JARS v39n4 - Rhododendron nakaharai, A Taiwan Endemic

Rhododendron nakaharai, A Taiwan Endemic
Polly Hill
Wilmington, DE

R. nakaharai , named for the botanist Nakahara, is not very fully covered in rhododendron literature, at least for the amateur who can not read asiatic writing. The R.H.S. Rhododendron Handbook of 1963 lists it briefly on page 122. "Creeping shrub... Flowers up to 1 inch long, dark brick red, Formosa". There is no mention of where in Formosa. H. L. Li's Woody Flora of Taiwan also 1963, lists it first in this fashion, on p. 698. " R. nakaharai Hayata in Jour. Coll. Sci. Univ. Tokyo 25 (19): 153 1908... A low shrub, often prostrate... Corolla scarlet... c.3.6 cm (1½") long and 4 cm (1¾") across." Compared to the description in the R.H.S. Handbook of 1963, this describes a plant superior horticulturally. The diversity within the species is becoming apparent. In the Second Edition of Lee's The Azalea Book , 1965, p. 242, Mount Morrison is given as the source of the species.

At Barnard's Inn Farm on Martha's Vineyard, zone 6, south of coastal Massachusetts, I grew the following plants of the species R. nakaharai .

#61-80-C a compact plant resulting from open pollinated seeds of the species growing in Dr. T. Rokujo's garden in Tokyo. As I know it now it is the Mount Morrison form, the first known type, within the rich complex of the species.

#69-074 cv. 'Mount Seven Star' from Chi Hsien Shan, a mountain of 1120 meters (3,800 feet) in northern Taiwan. Thanks to the persistent efforts of my friend, Ann Fielder of West Tisbury, Massachusetts, I received seeds collected by C.S. Kuo of Tai Da University in Taiwan. He collected the seeds on the mountain by that English name at 800 meters (2,700 feet) on November 16, 1969. To quote the Weedy Flora of Taiwan , p. 609 " R. nakaharai is endemic in northern Taiwan in hills about 1,000 meters, (3,300 feet) in the Tatun range." Chi Hsien Shan is just north of Taipei.

#71-21 a form received as PI 325035 from the U.S.D.A. Collected wild as seed, it appears to be a hybrid with R. oldhamii , another endemic. R. oldhamii is a shrub 3-4 meters high. My #71-21 is flat on the ground, less hardy than my other living hybrids of R. nakaharai , but sharing its prostrate habit and rich scarlet flower color, with branches reaching wide on the ground. Dr. Creech, who collected widely in the East, assures me such a hybrid is to be expected as these two species, with several others, are scattered indiscriminately through the mountains.

#73-132 R. nakaharai cv. 'Mariko' I received a small rooted cutting from Dr. August Kehr in December 1973, which he had received from Mr. Peter Cox of Scotland, who received it from Dr. Rokujo, I am told. It has been in my fenced in area known as the Play-Pen since 1976. This rock garden treasure, named for Dr. Rokujo's daughter, is a very tightly grown little mound, not slow to bloom, but slow to develop and spread. Its form and flower very closely match my 61-80-C.

#74-050 This plant came from the Species Foundation #73/195. Its form is impeccable, smooth surface, tight low mound. But the flower color is flawed, appearing a trifle washed out. It is growing in my Play-Pen side by side with my original plant of 'Mount Seven Star.'

I am growing #67-62 a form labeled R. nakaharai from the U.S. National Arboretum which they received from Dr. Dietrich Hobbie of West Germany. It appears to be a hybrid in that it grows fast, wide, and tall. It lacks the ear marks of the "true" species which is slow, compact, tight and twiggy. The flowers are brick red. In the 17 years I have observed it its form and flower color do not, in my opinion, merit selection.

Many R. nakaharai hybrids, thanks to the breeding of Dr. Rokujo of Tokyo, also grow in Barnard's Inn Farm. The best selections of these constitute the North Tisbury Azaleas, which group name covers other cultivars and species as well. But that is a different story.

