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Useful Temperate Plants

Rhododendron indicum

(L.) Sweet

Ericaceae

+ Synonyms

Azalea burgeri Miq.

Azalea calycina Lem.

Azalea crispiflora Hook.

Azalea danielsiana Paxton

Azalea decumbens (D.Don ex G.Don) DC.

Azalea indica L.

Azalea macrantha Bunge

Azalea obtusa Lindl.

Enkianthus biflorus Lour.

Loiseleria indica Rchb.

Rhododendron breynii Planch.

Rhododendron danielsianum Planch.

Rhododendron decumbens D.Don ex G.Don

Rhododendron hannoense Nakai

Rhododendron lateritium Planch.

Rhododendron macranthum (Bunge) G.Don

Rhododendron obtusum (Lindl.) Planch.

Common Name:

No Image.

General Information

Rhododendron indicum is a much-branched evergreen or semi-evergreen shrub that can grow 90 - 200cm tall, though sometimes it is low and more or less prostrate[
275
Title
Flora of Japan
Publication
 
Author
 
Website
http://www.foj.info
Publisher
 
Year
0
ISBN
 
Description
An on-line version of the flora - an excellent resource.
]
The plant is harvested from the wild for local use as a food and source of materials. It is an ingredient of commercial cosmetic preparations and is also grown as an ornamental in gardens, where it can be used to form a ground cover.

Known Hazards

Although no specific mention of toxicity has been seen for this species, all parts of Rhododendron species (including the leaves, flowers and pollen) contain greater or lesser amounts of the toxic compound andromedotoxin (also known as grayanotoxin). Rarely lethal to humans (and used medicinally in some herbal disciplines), this compound causes dose-dependant overstimulation of the central nervous system with symptoms including various cardiovascular effects (mainly low blood pressure and cardiac rhythm disorders); nausea and vomiting; and a change in consciousness. The effects commence shortly after ingestion and last around two days. These effects are also transferred to honey made from the nectar of the flowers. In some parts of the world bees are used to deliberately produce a honey rich in andromedotoxin which is then eaten for its supposed medicinal, hallucinogenic and aphrodisiac effects.
In contrast to humans, many other creatures are more susceptible to the toxin and it has sometimes proved lethal to grazing animals and household pets. Some forms of honeybees are also killed by the toxin (resistant forms of the bee are used for honey production). Bumblebees are not affected, however, and are also more efficient in pollinating rhododendron flowers, so one theory is that the toxin is produced by the plant in order to favour the bumblebee and improve fertilization rates[
1668
Title
Grayanotoxin Poisoning: ‘Mad Honey Disease’ and Beyond
Publication
Cardiovasc Toxicol (2012) 12:208-215
Author
Jansen S.A. et al
Website
https://doi.org/10.1007/s12012-012-9162-2
Publisher
 
Year
2012
ISBN
 
Description
An in-depth review of the literature on the toxic effects of a toxin widely found in the family Ericaceae
].

Botanical References

11
Title
Trees and Shrubs Hardy in Great Britain. Vol 1 - 4 and Supplement.
Publication
 
Author
Bean. W.
Publisher
Murray
Year
1981
ISBN
-
Description
A classic with a wealth of information on the plants, but poor on pictures.
,
58
Title
Flora of Japan. (English translation)
Publication
 
Author
Ohwi. G.
Publisher
Smithsonian Institution
Year
1965
ISBN
-
Description
The standard work. Brilliant, but not for the casual reader.
,
200
Title
The New RHS Dictionary of Gardening. 1992.
Publication
 
Author
Huxley. A.
Publisher
MacMillan Press
Year
1992
ISBN
0-333-47494-5
Description
Excellent and very comprehensive, though it contains a number of silly mistakes. Readable yet also very detailed.

Range

E. Asia - central and southern Japan.

Habitat

Rocks in ravines[
58
Title
Flora of Japan. (English translation)
Publication
 
Author
Ohwi. G.
Publisher
Smithsonian Institution
Year
1965
ISBN
-
Description
The standard work. Brilliant, but not for the casual reader.
]. Sunny rocks along rivers; at elevations from 60 - 1,100 metres[
275
Title
Flora of Japan
Publication
 
Author
 
Website
http://www.foj.info
Publisher
 
Year
0
ISBN
 
Description
An on-line version of the flora - an excellent resource.
].

