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Useful Temperate Plants

Rhododendron maximum

L.

Ericaceae

+ Synonyms

Rhododendron ashleyi Coker

Common Name: Rosebay Rhododendron

No Image.

General Information

Rhododendron maximum is an evergreen shrub or small tree that can be as small as 1 metres in the north of its range, but up to 12 metres in the south. Larger specimens can form a crooked trunk up to 30cm in diameter and heavy, contorted branches. Several stems can grow from the root crown[
1050
Title
Fire Effects Information System
Publication
 
Author
 
Website
http://www.feis-crs.org/feis/
Publisher
 
Year
0
ISBN
 
Description
An on-line information site with comprehensive information on over 1,100 species of plant. Mainly developed to supply information on the effects of fire on plants and animals, it also contains a wealth of other information on the plants
].
The plant is harvested from the wild for local use as a medicine and source of materials. It is sometimes grown as an ornamental in gardens.
Rhododendron maximum has a very wide distribution, a large population, is not currently experiencing any major
threats and no significant future threats have been identified. The plant is classified as 'Least Concern' in the IUCN Red List of Threatened Species(2018)[
338
Title
IUCN Red List of Threatened Species
Publication
 
Author
 
Website
http://www.iucnredlist.org/
Publisher
 
Year
0
ISBN
 
Description
A list of plants under threat and facing possible extinction, usually with brief details of the threats and information on habitat.
].
The plant is increasing its range in eastern N. America, where it can form dense thickets that exclude other plants and reduce the diversity in the forest. It can also prevent regeneration of canopy trees and so has the potential to become a weed[
1050
Title
Fire Effects Information System
Publication
 
Author
 
Website
http://www.feis-crs.org/feis/
Publisher
 
Year
0
ISBN
 
Description
An on-line information site with comprehensive information on over 1,100 species of plant. Mainly developed to supply information on the effects of fire on plants and animals, it also contains a wealth of other information on the plants
]..

Known Hazards

The leaves are poisonous[
222
Title
A Field Guide to Medicinal Plants. Eastern and Central N. America.
Publication
 
Author
Foster. S. & Duke. J. A.
Publisher
Houghton Mifflin Co.
Year
1990
ISBN
0395467225
Description
A concise book dealing with almost 500 species. A line drawing of each plant is included plus colour photographs of about 100 species. Very good as a field guide, it only gives brief details about the plants medicinal properties.
]. Ingestion can cause convulsions and coma[
222
Title
A Field Guide to Medicinal Plants. Eastern and Central N. America.
Publication
 
Author
Foster. S. & Duke. J. A.
Publisher
Houghton Mifflin Co.
Year
1990
ISBN
0395467225
Description
A concise book dealing with almost 500 species. A line drawing of each plant is included plus colour photographs of about 100 species. Very good as a field guide, it only gives brief details about the plants medicinal properties.
].
Although no other 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.
,
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.
,
270
Title
Flora of N. America
Publication
 
Author
 
Website
http://flora.huh.harvard.edu/fna/
Publisher
 
Year
0
ISBN
 
Description
An on-line version of the flora with an excellent description of the plant including a brief mention of plant uses.

Range

Eastern N. America - New York to Maine, south to Alabama and Georgia

Habitat

Damp places along streams, edges of bogs and ponds, woods and mountain slopes to 900 metres[
43
Title
Gray's Manual of Botany.Eighth Edition
Publication
 
Author
Fernald. M. L.
Publisher
American Book Co.; New York
Year
1950
ISBN
0442222505
Description
A bit dated but a good and concise flora of the eastern part of N. America.
,
184
Title
Shrubs.
Publication
 
Author
Phillips. R. & Rix. M.
Publisher
Pan Books
Year
1989
ISBN
0-330-30258-2
Description
Excellent photographs and a terse description of 1,900 species and cultivars.
], often forming impenetrable thickets[
235
Title
An Illustrated Flora of the Northern United States and Canada
Publication
 
Author
Britton. N. L. Brown. A.
Publisher
Dover Publications. New York.
Year
1970
ISBN
0-486-22642-5
Description
Reprint of a 1913 Flora, but still a very useful book.
].

Properties

Weed PotentialYes
Conservation StatusLeast Concern
Medicinal Rating *  *
Other Uses Rating *  *
HabitEvergreen Shrub
Height3.50 m
PollinatorsBees, Insects
Cultivation StatusWild

Cultivation Details

Rhododendron maximum is a very cold-hardy plant, able to tolerate temperatures down to around -30°c when fully dormant[
184
Title
Shrubs.
Publication
 
Author
Phillips. R. & Rix. M.
Publisher
Pan Books
Year
1989
ISBN
0-330-30258-2
Description
Excellent photographs and a terse description of 1,900 species and cultivars.
,
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.
]. 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]).
].
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

None known

Medicinal

Some caution is advised in the medicinal usage of this plant - see the notes above on toxicity.

