QBARS - v21n1 Ornamental Plant Exploration - Japan, 1961

Ornamental Plant Explorations-Japan, 1961
By John L. Creech, Washington, D.C.
Agricultural Administrator, Crops Research Division, Agricultural Research Service
U.S. Department of Agriculture
Presented at the A.R.S. Annual Meeting in Tacoma, Wash.

A plant exploration in Japan was undertaken by the U.S. Department of Agriculture from April 14 to July 28, 1961. Objectives were to investigate the geographical distribution of selected woody and herbaceous plants of Japan and to collect propagating material from important variations of species valuable as ornamentals in American horticulture. This was the sixth in a series of ornamental plant explorations conducted cooperatively by the Agricultural Research Service, U.S. Department of Agriculture, and Longwood Gardens, Longwood Foundation, Inc., Kennett Square, Pa. For the writer, it was the third plant collecting expedition to Japan.

The expedition began in April, at the beginning of the azalea flowering season in southern Kyushu. Japan is the center of distribution of azaleas in the Orient and Kyushu is the most favored locality for azaleas in Japan. Combination of a highly acid porous volcanic soil and a mild maritime climate with moderate, evenly distributed rainfall provides an ideal environment for the development of extensive colonies of azaleas. The timing of the expedition also allowed me to see the famous "Hirado" azaleas in flower. "Hirado" azaleas are grown exclusively on Hirado, an Island in the Sea of Japan, and some Japanese believe that these have the largest and most beautiful flowers of any of the azaleas. Approval had been obtained from the Japanese Ministry of Agriculture and Forestry to visit Hirado to confirm the existence of such an azalea race and to obtain a representative collection of cuttings and plants for testing in the United States.

Kyushu and the Kurume Azaleas

Southern Kyushu is the center of origin of our evergreen azaleas. On the cool, humid outer slopes of several volcanic cones from 800 meters continuing up to 1,700 meters, a variable array of azaleas thrive. In some places hybrid swarms form waist-high thickets through which one must force his way. At the lip of the cones, an entire plant of Rhododendron kiusianum can be cupped in two hands. These azaleas can be sorted into related types according to the elevations at which they occur and to the localities to which they are restricted.

Three mountains provide the most plausible clues as to the origin of the Kurume azaleas, foremost of the cultivars that have evolved from the species found in Kyushu. These mountains are Sakurajima, unique, active volcano overlooking the city of Kagoshima; Takakuma, a mountain chain adjacent to Sakurajima and Kirishima, a group of high volcanic cones famous for hot springs. These mountains are all within a 30-mile radius of Kagoshima. The species that are of significance to the origin of Kurume azaleas and that are found in these mountains are: R. kaempferi ( R. obtusum var. kaempferi ), R. kiusianum ( R. obtusum var. japonicum ), and R. sataense , a comparatively new azalea not mentioned in any earlier English literature.

Sakurajima

Sakurajima (1,118 meters), an isolated, symmetrical volcanic cone, juts out into Kagoshima Bay, overshadowing Kagoshima City. The slopes of this active volcano are so covered with fresh lava rocks from constant eruptions that the upper portions do not support a forest cover. Yet, among huge lava boulders, azaleas thrive in profusion and present a variable array of colors from light pink to strong, reddish purple. I spent the entire day of April 24 wandering the paths that wind around the slopes of Sakurajima trying to draw some conclusions. Rhododendron kaempferi is the most prevalent species, readily distinguished by its loose, upright habit, flat to concave, elliptic leaves, and orange-red flowers, up to 2 inches across. A swarm of types closely resembling the Kurume azaleas in flower color and plant habit also grows here. Among brittle lava blocks also grows an azalea that has lavender flowers similar in size to those of R. kaempferi . Some Japanese refer to this azalea as " R. obtusum ." Plants (PI 231952) under this name collected on Sakurajima were obtained from the Kyushu Horticultural Station, Kurume, Kyushu, in 1956. Studies by Japanese horticulturists suggest that the majority of azaleas scattered over Sakurajima are hybrids between this azalea and R. kaempferi . In all my visits to Sakurajima, no azalea similar to R. kiusianum , which inhabits the upper limits of Mt. Kirishima, could be found and the taxonomic status of the azaleas of Sakurajima is still a question.