Properties

Edibility Rating *
Other Uses Rating *  *
HabitEvergreen Shrub
Height1.00 m
PollinatorsInsects
Cultivation StatusOrnamental, Wild

Cultivation Details

Rhododendron indicum is native to the warm temperate zone of southern Japan, where it can be found at elevations up to 1,100 metres. Somewhat variable in cold-tolerance, when fully dormant that are some forms that can withstand temperatures down to about -20°c. Although cold-tolerant when dormant, the flowers and young growth of Rhododendrons are very susceptible to damage by late frosts in regions where these are likely to occur after new growth has commenced in the spring[
200
Title
The New RHS Dictionary of Gardening. 1992.
Publication
 
Author
Huxley. A.
Publisher
MacMillan Press
Year
1992
ISBN
0-333-47494-5
Description
Excellent and very comprehensive, though it contains a number of silly mistakes. Readable yet also very detailed.
].
Succeeds in a most humus-rich lime-free soils except those of a dry arid nature or those that are heavy or clayey[
1
Title
RHS Dictionary of Plants plus Supplement. 1956
Publication
 
Author
F. Chittendon.
Publisher
Oxford University Press
Year
1951
ISBN
-
Description
Comprehensive listing of species and how to grow them. Somewhat outdated, it has been replaced in 1992 by a new dictionary (see [200]).
]. Prefers a peaty or well-drained sandy loam[
1
Title
RHS Dictionary of Plants plus Supplement. 1956
Publication
 
Author
F. Chittendon.
Publisher
Oxford University Press
Year
1951
ISBN
-
Description
Comprehensive listing of species and how to grow them. Somewhat outdated, it has been replaced in 1992 by a new dictionary (see [200]).
]. Succeeds in sun or shade, the warmer the climate the more shade a plant requires[
200
Title
The New RHS Dictionary of Gardening. 1992.
Publication
 
Author
Huxley. A.
Publisher
MacMillan Press
Year
1992
ISBN
0-333-47494-5
Description
Excellent and very comprehensive, though it contains a number of silly mistakes. Readable yet also very detailed.
]. A pH between 4.5 and 5.5 is ideal[
1
Title
RHS Dictionary of Plants plus Supplement. 1956
Publication
 
Author
F. Chittendon.
Publisher
Oxford University Press
Year
1951
ISBN
-
Description
Comprehensive listing of species and how to grow them. Somewhat outdated, it has been replaced in 1992 by a new dictionary (see [200]).
].
Plants do not succeed in all parts of Britain, they are hardy by the coast and succeed in warmer gardens inland[
1
Title
RHS Dictionary of Plants plus Supplement. 1956
Publication
 
Author
F. Chittendon.
Publisher
Oxford University Press
Year
1951
ISBN
-
Description
Comprehensive listing of species and how to grow them. Somewhat outdated, it has been replaced in 1992 by a new dictionary (see [200]).
].
Succeeds in a woodland though, because of its surface-rooting habit[
200
Title
The New RHS Dictionary of Gardening. 1992.
Publication
 
Author
Huxley. A.
Publisher
MacMillan Press
Year
1992
ISBN
0-333-47494-5
Description
Excellent and very comprehensive, though it contains a number of silly mistakes. Readable yet also very detailed.
], it does not compete well with surface-rooting trees[
1
Title
RHS Dictionary of Plants plus Supplement. 1956
Publication
 
Author
F. Chittendon.
Publisher
Oxford University Press
Year
1951
ISBN
-
Description
Comprehensive listing of species and how to grow them. Somewhat outdated, it has been replaced in 1992 by a new dictionary (see [200]).
]. Plants need to be kept well weeded, they dislike other plants growing over or into their root system, in particular they grow badly with ground cover plants, herbaceous plants and heathers[
200
Title
The New RHS Dictionary of Gardening. 1992.
Publication
 
Author
Huxley. A.
Publisher
MacMillan Press
Year
1992
ISBN
0-333-47494-5
Description
Excellent and very comprehensive, though it contains a number of silly mistakes. Readable yet also very detailed.
].
Plants form a root ball and are very tolerant of being transplanted, even when quite large, so long as the root ball is kept intact[
200
Title
The New RHS Dictionary of Gardening. 1992.
Publication
 
Author
Huxley. A.
Publisher
MacMillan Press
Year
1992
ISBN
0-333-47494-5
Description
Excellent and very comprehensive, though it contains a number of silly mistakes. Readable yet also very detailed.
].
Plants in this genus are notably susceptible to honey fungus[
200
Title
The New RHS Dictionary of Gardening. 1992.
Publication
 
Author
Huxley. A.
Publisher
MacMillan Press
Year
1992
ISBN
0-333-47494-5
Description
Excellent and very comprehensive, though it contains a number of silly mistakes. Readable yet also very detailed.
].

