94,129
edits
Changes
From Gardenology.org - Plant Encyclopedia and Gardening Wiki
Jump to navigationJump to searchNew page: {{Taxobox | name = ''Rhododendron'' | image = rhododendron-by-eiffel-public-domain-20040617.jpg | image_width = 250px | image_caption = ''Rhododendron ponticum'' | regnum = Plantae | d...
{{Taxobox
| name = ''Rhododendron''
| image = rhododendron-by-eiffel-public-domain-20040617.jpg
| image_width = 250px
| image_caption = ''Rhododendron ponticum''
| regnum = [[Plantae]]
| divisio = [[Flowering plant|Magnoliophyta]]
| classis = [[Magnoliopsida]]
| ordo = [[Ericales]]
| familia = [[Ericaceae]]
| genus = '''''Rhododendron'''''
| genus_authority = [[Carolus Linnaeus|L.]]
| subdivision_ranks = Subgenera
| subdivision =
*''[[Rhododendron subgenus Azaleastrum|Azaleastrum]]''
*''[[Rhododendron subgenus Candidastrum|Candidastrum]]''
*''[[Rhododendron subgenus Hymenanthes|Hymenanthes]]''
*''[[Rhododendron subgenus Mumeazalea|Mumeazalea]]''
*''[[Rhododendron subgenus Pentanthera|Pentanthera]]'' ([[Azalea]]s)
*''[[Rhododendron subgenus Rhododendron|Rhododendron]]''
*''[[Rhododendron subgenus Therorhodion|Therorhodion]]''
*''[[Rhododendron subgenus Tsutsusi|Tsutsusi]]'' ([[Azalea]]s)
----
Source: [http://www.rbge.org.uk RBG, Edinburgh]
}}
'''''Rhododendron''''' (from the [[Greek language|Greek]]: ''rhodos'', "rose", and ''dendron'', "tree") is a genus of flowering plants in the family [[Ericaceae]]. It is a large genus with over 1000 [[species]] and most have showy flower displays. It includes the plants known to gardeners as [[azalea]]s. It's the [[national flower]] of [[Nepal]].
The Rhododendron is a genus characterized by [[shrub]]s and small to (rarely) large [[tree]]s, the smallest species growing to 10-100 cm tall, and the largest, ''R. giganteum'', reported to over 30 m tall<ref>[http://wildeel.com/rhodotree.html Tree rhododendrons]</ref>. The [[leaf|leaves]] are spirally arranged; leaf size can range from 1-2 cm to over 50 cm, exceptionally 100 cm in ''R. sinogrande''. They may be either [[evergreen]] or [[deciduous]]. In some species the underside of the leaves is covered with scales (lepidote) or hairs (indumentum). Some of the best known species are noted for their many clusters of large flowers. There are alpine species with small flowers and small leaves, and tropical species such as section ''Vireya'' that often grow as [[epiphyte]]s.
==Distribution==
'''Rhododendron''' is a very widely distributed genus, occurring throughout most of the [[Northern Hemisphere]] except for dry areas, and extending into the [[Southern Hemisphere]] in southeastern [[Asia]] and northern [[Australasia]]. The highest species diversity is found in the [[Himalaya]]n mountains from [[Uttarakhand]], [[Nepal]] and [[Sikkim]] to [[Yunnan]] and [[Sichuan]], with other significant areas of diversity in the mountains of [[Indo-China]], [[Korea]], [[Japan]] and [[Taiwan]]. Rhododendron, also known as "Lali Guras" in local language is the national flower of [[Nepal]] and the state tree of the state of [[Uttarakhand]] in [[India]]. In Korea, [[Rhododendron schlippenbachii]] is particularly common (called 철쭉(choltjuk)). In addition, there are a significant number of tropical rhododendron species from southeast Asia to northern [[Australia]], with 55 known species in [[Borneo]] and 164 in [[New Guinea]]. <ref name="Argent 2006">Argent, G. ''Rhododendrons of subgenus Vireya''. 2006. Royal Horticultural Society. ISBN 1-902896-61-0</ref> Relatively fewer species occur in [[North America]] and [[Europe]]. Rhododendrons have not been found in South America or Africa.
