JARS v44n4 - Rhododendron metternichii variety micranthum - Introduction

Rhododendron metternichii variety micranthum
Frank Doleshy
Edmonds, Washington

In the accompanying account, Mr. Hirokazu Maehara discusses the micranthum form (or variety) of R. metternichii ; also he briefly mentions the Mt. Ishizuchi form. Of the local rhododendron populations that Mrs. Doleshy and I have seen in Japan, these are probably the two most interesting. I have to mention, though, that the full scientific name of "R. metternichii" is now Rhododendron degronianum subsp. heptamerum var. heptamerum - as published by Hara in 1986 and by Chamberlain and me in 1987. Both those papers appeared in the Journal of Japanese Botany , and I also explained the name changes in the ARS Journal for Fall, 1988. I'm sure Mr. Maehara knows all this, yet likes to use "metternichii" as a popular name (not a bad idea).
The micranthum form is found on the Kii Peninsula, a portion of Honshu (main island) which encloses the east end of the Inland Sea. We went there in 1971 because the late K. Wada had told us it was the place for unusual forms of R. metternichii , as we then called it. Our first stop was the mountain town of Yoshino, where the staff people at our inn went out after dinner and brought back rhododendron leaves with the most remarkable copper-colored indumentum we'd ever seen. The next morning they guided us to the source, a small farm in Yoshino producing tea and plants of this one rhododendron.
We picked seed, distributed via the ARS seed exchange as our No. 531, but could not learn from anyone where this form grew in the wild. We hunted unsuccessfully at Mt. Odaigahara (mentioned by Mr. Maehara), and at a high pass east of Yoshino. Then from the highway along the east side of Kii, we hiked up to the Zenki area and, finally, found rhododendrons which could well have been the source of the Yoshino plant. (Seed, No. 541.) This location was about 6 miles south of Mt. Misen, mentioned by Mr. Maehara as an excellent source, and it was along the same central mountain range. Then we drove across Kii to the western coast, via a road a little to the south, from Shingu to Kamitonda. This led through big stands of rhododendrons akin to those at Yoshino and the Zenki area but more varied and, in several cases, with somewhat more colorful indumentum. (Seed, No. 544.) The plants from all three seed collections are interesting, usually with a red midrib on current year's leaves. And now, whether or not you have any of those plants, we suggest that you try Mr. Maehara's seeds.
The briefly-mentioned Mt. Ihizuchi rhododendron, found only at high elevations, has fairly small leaves with rolled down edges and thick indumentum (traits which persist in cultivation). We were led to these plants in 1969 by Forest Superintendent Michikura, and he later sent us seed which we distributed through the seed exchange under his name.
These Ishizuchi plants made us think of the far-north subsp. degronianum and far-south subsp. yakushimanum , which are perhaps the ancient rhododendrons of Japan. And, because of mountain-top isolation on Ishizuchi, these plants possibly received a reduced dose of new traits such as thinner indumentum, which we think came from the mainland Asiatic coast on a piece of land which arrived about 64 million years ago. In any event, I also urge you to grow this one if you can get it.