Species In Our
Rhododendron kaempferi is commonly called the Torch or Kaempfer azalea; in Japan it is called 'Yama Tsutsuji'. R. kaempferi is in the subgenus Tsutsusi, a large section of evergreen azalea species. It is the most common azalea of Japan being found from the southern island of Kyushu to the northern island of Hokkaido from sea level to 4000 feet (1200 m) elevation. At home on volcanic slopes, open shrubland and in mixed deciduous forests this evergreen azalea is an upright growing shrub to 8 feet (3 m) in height.
Like many evergreen azaleas it produces 2 kinds of leaves, spring leaves and summer leaves. It is the summer leaves that will survive the winter, with the spring leaves being deciduous. The spring leaves are narrowly lance-shaped 1-1.5 inch (2-3 cm) long with ciliated margins and scattered bristles on the upper and lower surfaces. The smaller summer leaves 1/4 to 3/4 inch (1 to 1.8 cm) long are similarly hairy and clustered around the terminal bud. The young shoots are covered with adpressed flattened chestnut-brown hairs.
There are 2 to 3 flowers in the inflorescence, which has a pedicel of dense brown strigose hairs as does the 0.1-0.2 inch (3-5 mm) long calyx. The red corolla is broadly funnel-shaped 1- 1.5 inches (20-30 mm) long with the tube 1/2 the length of the corolla and glabrous (hairless) as well as eglandular (without glands). The 5 stamens extend to or slightly beyond the corolla with soft hairs on the lower half. The ovary and the mature seed capsule are covered with adpressed shiny brown hairs.
Although the red flower is considered the typed specimen there are lovely salmon colors in northern Japan described as Latisepalum Group. Pink and white flower forms have also been selected from the wild. Natural hybrids with R. kiusianum occur wherever their habitats overlap. In fact, E. H. Wilson described a continuum of kaempferi and kiusianum hybrids as he explored one mountain in Japan. There is, in the more southerly locations, a natural hybrid with the pollen parent R. macrosepalum which has the larger flower and calyx of macrosepalum with the adpressed hairs along the new shoots as in R. kaempferi and it has been given the name R. x transiens.
Named to honor a Dutch Merchant Englebert Kaempfer who illustrated it in his book Amoenitates Exoticase, published in 1712, R. kaempferi was not introduced to the West until C.S. Sargent imported seeds in 1892 to the Arnold Arboretum. When it flowered in May of 1897 it quickly became a popular cultivated plant in the west. A number of synonym names can be found in older references such as Azalea kaempferi, 'Tsutsusi', R. sieboldii, R. macrogemmumin, R. obtusum var. kaempferi.
The Arnold Arboretum in early to mid-May is the place to visit for R. kaempferi bloom. Whether the groups of kaempferi there are descendants of the original imported seed or from later exchanges, there is a wonderful array of colors in mature plants. Other places that I like to visit are Maudsley State Park Newburyport, MA and the Cochran Bird Sanctuary in Andover, MA both having a similar assortment of R. kaempferi or their hybrids. The tall stately plants give an airy color to a deciduous woodland setting. The deciduous nature of the spring leaves can add another season of interest in the colder climates. Plants in at least 1/2 day sun will produce fall color nicely in yellow, orange and red.
I can hardly do justice to the multitudes of hybrids that have used R. kaempferi in its breeding, except to point out that it has been an important gene component to the development of evergreen azalea hybrids. I would not be surprised to find the best still in Japan where interesting selections of hose-in-hose, double, and apetaloid forms have been highly sought after. The apetaloid form kinishibe is particularly strange but it has a longer season of color coming from just the golden red stamens.
R. kaempferi hybridization was extensive by P. M. Koster and C. B. vanNes and Sons both of Boskoop Netherlands in the early 1900's. Further hybridization in the United States have resulted in the Kaempferi Hybrids. They are progeny of the cross of kaempferi x 'Malvatica' and resulted in plants like 'Betty' (orange pink), 'Cleopatra' (lilac rose), 'Fedora' (deep pink), 'Willy' ( bright pink) and 'Wilhelmina Vuyk' (white). Joseph Gable in Stewartstown, Pennsylvania used R. kaempferi in his breeding program. He selected the salmon pink 'Indian Summer' for its particularly late bloom.
I grow 4 forms of R. kaempferi and always seem to think I should have more. They all have been perfectly hardy for me in Salem, NH, which by the latest USDA map is now zone 6. I particularly like 'Kesa' a lovely pink, f. semiflorens with its pink stamens and pink strap like petals and f. leucanthum RSF 81/095 a pure white form.
Rated at USDA Zone 5b-8, R. kaempferi is an outstanding species in its own right deserving a place in any woodland garden or even sunny gardens in New England. Free blooming and heat tolerant, remember when planting that the flowers can fade, especially the lovely salmon flower color. So site it out of the hot afternoon sun.
Locally Weston Nursery has R. kaempferi or hybrids. Named forms are available from the Rhododendron Species Foundation such as the RSF 1977/659 'Eastern Fire' a strong red form.
Sally Perkins, Salem, NH