Rhododendron weyrichii forma albiflora Sugimoto
Dr. John L. Creech, Director
U.S. National Arboretum, Washington, D.C.
I first became acquainted with Rhododendron weyrichii Maxim., in 1952 when it flowered at the U.S. Plant Introduction Station, Glenn Dale, Maryland. It is not a commonly cultivated azalea and other than its initial introduction by E. H. Wilson in 1914 (4), most of the collections brought into cultivation are from my own explorations of Japan (1).
Rhododendron weyrichii was discovered on the Goto Islands, Japan in 1853 by Dr. Heinrich Weyrich, a physician on the Russian warship, Vostock. The Russian fleet had been cruising near the Goto Islands, probably on an exploratory mission to the newly opened Empire (3).
Rhododendron weyrichii is common throughout the several Goto Islands from the seacoast to the tops of the small mountains. It occurs on the Korean island of Quelpart and on the Japanese island of Shikoku, where I first collected seeds and plants in 1955. Before that, seeds were sent to the USDA from Dairen, Manchuria in 1933, the Tokyo Botanic Garden in 1936, and Hillier and Son, England, in 1940. So there have not been many collections from which to observe this species.
The disjunctive distribution of R. weyrichii has led to several taxonomic determinations. The type of R. weyrichii from Shikoku was considered by Makino (2) as R. shikokianum. Rhododendron weyrichii var amagianum (Makino) Hatsushima was previously classified as R. amagianum, having been identified from Mt. Amagi, Honshu. Rhododendron weyrichii var sanctum (Nakai) Hatsushima was formerly classified as R. sanctum by Nakai (2). The white-flowered form, R. weyrichii f. albiflorum, was described from Shikoku by Sugimoto in 1965 (2).
Perhaps most interesting is my own encounter with R. weyrichii f. albiflorum Sugimoto. During my first visit to Harado Island, Kyushu, in 1961, I found the white-flowered form of R. weyrichii in full bloom in the garden of a farrer, Hiyashi. The plant was thought to have come from the Goto Islands and may be one of the few plants of this type in cultivation in Japan. We collected herbarium specimens and cuttings but the latter failed to root and I abandoned any further immediate attempts to obtain material.
During an exploration in the fall of 1976, I returned to Hirado accompanied by Mr. S. G. March of the U.S. National Arboretum and again sought out the Hiyashi family although it required the help of the City Office records of Hirado to find Mrs. Hiyashi. The dear lady, now a hospital administrator, remembered my earlier visit and was delighted to lead us to the plant again. This time, we were able to gather the few seedpods remaining on the plant and sent them to the National Arboretum.
A small population of seedlings was produced in the hope that we would recover the white form. In March 1979, six seedlings flowered for the first time. To my delight, three of these have white flowers. After 18 years since the original effort, the white form of R. weyrichii has now been established in our living collections. Propagating material will eventually be distributed by the National Arboretum.
In 1978, I visited the Goto Islands with Dr. F. G. Meyer and Mr. S. G. March where we encountered R. weyrichii as a common plant in the low mountains. It also grows down to the edge of the ocean and we found plants clinging to the very edge of a rocky cliff which we had approached by boat. In another instance, R. weyrichii was located in the dense woods above an ancient shrine. Here, R. weyrichii attained the remarkable height of 25 feet. The bark on the trunk was exfoliating. On a small nearby peak, it was a small shrub growing to a height of six feet, occurring mixed with Pieris japonica, Rhododendron kaempferi. and Camellia sasanqua. At Uchiyama Dam, R. weyrichii was abundant and several specimens growing along the road cut were sporadically in bloom.
As a result of our collections, we now have ample material of this interesting azalea from the site where it was originally collected and named more than 125 years ago.
Creech, J., Ornamental Plant Explorations - Japan, 1961; 1966, Vol. 21 No1, ARS 34-75
Hatsushima, S., 1969, A Revision of the Rhododendron sect. Sciadorhodion from Japan. Sci. Rept. Yokosuka City Mus. No. 15.
Trewartha, G. T., 1945, Japan, A Physical, Cultural, and Regional Geography, Univ. of Wisc. Press, 607 pp.
Wilson, E. H. and Alfred Rehder, 1921, A Monograph of Azalea, The Univ. Press. Cambridge, 219 pp.