I left Sakurajima with a party of Japanese botanists in the late evening of April 24 and on the following morning we departed by jeep for Takakuma, the ash-covered mountain chain paralleling the coast of Osumi Peninsula. The route led through gorges inhabited by broadleaf evergreens and in one of these called Sarugajo (Monkey's Castle), we spent the better part of the day collecting plants. This is one of the few places in Kyushu where Rhododendron serpyllifolium grows wild. This tiny-flowered azalea grows on the moss-covered boulders along the ravine walls and varies in flower color from white to pink. One plant with dark-pink flowers (PI 274545) was collected.

Takakuma

The Takakuma mountains (1,236 meters) consist of a series of gradually ascending rises to the highest point on the Osumi Peninsula called Onogara. It is said that the low temperature at the Forestry Station (700 meters) is a -7° C. in January and that snow falls about 10 times between December and March attaining up to 75 centimeters. The azaleas are the conspicuous feature of the open meadows of Takakuma. From sea level to about 500 meters, Rhododendron kaempferi abounds on rock outcroppings and on ledges along trails. The flowers are typically brick red and the leaves large and scattered along the branches. At about 500 meters, a new azalea appeared. This is R. sataense Nakai. These plants are dense and mound-like, with flowers that range from pink to purple with broadly overlapping petals and shiny leaves that are flat to convex. This newly named species more nearly approximates the cultivated Kurume group than does either R. kaempferi or R. kiusianum . Both living plants and seed of R. sataense were brought into cultivation as a result of this exploration.

Kirishima

The Kirishima mountains (1,700 meters) are the highest volcanic cones in southern Kyushu. On the evergreenclad lower slopes and in the grassy meadows at higher elevations occurs a complex of azaleas that have figured largely in the literature on the development of the famous Kurume azaleas. In 1955, I had climbed to the rim of the volcanic cone Karakuni-dake (1,700 meters) to observe the colonies of Rhododendron kiusianum , a small-leaved, purple-flowered azalea. When this azalea hybridizes with R. kaempferi from lower elevations, a bewildering array of seedlings with pink, scarlet, crimson, and purple flowers results. I repeated the observation, April 28-29, (luring the peak of the flowering of azaleas solely to assure myself of the fact that one could clearly distinguish between localities where R. kaempferi and R. kiusianum occur. In all of my travels in Kyushu, I never found R. kaempferi above 800 meters elevation, although in northern Honshu, it grows at 1,200 meters near the top of Goyo-dake. R. kiusianum can be found only in the bare alpine meadows between 1,200 and 1,700 meters, except where plants have been brought down and planted around the hot spring inns for which Kirishima-jinza is so famous. As one approaches the rim of the volcano, the steep slopes, now completely fogged in with chilling rain, now brilliantly clear, are dotted with tiny plants of Ilex crenata and R. kiusianum . When brought into cultivation, this azalea maintains its dense small leaved habit and tiny flowers. Both purple and white forms occur in the wild, but the latter is rarely seen.

In the forest below the several inns is a magnificent waterfall called Senrigataki (meaning 1,000-mile waterfall). Along the winding stream-bed, Rhododendron nudipes (closely related to R. reticulatum ) with flowers varying from red to purple was in full bloom. Although Rhododendron kiusianum must figure in the background of the Kurume azalea, I cannot concede that this azalea is the phylogenetic type of this race. I prefer to recognize it as the specific entity accepted by the Japanese rather than use the more common classification, R. obtusum f. japonicum Wilson. R. kiusianum has crossed with R. kaempferi to produce a remarkable hybrid swarm bridging the gap between these azaleas, but I have seen in my travels no locality where R. kaempferi and R. kiusianum are so intermingled that I would wish to relegate these species to subspecific status on the basis of continuous distribution.

Hirado Island

Hiirado is a little-known island adjacent to Kyushu reached by about a 2-hour train ride from Sasebo and a short ferry trip from Hirado-guchi to the island of Hirado. This island, which is now relegated to the occupation of fishing and subsistence farming, is steeped in Japanese history and romance.

Being isolated and scenic, Hirado became a favorite spot for the feudal samurai of older Japan and their palaces dotted the gentle slopes. It might also be said that many of these noblemen delved in the smuggling trade with the Chinese pirates and thus enhanced their fortunes. But the gentlemen did have elaborate gardens and these were planted largely to azaleas. Evidently, the popular Rhododendron scabrum was grown here as it was in the city of Kagoshima. This azalea was brought to Japan from the Ryukyu Islands.