==Classification==
[[Image:Rhododendron wardii var puralbum.jpg|thumb|250px|right|''Rhododendron wardii var. puralbum'']]
The species are organized by subgenus, section, subsection and series. These are currently divided into four large and four small subgenera:
*Subgenus ''Rhododendron'' L.: small leaf or lepidotes (with scales on the underside of their leaves); several hundred species, type: ''[[Rhododendron ferrugineum]]''. The tropical rhododendrons (sect. ''Vireya'', about 300 species) are usually included as a section in this subgenus, but sometimes split off as a ninth subgenus.]]''.
Recent genetic investigations have caused an ongoing realignment of species and groups within the genus, and also have caused the old genus ''[[Ledum]]'' to be reclassified within subgenus ''Rhododendron''. Further realignment within the subgenera is currently proposed <ref name="Goetsch et al.">Goetsch, L. A., Eckert, A. J. & Hall, B. D. (2005). [http://www.ingentaconnect.com/content/aspt/sb/2005/00000030/00000003/art00012 The molecular systematics of Rhododendron (Ericaceae): A Phylogeny based upon RPB2 gene sequences]. ''Sys. Bot''. 30(3): 616-626.</ref><ref>[http://www.flounder.ca/FraserSouth/Goetsch-Eckert-Hall.asp Summary of Goetsch-Eckert-Hall results]</ref>, including the merging of subgenus ''Hymenanthes'' into subgenus ''Pentanthera''.
Rhododendrons are extensively hybridized in cultivation, and natural hybrids often occur in areas where species ranges overlap. There are over 28,000 [[cultivar]]s of Rhododendron in the [http://www.rhs.org.uk/plants/registration_rhododendron.asp International Rhododendron Registry] held by the [[Royal Horticultural Society]]. Most have been bred for their flowers, but a few are of garden interest because of ornamental leaves and some for ornamental bark or stems.
Some species (e.g. ''[[Rhododendron ponticum]]'' in the [[United Kingdom]]) are invasive as introduced plants, spreading in woodland areas replacing the natural understory. R. ponticum is difficult to eradicate, as its roots can make new shoots.
[[Image:Garden with Rhododendrons.JPG|500px|thumb|right|| A garden with tall Rhododendrons in Lynnwood, Washington]]
;Sample species:
*''[[Rhododendron atlanticum]]''
*''[[Rhododendron canadense]]''
*''[[Rhododendron catawbiense]]''
*''[[Rhododendron chapmanii]]''
*''[[Rhododendron ferrugineum]]''
*''[[Rhododendron groenlandicum]]''
*''[[Rhododendron hirsutum]]''
*''[[Rhododendron lochiae]]''
*''[[Rhododendron luteum]]''
*''[[Rhododendron macrophyllum]]''
*''[[Rhododendron maximum]]''
*''[[Rhododendron moulmainense]]''
*''[[Rhododendron occidentale]]''
*''[[Rhododendron ponticum]]''
*''[[Rhododendron schlippenbachii]]''
*''[[Rhododendron spinuliferum]]''
*''[[Rhododendron tomentosum]]''
A sample hybrid:
*[[Rhododendron 'President Roosevelt'|''Rhododendron'' 'President Roosevelt']]
==Toxicology==
<!-- Image with unknown copyright status removed: [[Image:Bee Collecting Pollen From Rhododendron.JPG|500px|thumb|right|| A Bee Collecting Pollen from a Rhododendron Flower]] -->
Some species are poisonous to grazing animals. These Rhododendrons have a [[toxin]] called [[grayanotoxin]] in their [[pollen]] and [[nectar (plant)|nectar]]. People have been known to become ill from eating [[honey]] made by [[bee]]s feeding on rhododendron and azalea flowers. Rhododendron is extremely toxic to horses, with some animals dying within a few hours of ingesting the plant, although most horses tend to avoid it if they have access to good forage.
