the characteristics of the leaf. The first variety which is the largest for the sake of convenience R. yakushimanum planum largely because of its flat leaf. It is found at the lowest portion of the summit and is the first variety that is encountered as one climbs the mountain (approximately 1500 meters elevation). In its form and habit it is not a desirable plant.
The second variety is a true dwarf rarely attaining a height of more than 2½ feet in the wild. Invariably it is found on the exposed portions of the summit and is much more dense than the previous variety. The leaves are considerably smaller averaging 1½ to 2½ inches in length and have a tendency to rounded margins with slight convexity. Its indumentum is a darker beige than the previous variety. This form is conveniently called R. yakushimanum parvum because of its smaller stature and smaller leaf. From the gardener's point of view this is a much more desirable plant and since it grows in a rather cold spot which is exposed to full sun, it may prove sufficiently hardy for use in the northern United States.
The two varieties just described were found on the windless side of the mountain summit. In making our ascent to the mountain top we came to the windy side of the peak which was drenched with a filtered sunshine through a fog of mist with the wind bellowing at an estimated speed of 70 miles an hour. It was difficult to maintain a perfectly erect posture in this blow. However, on this wind-swept side the finest of the three varieties was found. This is a plant which reaches a height of about 3 feet growing in a mass of cypress brush interspersed with Pieris japonica. A carpet of 5 inches of lettuce-green sphagnum covers the sandy loam which is interspersed with the rocky sub-soil. A test of the acidity of the soil medium proved it to be a pH of 6.2. The foliage of the last variety is extremely dense only where it is fully exposed to the wind and sun. The individual leaf 3½" long and narrow is curled almost into a complete circle protecting the delicate hairy stomas of the under leaf from the brutal sun and wind to which it is exposed 25 hours of the day throughout most of the year. These plants are under snow for about 5 months of each year. The coldest temperature recorded at the summit of the mountain has been 5 below zero by the forestry department of the island. Comparing this last variety with those that I had seen in England, it was my impression that it was from this choice group that the plant sent to Exbury was selected. It is therefore also the same plant as that at Wisley. However, a plant that I saw at Knap Hill Nursery in Bagshot probably was of the Parvum variety with the small round, slightly convex leaf but with the indumentum resembling that of the other two varieties. Without doubt the convex variety is the gardener's choice. This select group therefore should be titled R. yakushimanum convexum. I was able to collect seeds from all three varieties. These were more plentiful only in the completely exposed areas. The plant is very shy in flowering in the semi-shaded zones and of course, no flowering was observed in the wooded areas where little sunshine permeates the trees.
R. yakushimanum roots readily from cuttings in a period of 8-12 weeks. It has survived to perfection in a pit house where the temperature has reached zero degrees and at the end of two years is a compact globe of foliage measuring 6 inches in height and 5 inches in diameter. It is slow in growth and each year's growth is characterized by a short stem which is gnarled and rarely exceeds three quarters of an inch in length. The seeds germinate quite easily in a matter of three weeks and at the end of one year the seedlings measure between 1 and 1¾ inches in height when grown on pure sphagnum.
The crosses made with R. yakushimanum as noted by Mr. Sumner and others have been disappointing. As far as I can determine, rhododendrons discolor and decorum are the hardiest parents that have been used to date in the crosses. Undoubtedly in the very near future crosses will be made with the much hardier species as well as hybrid varieties and perhaps we shall one day acquire a dwarf or semi-dwarf hybrid of R. yakushimanum whose indumentum will be preserved and some of its fine qualities of foliage and form may be retained.
Aboard the steamer on my way back to the mainland I kept thinking of the wondrous selectivity of nature as the mountains of Yaku Shima faded in the distance. Was it not remarkable that R. yakushimanum could be found only on this island and nowhere else in the world, and at that, only on its highest mountain peaks. What is there about this island that boasts of a Yaku cedar, a Yaku rose and even a distinctive Yaku dog. And to think that I had never heard of Yaku Shima until introduced to a certain rhododendron bearing its name!