The azaleas of Hirado are a distinct group characterized by unusually large flowers, some measuring up to 13 centimeters across and this character can easily be traced to R. scabrum . The color range is from pink through red to purple, which suggests the infusion of R. mucronatum and R. phoeniceum . My Japanese friends believe that R. simsii , from China, is also involved in the development of the Hirado azaleas, but I saw no plants of this species in any Hirado gardens nor the suggestion of it in the various hybrids on Hirado. It is not grown anywhere in Japanese gardens.

The Hirado azaleas are located in individual private gardens so one has to visit many places to see them all. Some of these gardens date back more than 300 years during which time selections were continually made from the spontaneous populations that sprang up among the original azalea plantings. Today, approximately 230 varieties of Hirado azaleas are recognized. Of these, my colleague, T. Tamura, Kurume Agricultural Station, Kyushu, suggested a list of 30 varieties that are representative of the range of variation in the Hirado race. These were collected either as small plants or un-rooted cuttings from the various gardens and sent to the U.S. Department of Agriculture for propagation and evaluation.

The merits of the Hirado azaleas, insofar as American horticulture is concerned, have yet to be determined. Originating from R. scabrum , they are certain to be limited in hardiness to the southern azalea-growing regions.

As for flower character, size is not necessarily a criterion for quality, but the colors are rather brilliant and the plants are prolific and vigorous. Their massive habit and height (some bushes are 6 to 8 feet tall) and large leaves suggest that they would serve best as background plants in parks and other locations where space is ample. Although the Hirado azaleas were the primary objective of visiting the island, a number of plants seen and collected are worthy of note. In a small fisherman's garden at Ushirobira, I found a white-flowered form of R. weyrichii that originated on Goto Island. Regrettably, none of the cuttings made from rather weak shoots survived, but herbarium specimens at least record its existence.

Seidagawa and Kosho-Dake

The last days in Kyushu (May 13-14) were spent in the mountains of central Kyushu. A small peak at Seidagawa (520 meters) is isolated in the hot central plain and proved to be an unusually exciting locality. Here Rhododendron japonicum grows in profusion. Earlier Western World records do not describe this azalea as growing wild in Kyushu. Above the town of Kusu in a pine-chestnut region, R. japonicum grows in hot sunny meadows, quite different from the cool bog habitats ordinarily frequented by this azalea. Furthermore, here can be found the broadest range of color variation occurring in the species. The colony includes the yellow form, aureum . Despite earlier observations by Wilson to the effect that the yellow form is rather rare, it accounts for about a third of the colony I visited at Seidagawa. Furthermore, seed collected from the yellow-flowered plants will produce a population of predominantly yellow plants, readily distinguished as seedlings by their pale-yellow winter buds and leaves which turn yellow rather than red in the autumn. This form is probably the yellow azalea described by Kaempfer as "Rjuku tsutsusi flore igneo, punctis petalorum croceis, apicibus rufis." Wilson questions this point on the basis that Kaempfer could not have seen it enroute from Nagasaki to Kyoto. On the contrary, this journey would have allowed Kaempfer to see R. japonicum . Whether these southernmost colonies of R. japonicum will be significant in terms of heat tolerance must await the observations of others, but the recording of this highly significant colony and the availability of yellow flowered populations should be important to the breeder of deciduous azaleas.

Ashitaka, Jurigi Village, and Hakone

The return from Kyushu to Tokyo was by way of Mt. Ashitaka near Hamamatsu, Honshu. The purpose of my visit (May 16-17) was to examine a naturally occurring hybrid between Rhododendron kaempferi and R. macrosepalum named R. X tectum Koidz. The roadsides and ditches were frequented with both R. kaempferi and R. X tectum , similar in color but easily separated by the glandular hairiness on the prominent calyx lobes of the hybrid. Magenta-flowered R. macrosepalum , on the other hand, frequented the shade of the high pine woods. Wilson also noted that these two, R. kaempferi and R. macrosepalum , grew together by the thousands and were easily recognized from train and car windows.

