Rhododendron amagianum • Mt. Amagi azalea

Rhododendron • Rhododendron / Azalea • シャクナゲ / ツツジ • 石楠花 / 躑躅 • shakunage / tsutsuji

Somehow R. amagianum was accidentally dropped from the newer editions of the Plant List, until our senior gardener Patty spotted it blooming on the mountain side of area Y this year. Its interesting clusters of three-leaves (Danish Chapter of ARS lists it as closely closely related to R. reticulatum, which is also trifoliatum – see link below) and bright red blossoms also called visitors’ attention and resulted in questions about the plant; Corinne and Maggie at the Plant Committee confirmed that Kathleen Smith had it listed in her rhododendron binders and the last Plant List she worked on (2008), exactly where it grows….

Corinne found info that it is evergreen, while Maggie’s sources described it as deciduous – as you can see below  Hirsutum (international on-line rhododendron project) and Learn2grow (educational on-line gardening resource) also disagree on this matter… Perhaps  it depends on the climate it grows under certain circumstances? An article by K. Wada from 1974 which discusses hybridizing evergreen azaleas  may shed some light on this discrepancy of information and mentions this particular plant (last link in the post below)…


SJG • 6/14/14 – Rhododendron amagianum • Mt. Amagi azalea, Area Y, close to the Service Road (you can see it behind the plant)


SJG • 6/14/14 – Rhododendron amagianum • Mt. Amagi azalea, Area Y – Flowers and tri-leaf

From HirsutumR. amagianum
In cultivation since: 1930
First described: 1930, (Makino)
Origin: Mts Amagi and Higane in Idzu Province, S Honshu, Japan
Corolla: openly campanulate
Leaves: broadly ovate
Habit: terrestrial
Winter: evergreen
Bloomtime: very late
Hardiness: H4
Predominant color: orange
Height : 500 cm. (17ft.)

From Learn2Grow: […] Rounded leaves are an interesting foil behind the fuchsia-orange flowers in early summer on Rhododendron amagianum, the Mt. Amagi azalea. Native to the Japanese island of Honshu, it is endangered as the decidous woodlands in which it grows are becoming more scarce. This upright deciduous shrub has a slightly spreading shape. In a garden setting it is slow to produce flowers until well-established and aged.

Whorled clusters of three rounded rhombus-shaped leaves are found at branch tips. The leaf is emerald green and thin. In late spring or early summer, a one to three numbers clusterd of non-fragrant blooms appear on branch tips above the leaves. Each flower is fuchsia-rose, but significant hints of salmon-orange are present, too. On some plants the flowers can be red-orange or fully red. […]

Google translation of the Danish Chapter of ARS for the plant  also think it’s deciduous: […] R. amagianum ( Brachycalyx ) is one of the late-flowering species and is closely related to R. reticulatum. Grows upright to a tall shrub. Leaves sitting in rosettes on 3 Deciduous. Both originated from Japan. […]

American Rhododendron Society also lists R. amagianum as deciduous.

K. Wada, Yokohama, Japan: […]  Azalea R. poukhanense, belongs to the Azalea Obtusum Subseries but is deciduous to withstand the most rigorous winter temperatures. Some forms of Kaempferi azalea of the most northerly distribution are made nearly deciduous from the same winter temperatures. Nobody would deny the tri-foliated deciduous azaleas must have some physical body structure that can stand lower winter temperatures than evergreen azaleas. If the more winter hardly constitution of the trifoliate azalea group can be bred into the present Southern Indica hybrid azaleas, some of the progeny may be hardier, have the original large flowers and may grow satisfactorily in colder climates. Thus a new strain of larger flowers combined with more winter hardiness may be established. I suggest that the azalea R. amagianum, with large brick to orange-red flowers of the tri-foliated group might be used for this purpose. For your information, the R. amagianum plants gave plenty of seedlings with evergreen foliage when crossed with large-flowering evergreen azalea R. sublanceolatum and some of the seedlings may be as hardy as R. amagianum with flowers as large as R. sublanceolatum. R. sublanceolatum and its relatives are native to the most southerly part of Japan and were an important parent of the present Southern Indica hybrids. […]

Thank you Kathleen Smith – your enormous body of work on SJG plants and materials you gifted our Plant Committee with,  guide us still.


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