Edible Uses

Flowers[
105
Title
Tanaka's Cyclopedia of Edible Plants of the World.
Publication
 
Author
Tanaka. T. & Nakao S.
Publisher
Keigaku Publishing; Tokyo
Year
1976
ISBN
-
Description
The most comprehensive list of edible plants I've come across. Only the briefest entry for each species, though, and some of the entries are more than a little dubious. Not for the casual reader.
,
177
Title
Plants for Human Consumption
Publication
 
Author
Kunkel. G.
Publisher
Koeltz Scientific Books
Year
1984
ISBN
3874292169
Description
An excellent book for the dedicated. A comprehensive listing of Latin names with a brief list of edible parts.
,
183
Title
Cornucopia - A Source Book of Edible Plants.
Publication
 
Author
Facciola. S.
Publisher
Kampong Publications
Year
1990
ISBN
0-9628087-0-9
Description
Excellent. Contains a very wide range of conventional and unconventional food plants (including tropical) and where they can be obtained (mainly N. American nurseries but also research institutes and a lot of other nurseries from around the world.
]. No further details are given but some caution is advised, see the notes above on toxicity.

Leaves[
105
Title
Tanaka's Cyclopedia of Edible Plants of the World.
Publication
 
Author
Tanaka. T. & Nakao S.
Publisher
Keigaku Publishing; Tokyo
Year
1976
ISBN
-
Description
The most comprehensive list of edible plants I've come across. Only the briefest entry for each species, though, and some of the entries are more than a little dubious. Not for the casual reader.
,
177
Title
Plants for Human Consumption
Publication
 
Author
Kunkel. G.
Publisher
Koeltz Scientific Books
Year
1984
ISBN
3874292169
Description
An excellent book for the dedicated. A comprehensive listing of Latin names with a brief list of edible parts.
,
183
Title
Cornucopia - A Source Book of Edible Plants.
Publication
 
Author
Facciola. S.
Publisher
Kampong Publications
Year
1990
ISBN
0-9628087-0-9
Description
Excellent. Contains a very wide range of conventional and unconventional food plants (including tropical) and where they can be obtained (mainly N. American nurseries but also research institutes and a lot of other nurseries from around the world.
]. No further details are given but some caution is advised, see the notes above on toxicity.

The galls on the leaves are also said to be edible[
177
Title
Plants for Human Consumption
Publication
 
Author
Kunkel. G.
Publisher
Koeltz Scientific Books
Year
1984
ISBN
3874292169
Description
An excellent book for the dedicated. A comprehensive listing of Latin names with a brief list of edible parts.
]. The report does not say if the galls are eaten before or after the insect has left. Caution is advised, see notes above on toxicity.

Medicinal

None known

Agroforestry Uses:

Low-growing forms of this species can be grown as ground cover when spaced about 1 metre apart each way[
208
Title
Plants for Ground Cover
Publication
 
Author
Thomas. G. S.
Publisher
J. M. Dent & Sons
Year
1990
ISBN
0-460-12609-1
Description
An excellent detailled book on the subject, very comprehensive.
].

Other Uses

An extract of the flowers is used as an ingredient in commercial cosmetic preparations as a skin conditioner[
1243
Title
CosIng
Publication
 
Author
 
Website
http://ec.europa.eu/growth/tools-databases/cosing/
Publisher
 
Year
0
ISBN
 
Description
CosIng is the European Commission database for information on cosmetic substances and ingredients.
].

Propagation

Seed - best sown in a greenhouse as soon as it is ripe in the autumn and given artificial light. Alternatively sow the seed in a lightly shaded part of the warm greenhouse in late winter or in a cold greenhouse in mid spring. Surface-sow the seed and do not allow the compost to become dry[
200
Title
The New RHS Dictionary of Gardening. 1992.
Publication
 
Author
Huxley. A.
Publisher
MacMillan Press
Year
1992
ISBN
0-333-47494-5
Description
Excellent and very comprehensive, though it contains a number of silly mistakes. Readable yet also very detailed.
]. Pot up the seedlings when they are large enough to handle and grow on in a greenhouse for at least the first winter.
Layering in late July. Takes 15 - 24 months[
78
Title
Propagation of Trees, Shrubs and Conifers.
Publication
 
Author
Sheat. W. G.
Publisher
MacMillan and Co
Year
1948
ISBN
-
Description
A bit dated but a good book on propagation techniques with specific details for a wide range of plants.
].
Cuttings of half-ripe wood, August in a frame. Difficult[
78
Title
Propagation of Trees, Shrubs and Conifers.
Publication
 
Author
Sheat. W. G.
Publisher
MacMillan and Co
Year
1948
ISBN
-
Description
A bit dated but a good book on propagation techniques with specific details for a wide range of plants.
].
Cite as: Temperate Plants Database, Ken Fern. temperate.theferns.info. 2019-12-08. <temperate.theferns.info/plant/Rhododendron+indicum>

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