QBARS - v18n2 An Addition to the Yak About yakusimanum

An Addition to the Yak About Yakushimanum
David G. Leach

R. yakusimanum
Fig. 12.  Flowers of R. yakushimanum on a plant
in the garden of Carl Phetteplace, M.D., Eugene,
Ore.  The seed from which this plant was grown
came from Wisley.
Carl Phetteplace Photo

I knew that there was a wide and intensive interest in Rhododendron yakushimanum but the response to my article in the January Bulletin indicates that the preoccupation is best described as feverish. I am therefore adding several additional paragraphs which now exhaust my fund of unpublished information on this beautiful Rhododendron.
The Japanese government no longer permits the collection of R. yakushimanum . At the present time not a plant can be found in the accessible parts of Yaku Island. The land has been stripped bare of this species wherever collecting is easy.
At an elevation of 3,300 feet to 4.000 feet on Yaku Shima a rhododendron closely resembling R. metternichii is found. It has a scanty indumentum and large leaves in addition to other characteristics identical with that species. Mr. Motonosuke Azawa, Vice President of the Tokyo Wild Plant Society, reports this metternichii -like rhododendron as occurring from 800 feet up to 3,100 feet on Mt. Kuromidake.
In the wild R. yakushimanum reaches proportions completely beyond the popular conception of its stature. At 4,000 to 5,000 feet, where it grows among trees, this species reaches a height of 25 feet and has a trunk three feet in circumference measured four feet above ground level, according to Mr. K. Wada, who originally brought this rhododendron into cultivation.
The two little plants of R. yakushimanum, about eight inches in height, which Mr. Lionel de Rothschild in England originally obtained from Mr. Wada in 1936 probably came from a part of the island which has not since been visited by collectors inasmuch as a different road ascending the steep mountain was constructed after the war. The rough terrain makes cross country travel on Yaku Island extremely arduous. Mr. Wada deduces that the plants sent to Mr. Rothschild may have been natural hybrids between the low and the high altitude forms of R. yakushimanum . This seems a plausible assumption to me because of the variation among plants grown from seeds taken from the imported specimen which subsequently became the F.C.C. form.
Japanese hobbyists prize most highly the wide-leafed, dwarf, heavily indumented form of R. yakushimanum which grows in granite rubble from about 5,600 feet to the summit of Mt. Kuromidake at about 6,100 feet. However, it is not a popular plant with the public in Japan, because it blooms too late, after the arrival of hot weather at sea level. By that time Japanese gardeners have become sated with the multitude of colorful spring flowers which are grown in the mild climate of Honshu.