Rhododendron komiyamae and Its Alliance With
Rhododendron kaempferi
John L. Creech, Director, U.S. National Arboretum
Agricultural Research Service, U.S. Department of Agriculture
Washington, D.C.
Summary
A comparatively local azalea species,
Rhododendron komiyamae
, is described with particular reference to its habitat in Japan. Its relationship to
R. kaempferi
relative to naturally occurring hybrid populations between these two species is discussed.
Rhododendron komiyamae
is an obscure azalea restricted to Mt. Ashitaka (1,505 m.), a volcanic cone in the Fiji-Hakone mountain range of central Honshu, Japan. This azalea species was described by Makino in 1926
(1)
Japanese botanists were probably acquainted with this azalea much earlier and Makino had classified an azalea from this locality as
Rhododendron indicum
var.
mikawanum
in 1909.
(2)
E. H. Wilson treated the Ashitaka azalea as a new combination,
Rhododendron obtusum
var.
kaempferi
f.
mikawanum
, arguing that the increase in number of stamens from 5 to 10 "is another instance of the extraordinary range of variation that obtains in
R. obtusum
.
(3)
"
Rhododendron komiyamae
is a much-branched shrub, growing to 2 meters. The leaves are persistent to the same degree as
R. kaempferi
and clothed with appressed brown hairs on the upper and lower surfaces. The flowers of
R. komiyamae
appear before the leaves, or nearly so, and are borne in terminal clusters of 1 to 4. The corolla is reddish purple, 2 to 3.5 cm. across. The stamens of
R. komiyamae
number 10 and this is the chief characteristic that distinguishes
R. komiyamae
from
R. kaempferi
. The latter species has 5 stamens.
At first, one might attribute nothing unusual about
R. komiyamae
except that it is a new entity. Next to
R. kaempferi
, it is the most northern of the large evergreen azaleas of Japan. From this standpoint,
R. komiyamae
should be a most useful parent for breeding purposes.
The hybrid populations at Ashitaka are a significant example of the manner in which the widely distributed
R. kaempferi
hybridizes naturally with local species.
R. kaempferi
occurs from southern Kyushu to central Hokkaido, a distribution which far exceeds that of any other azalea of Japan. In doing so,
R. kaempferi
hybridizes and produces hybrid populations with local species encountered. This occurs at Mt. Kirishima in Kyushu where there are hybrid populations between
R. kaempferi
and
R. kiusianum
.
The same situation occurs where
R. kaempferi
and
R. macrosepalum
grow together in colonies near Ikeda and Miyakoda, Honshu. This hybrid is called R. x tectum.
At Mt. Ashitaka, it is possible to observe a similar relationship between
R. kaempferi
and
komiyamae
.
R.kaempferi
occurs near Jurigi village, up to 900 meters elevation.
R. komiyamae
occurs at the summit of Mt. Ashitaka (Eichizen-dake) at 1500 meters. Between the two localities and particularly on moist mossy hummocks where seedlings have a better chance to survive, a bewildering array of seedlings can be found. These range in flower color from pink to purple and have between 5 and 10 stamens. These are natural hybrid populations between
R. kaempferi
and
R. komiyamae
and probably the entity which Wilson chose to call
R. obtusum
var.
kaempferi
f.
mikawanum
.
For those who would like to visit this interesting habitat, it can be reached easily from Tokyo. The express bus takes one from Tokyo around Mt. Fuji to Gotemba in about 3 hours. A one-half hour car trip or taxi will bring the visitor to the television signal station at the foot of Mt. Ashitaka. The climb from 900 meters to the top of Ashitaka (1,505 m.) requires about 3 hours. The trail leads through a veritable sea of shoulder-high Sasa bamboo but this is soon reduced to knee-height at a clearing around 1,100 meters. One can obtain exciting views of Mt. Fuji from this spot. The hillsides are covered with colonies of
Ilex crenata
,
Pieris japonica
,
Ligustrum japonicum
,
Stewartia
,
Rosa,
and
Deutzia
as well as pines and Hinoki cypress. At the top, under the usual cool, foggy conditions that typify Japanese volcanic cones,
R. komiyame
is abundantly scattered across the summit of Mt. Ashitaka.
Literature Cited
1. Makino, T., 1926, A contribution to the knowledge of the flora of Japan, Jour. Jap. Bot., lll, No. 5.
2. Makino, T, 1909, Rhododendron indicum var. mikawanum, In Tokyo Bot. Mag., XXIII, 251.
3. Wilson, E. H., and Alfred Rehder, 1921, A monograph of azalea, The University Press, Cambridge.