The first plant of R. nakaharai to reach English gardens, I believe, was cv. 'Mariko,' from Dr. Rokujo. That is the small, tight, mounted form represented in my collection by #61-80-C, #74-050, and 'Mariko' itself. My cv. 'Mount Seven Star' is somewhat different, horticulturally speaking, from the three fore mentioned plants. After a period of adjustment it grows a bit broader, the leaves are a little darker and hairier, and the flowers sometimes open a week later, conspicuously larger and richer in color. They are equally hardy in my experience, and each has a distinguished habit of growth, tight and densely twiggy. Cv. 'Mount Seven Star' is easy to pick out in a mixed planting of azaleas from its leaf and habit alone.

Mr. Barry Yinger, Curator of Asian Plants at the U.S. National Arboretum, after collecting through Taiwan, assures me that R. nakaharai has many forms all through the mountains of Taiwan. And why not? Is this not frequent among wild populations, generally? Even on the 100 isolated square miles of Martha's Vineyard Island the native shrub, Ilex verticillata , has enough diversity to lead a well known holly expert to question the identity of 1 or 2 species on minor points. As a good American (with diverse genes of my own) I am a lumper and not a splitter. Another example of wild hybridity or diversity is R. atlanticum cv. Marydel, selected to represent the Choptank River hybrids. R. nudiflorum is considered the other species involved in the wild cross with atlanticum . Seeds of the Choptank River strain breed true. There is a slight variation in flower color but they blend together almost indistinguishably. If they differ from what is considered the "true species" the differences are such that the subject enters the field of taxonomy rather than horticulture. To the gardener they are still R. atlanticum . Just so with R. nakaharai in Taiwan, in my own small sampling. Yushan, over 1,300 meters, (4,400 feet), is the Chinese name for Mount Morrison, where the species as it is known in Japan, for example 'Mariko', had its origin. At least 80 miles north is Chi Shien Shan, 1120 meters, (3,800 feet), Mount Seven Star in English, where grew the parent of my #69-074. In these 80 miles how many variants may yet be found? In the case of R. atlanticum 80 miles or so south of Choptank River other variants of the species become more common. Why not also in Taiwan? Additionally, the mountainous terrain of Taiwan, as opposed to the sandy plains of lower Delaware offer a greater variety of habitats and species.

One observation is of interest R. nakaharai cv. 'Mount Seven Star' does not (readily) cross with R. nakaharai cv. 'Mariko.' Although hand pollinated the seeds do not germinate, Dr. Rokujo writes me. He writes me that this year and also two years ago the same cross produced seeds that did not germinate. He also crossed 'Mount Seven Star' with the ARS University of Vancouver plants and they did not germinate. 'Mariko' x Orange form from Greer Gardens had good germination in F1, but not in the F2 generation. The Orange form x 'Mount Seven Star' had no germination. If there is genetic difference enough so that individuals can not be crossed within the group, then maybe we are dealing with separate species. However, it is too soon and there is too little information accumulated to leap ahead so far.

It would be of great interest to know what forms of R. nakaharai crossed with what other forms have produced germination. So far, in my garden, I believe only in one year did any seeds ripen on 'Mount Seven Star.' There were only aborted capsules the fall of 1984. A very few open pollinated seeds were collected from 61-80-C, 'Mariko,' and #74-050 in 1984, for the A.R.S. Seed Exchange.

About the color of the flower in /R. nakaharai : there are detractors I have heard in lecture and in writing, concerning the flower color of the Mount Morrison form of the species, the one first introduced. In my collections there are two forms I judge to have superior flower size and color: #71-21, and cv. 'Mount Seven Star.' Jeanne Holgate, the gifted flower artist, helped me to fill out the registration form for 'Mount Seven Star.' She matched the color of my flower with paint. It was pure cadmium red. Also the visitors who see 'Mount Seven Star' in bloom declare it beautiful and desirable.

That leaves #71-21, the species with a touch of R. oldhamii (?) It has only flowered for me one or two years in the 13 years it has been growing. The color was a handsome strong scarlet and the size large. The plant is very woolly-furry, softly hairy, and prostrate, but less twiggy than the other R. nakaharai plants. It is not very hardy and grows in rather deep shade and shelter. It needs to be tested further south or on the West Coast to develop clearly its true nature before registration or further talk.

Now if one could only cross 'Mariko' with 'Mount Seven Star' what a splendid plant that might be; but if Dr. Rokujo has not succeeded, and if nobody else has, what will the taxonomists say?