The poulticed leaves are used to relieve arthritic pain, headaches etc[
61
Title
A Dictionary of Plants Used by Man.
Publication
 
Author
Usher. G.
Publisher
Constable
Year
1974
ISBN
0094579202
Description
Forget the sexist title, this is one of the best books on the subject. Lists a very extensive range of useful plants from around the world with very brief details of the uses. Not for the casual reader.
,
222
Title
A Field Guide to Medicinal Plants. Eastern and Central N. America.
Publication
 
Author
Foster. S. & Duke. J. A.
Publisher
Houghton Mifflin Co.
Year
1990
ISBN
0395467225
Description
A concise book dealing with almost 500 species. A line drawing of each plant is included plus colour photographs of about 100 species. Very good as a field guide, it only gives brief details about the plants medicinal properties.
]. A decoction of the leaves is occasionally employed internally in domestic practice in the treatment of rheumatism[
82
Title
Manual of the Trees of N. America.
Publication
 
Author
Sargent. C. S.
Website
http://www.biodiversitylibrary.org/
Publisher
Dover Publications Inc. New York.
Year
1965
ISBN
0-486-20278-X
Description
Two volumes, a comprehensive listing of N. American trees though a bit out of date now. Good details on habitats, some details on plant uses. Not really for the casual reader. It can be downloaded from the internet.
,
257
Title
Native American Ethnobotany
Publication
 
Author
Moerman. D.
Publisher
Timber Press. Oregon.
Year
1998
ISBN
0-88192-453-9
Description
Very comprehensive but terse guide to the native uses of plants. Excellent bibliography, fully referenced to each plant, giving a pathway to further information. Not for the casual reader.
].
The leaves are taken internally in controlled dosage for the treatment of heart ailments[
222
Title
A Field Guide to Medicinal Plants. Eastern and Central N. America.
Publication
 
Author
Foster. S. & Duke. J. A.
Publisher
Houghton Mifflin Co.
Year
1990
ISBN
0395467225
Description
A concise book dealing with almost 500 species. A line drawing of each plant is included plus colour photographs of about 100 species. Very good as a field guide, it only gives brief details about the plants medicinal properties.
].
Caution is advised, see the notes above on toxicity.

Agroforestry Uses:

The large, leathery leaves can be up to 35cm long. They are retained for up to 8 years, and once shed, are slow to decompose, providing a good material for mulching acid-loving plants[
1050
Title
Fire Effects Information System
Publication
 
Author
 
Website
http://www.feis-crs.org/feis/
Publisher
 
Year
0
ISBN
 
Description
An on-line information site with comprehensive information on over 1,100 species of plant. Mainly developed to supply information on the effects of fire on plants and animals, it also contains a wealth of other information on the plants
,
K
Title
Plants for a Future
Author
Ken Fern
Description
Notes from observations, tasting etc at Plants For A Future and on field trips.
].

Other Uses

Wood - fine-grained, hard, heavy, strong, rather brittle[
46
Title
Dictionary of Economic Plants.
Publication
 
Author
Uphof. J. C. Th.
Publisher
Weinheim
Year
1959
ISBN
-
Description
An excellent and very comprehensive guide but it only gives very short descriptions of the uses without any details of how to utilize the plants. Not for the casual reader.
,
61
Title
A Dictionary of Plants Used by Man.
Publication
 
Author
Usher. G.
Publisher
Constable
Year
1974
ISBN
0094579202
Description
Forget the sexist title, this is one of the best books on the subject. Lists a very extensive range of useful plants from around the world with very brief details of the uses. Not for the casual reader.
,
82
Title
Manual of the Trees of N. America.
Publication
 
Author
Sargent. C. S.
Website
http://www.biodiversitylibrary.org/
Publisher
Dover Publications Inc. New York.
Year
1965
ISBN
0-486-20278-X
Description
Two volumes, a comprehensive listing of N. American trees though a bit out of date now. Good details on habitats, some details on plant uses. Not really for the casual reader. It can be downloaded from the internet.
,
229
Title
The Complete Trees of N. America. Field Guide and Natural History.
Publication
 
Author
Elias. T.
Publisher
Van Nostrand Reinhold Co.
Year
1980
ISBN
0442238622
Description
A very good concise guide. Gives habitats, good descriptions, maps showing distribution and a few of the uses. It also includes the many shrubs that occasionally reach tree proportions.
]. It weighs 39lb per cubic foot[
235
Title
An Illustrated Flora of the Northern United States and Canada
Publication
 
Author
Britton. N. L. Brown. A.
Publisher
Dover Publications. New York.
Year
1970
ISBN
0-486-22642-5
Description
Reprint of a 1913 Flora, but still a very useful book.
]. Used for tool handles and as a boxwood (Buxus spp.) substitute in engraving[
46
Title
Dictionary of Economic Plants.
Publication
 
Author
Uphof. J. C. Th.
Publisher
Weinheim
Year
1959
ISBN
-
Description
An excellent and very comprehensive guide but it only gives very short descriptions of the uses without any details of how to utilize the plants. Not for the casual reader.
,
61
Title
A Dictionary of Plants Used by Man.
Publication
 
Author
Usher. G.
Publisher
Constable
Year
1974
ISBN
0094579202
Description
Forget the sexist title, this is one of the best books on the subject. Lists a very extensive range of useful plants from around the world with very brief details of the uses. Not for the casual reader.
,
82
Title
Manual of the Trees of N. America.
Publication
 
Author
Sargent. C. S.
Website
http://www.biodiversitylibrary.org/
Publisher
Dover Publications Inc. New York.
Year
1965
ISBN
0-486-20278-X
Description
Two volumes, a comprehensive listing of N. American trees though a bit out of date now. Good details on habitats, some details on plant uses. Not really for the casual reader. It can be downloaded from the internet.
,
229
Title
The Complete Trees of N. America. Field Guide and Natural History.
Publication
 
Author
Elias. T.
Publisher
Van Nostrand Reinhold Co.
Year
1980
ISBN
0442238622
Description
A very good concise guide. Gives habitats, good descriptions, maps showing distribution and a few of the uses. It also includes the many shrubs that occasionally reach tree proportions.
].

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. 2019-09-20. <temperate.theferns.info/plant/Rhododendron+maximum>

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