===Planting and care===
Like other [[Ericaceae|ericaceous]] plants, most rhododendrons prefer acid soils with a pH of roughly 4.5-5.5; some tropical Vireyas and a few other rhododendron species grow as [[epiphyte]]s and require a planting mix similar to [[orchids]]. Rhododendrons have fibrous roots and prefer well-drained soils high in organic material. In areas with poorly-drained or alkaline soils, rhododendrons are often grown in raised beds using mediums such as composted pine bark.<ref>[http://www.rhododendron.org/soil.htm Soil information for planting rhododendrons]</ref> Mulching and careful watering are important, especially before the plant is established.
===Insects and diseases===
{{Main|List of rhododendron diseases}}
There are a number of insects that either target rhododendrons or will opportunistically attack them. Rhododendron borers and various weevils are major pests of rhododendrons, and many caterpillars will attack rhododendrons. Major diseases include ''[[Phytophthora]]'' root rot, stem and twig fungal dieback; [[Ohio State University Extension]] provides [http://www.ag.ohio-state.edu/~ohioline/hyg-fact/3000/3043.html information on maintaining health of rhododendrons]Rhododendrons can easily be suffocated by other plants.
''Rhododendron'' species are used as food plants by the [[larva]]e of some members of the Order [[Lepidoptera]] ([[butterflies]] and [[moths]]) (See [[List of Lepidoptera that feed on rhododendrons]]).
== Gallery ==
<gallery>
Image:Rhododendron decorum ssp diaprepes -1.jpg|''Rhododendron decorum'' subsp. ''diaprepes''
Image:rhododendron2.jpg
Image:Wild Rhododendrons in Kashmir.jpg|Wild Rhododendrons in Kashmir by [[Edward Molyneux]]; painted before 1908
Image:Rhododendron 1 Fcb981.JPG
Image:Wild Rhododendrons in Whitwick Leicestershire 1155.JPG | Flowering Rhododendrons in Whitwick Leicestershire
</gallery>
==Footnotes==
{{reflist}}
==References==
*Cox, P. A. & Kenneth, N. E. ''The Encyclopedia of Rhododendron Species''. 1997. Glendoick Publishing. ISBN 0-9530533-0-X.
*Davidian, H. H. ''The Rhododendron Species''. In four volumes from 1982-1995. Timber Press. ISBN 0-917304-71-3, ISBN 0-88192-109-2, ISBN 0-88192-168-8, ISBN 0-88192-311-7.
==See also==
* [[List of plants poisonous to equines]]
*[[Chinese herbology#50 fundamental herbs|Chinese herbology]] 50 fundamental herbs
==External links==
* [http://en.wikipedia.org/wiki/Rhododendron Wikipedia article]
* [http://www.efloras.org/florataxon.aspx?flora_id=2&taxon_id=128386 Flora of China: ''Rhododendron'']
* [http://www.wfu.edu/~kronka/kakbek/rhododendrons.html Information on rhododendrons at the Ericaceae web pages of Dr. Kron at Wake Forest University.]
* [http://www.vireya.net/ Information on Vireyas]
* [http://www.rhodophiles.com/ Information on Rhododendrons by Marc Colombel, founder of the Société Bretonne du Rhododendron.]
* [http://rhodyman.net/rahome.html Extensive information on rhododendron species: the history of their discovery, botanical details, toxicity, classification, cultural conditions, care for common problems, and suggestions for companion plants by Steve Henning.]
