JARS v44n4 - Rhododendron metternichii variety micranthum: Observations

Rhododendron metternichii variety micranthum
Hirokazu Maehara
Osaka, Japan

Rhododendron metternichii f. micranthum [syn. Rhododendron japonicum var. japonicum ] is simply mentioned as "Omine Shakunage" (Shakunage = Rhododendron) in old Japanese books. But, recently it has attracted more attention, even though it is not a popular type of Japanese rhododendron.
A recent illustrated plant book states: Rhododendron metternichii var. micranthum Nakai; the foliage looks like var. honodoense , some flowers are small. This is called "Yamato Shakunage." However, modern scholars wonder if this form was named by seeing only one specimen? It is a vague situation. According to my observations, this form can be seen on Mt. Odaigahara and on the lower part of the Mt. Omine range.

Mt. Odaigahara, R. metternichii var. 
Mt. Odaigahara, R. metternichii var. micranthum .
Photo by Hirokazu Maehara

Rhododendron metternichii f. micranthum Takeda is introduced as a form of R. metternichii , it is also described simply by mentioning that the flowers are small. I couldn't find any articles with more details.
I observed rhododendrons with thick leaf indumentum and small flowers on the north summit area of the Mt. Omine range, but the diameter of most flowers was 5 to 6 cm. Recently this form has been called "Yamato Shakunage." These plants have deeper pink flowers than the others I observed. The flower color rarely fades. Another characteristic is flower parts that are a little longer than those of other forms.
Both the variety (var.) and the form (f.) have new leaves with a red midrib on the back side of the leaves which persists. This makes them easy to distinguish from other selections.
In the mountains, most leaves are the same shape, but in cultivation, leaves show more diversity in shape and size. There are differences in indumentum color, beige, brown and an exceptionally beautiful orange color can be seen only in the mountains. In cultivation, the indumentum is usually a brick color.
Very good miniature rhododendrons sometimes appear in cultivation. Rhododendron metternichii f. micranthum can develop into a fine dwarf plant.
Rhododendron metternichii var. honodoense grows wild on the lower slopes of the mountains. When collecting seed, you must be careful to gather it only in the "pure" zone. There are many intermediate forms in the mountains.

R. metternichii var. micranthum 
Mt. Omine Range, Mt. Misen,
R. metternichii
var. micranthum Odaiform.
Photo by Hirokazu Maehara

I have sent seed collected on Mt. Inamuragatake and Mt. Misen (Mt. Omine range) to the ARS seed exchange. I collect it to serve as a reference to the species found there. Mt. Misen is an excellent source, but I'm too old now to climb it many more times. In the fall, the daylight is so short that I can collect seed only once. I'd like to select many more types, such as R. yakushimanum .

R. metternichii var. micranthum
Mt. Omine Range, Mt. Misen, R. metternichii var. micranthum .
The beautiful, thick indumentum varies from brown to orange on
these plants from the highest spot on the Mt. Omine Range, the
blossoms from this area are among the largest.
Photo by Hirokazu Maehara

Although the location is different, I must also mention R. metternichii Ishizuchi form. This form grows wild on the highest place in southern Japan. I photographed this form at 1950 meters d thick indumentum. More of this form needs to be collected. In Japanese we have known it for a long time as "Ishizuchi Shakunage." It grows on Mt. Ishizuchi in Ehime prefecture.

R. metternichii var. albiflorum
Mt. Dainichi seedling, R. metternichii var. albiflorum .
Photo by Hirokazu Maehara

In conclusion, let me say that in Osaka, where I live, there is urban sprawl. Many new residences don't have gardens. The land is covered with concrete, creating a desert-like appearance. Growing rhododendrons in such conditions is difficult. In the future, I see the need to grow dwarf plants that will survive heat and drought.

Mr. Maehara is an ARS member from Japan who has corresponded over the years with many members in the United States, including Dr. Franklin West, who forwarded this article to the ARS Journal for publication.