Ashitaka is the locality for an azalea new to us, Rhododendron komiyamae Makino. This species is referred to by the Japanese as "Ashitaka tsutsuji" in reference to the fact that it grows at the summit of Mt. Ashitaka (1,098 meters). It is a small tree or large shrub 10 feet tall, semi-evergreen with rather narrow leaves, acute at both ends. The flowers are purple, 1 inch across, and have 10 stamens. In its social relationships with R. kaempferi , R. komiyamae compares favorably with that described for R. sataense and R. kiusianum in Kyushu. Behind a small farmhouse near Jurigi Village (900 meters), I came upon a colony of azaleas in bloom. They largely resembled some of the Kaempferi hybrids I have seen in cultivation. The flowers varied from the brick red of R. kaempferi to the purple of R. komiyamae . The plants grew on top of moss-covered rocks protruding out of the boggy ground. These were upright plants 6 to 8 feet tall and characterized by 6 to 10 stamens. Earlier in my ascent, I had seen R. kaempferi in flower at lower elevations and had also climbed to the summit of Mt. Ashitaka to locate R. komiyamae in a rain that turned into light snow. It was on my return that I chanced upon this hybrid swarm, which gave all evidence of intergradation between R. kaempferi and R. komiyamae . This is not a new azalea, but must be what Wilson described as R. obtusum var. kaempferi f. mikawanum , which he collected in the Ashitaka mountains. We have on hand collections of the hybrid swarms, as well as R. kaempferi and R. komiyamae , from Ashitaka.

From Ashitaka, the route to Tokyo led to one more collecting place Komaga-take in the Hakone Mountains, a small peak (1,354 meters) reached, pleasantly, by cable car. Here, one can find the prostrate R. tanakae . Strictly an alpine plant, this curious and rare species has thick, almost sessile leaves and minute white flowers that appear in July. Brought down from the mountains it promptly dies and is rarely cultivated by the Japanese. R. wadanum also grows in this region. Like its close relative R. reticulatum from which it differs in rather minor characters, such as having a partly glandular style and slightly different form of capsule, R. wadanum grows as single plants rather than in colonies. But these are a brilliant rose purple in flower so that one is drawn to them.

Abukuma Range

Rhododendron kaempferi had already flowered in the hills but along the edges of rice paddies near the ocean, it was still in bloom on May 28. At the sea cliffs, R. japonicum grows in semi shade mixed with Kaempfer's azalea, and it was also in flower. Unlike the colonies of azaleas in southern Japan with their broad range of color, the flowers of R. japonicum here are limited to the typical orange-red shades. A single plant of R. kaempferi had hose-in-hose flowers, the first of its kind I had seen in the wild.

Ootakino is the highest mountain of the Abukuma Range (1,193 meters). We traveled part way by jeep along a logging road and on foot to the severely cutover meadows at the top. The open fields are inhabited by Rhododendron japonicum and the plants are multi stemmed from the constant cutting back by harvesters of small brush. In the few wooded areas bordering these brush fields, R. kaempferi grows up to 6 feet tall, straggly, but brightly coloring the woods with its salmon colored flowers. Occasional plants of the white-flowered R. quinquefolium were flowering. Seldom does one see these three azaleas at their peak of bloom in one locality.

Lake Towada and Mt. Hakkoda

Lake Towada and Mt. Hakkoda (1,600 meters) are on the midline of northern Honshu. Although the lake area is highly scenic, the forests are mainly deciduous and it is on Mt. Hakkoda that the plant collector will find excitement.

Rhododendron japonicum is the most spectacular azalea on this mountain. This is the northern limit of natural distribution and a remarkable contrast to the colonies found blooming in Kyushu in early May. It was in full bloom on June 21. The plants were scattered throughout the bogs, often at the very edges of the pools. It is a meadow plant here as elsewhere in Japan. At its northern limit, R. japonicum is a vigorous plant with large glaucous leaves. The flowers are uniform in color throughout the stands. It is a glowing orange red and the trusses of 10 to 12 flowers are compactly borne. By far, this is the finest form of the species I have ever observed in Japan. If it proves to be a distinct biotype for color and form, this type will be a most useful azalea for areas requiring hardiness. The winters at Hakkoda are extremely cold but the snow accumulates to several feet and remains until late in the spring. This azalea was not found again as I traveled in Japan north of Mt. Hakkoda. One advantage from securing material of this type is the opportunity to conduct research on inheritance patterns for azaleas as a basis for further improvement.