Rhododendron maximum
L.
Ericaceae
Rhododendron ashleyi Coker
Common Name: Rosebay Rhododendron
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 Potential | Yes |
Conservation Status | Least Concern |
Medicinal Rating | |
Other Uses Rating | |
Habit | Evergreen Shrub |
Height | 3.50 m |
Pollinators | Bees, Insects |
Cultivation Status | Wild |
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.
].