===Rhododendron Societies===
* [http://rhododendron.org/ American Rhododendron Society]
* [http://www.rhs.org.uk/plants/plant_groups/rhododendrons.asp UK Royal Horticultural Society]
* [http://www.rhodygarden.org/ Rhododendron Species Foundation and Botanical Garden]
* [http://honeybee.helsinki.fi/users/avainola/rhodo/club.htm Société Finlandaise du Rhododendron]
* [http://www.eisa.net.au/~mirra/australi.html Australian Rhododendron Society]
* [http://www.rhodo.org/wissen.php?lang=gb German Rhododendron Society]
| name = ''Rhododendron''
| image = rhododendron-by-eiffel-public-domain-20040617.jpg
| image_width = 250px
| image_caption = ''Rhododendron ponticum''
| regnum = [[Plantae]]
| divisio = [[Flowering plant|Magnoliophyta]]
| classis = [[Magnoliopsida]]
| ordo = [[Ericales]]
| familia = [[Ericaceae]]
| genus = '''''Rhododendron'''''
| genus_authority = [[Carolus Linnaeus|L.]]
| subdivision_ranks = Subgenera
| subdivision =
*''[[Rhododendron subgenus Azaleastrum|Azaleastrum]]''
*''[[Rhododendron subgenus Candidastrum|Candidastrum]]''
*''[[Rhododendron subgenus Hymenanthes|Hymenanthes]]''
*''[[Rhododendron subgenus Mumeazalea|Mumeazalea]]''
*''[[Rhododendron subgenus Pentanthera|Pentanthera]]'' ([[Azalea]]s)
*''[[Rhododendron subgenus Rhododendron|Rhododendron]]''
*''[[Rhododendron subgenus Therorhodion|Therorhodion]]''
*''[[Rhododendron subgenus Tsutsusi|Tsutsusi]]'' ([[Azalea]]s)
----
Source: [http://www.rbge.org.uk RBG, Edinburgh]
}}
'''''Rhododendron''''' (from the [[Greek language|Greek]]: ''rhodos'', "rose", and ''dendron'', "tree") is a genus of flowering plants in the family [[Ericaceae]]. It is a large genus with over 1000 [[species]] and most have showy flower displays. It includes the plants known to gardeners as [[azalea]]s. It's the [[national flower]] of [[Nepal]].
The Rhododendron is a genus characterized by [[shrub]]s and small to (rarely) large [[tree]]s, the smallest species growing to 10-100 cm tall, and the largest, ''R. giganteum'', reported to over 30 m tall<ref>[http://wildeel.com/rhodotree.html Tree rhododendrons]</ref>. The [[leaf|leaves]] are spirally arranged; leaf size can range from 1-2 cm to over 50 cm, exceptionally 100 cm in ''R. sinogrande''. They may be either [[evergreen]] or [[deciduous]]. In some species the underside of the leaves is covered with scales (lepidote) or hairs (indumentum). Some of the best known species are noted for their many clusters of large flowers. There are alpine species with small flowers and small leaves, and tropical species such as section ''Vireya'' that often grow as [[epiphyte]]s.
==Distribution==
'''Rhododendron''' is a very widely distributed genus, occurring throughout most of the [[Northern Hemisphere]] except for dry areas, and extending into the [[Southern Hemisphere]] in southeastern [[Asia]] and northern [[Australasia]]. The highest species diversity is found in the [[Himalaya]]n mountains from [[Uttarakhand]], [[Nepal]] and [[Sikkim]] to [[Yunnan]] and [[Sichuan]], with other significant areas of diversity in the mountains of [[Indo-China]], [[Korea]], [[Japan]] and [[Taiwan]]. Rhododendron, also known as "Lali Guras" in local language is the national flower of [[Nepal]] and the state tree of the state of [[Uttarakhand]] in [[India]]. In Korea, [[Rhododendron schlippenbachii]] is particularly common (called 철쭉(choltjuk)). In addition, there are a significant number of tropical rhododendron species from southeast Asia to northern [[Australia]], with 55 known species in [[Borneo]] and 164 in [[New Guinea]]. <ref name="Argent 2006">Argent, G. ''Rhododendrons of subgenus Vireya''. 2006. Royal Horticultural Society. ISBN 1-902896-61-0</ref> Relatively fewer species occur in [[North America]] and [[Europe]]. Rhododendrons have not been found in South America or Africa.
==Classification==
[[Image:Rhododendron wardii var puralbum.jpg|thumb|250px|right|''Rhododendron wardii var. puralbum'']]
The species are organized by subgenus, section, subsection and series. These are currently divided into four large and four small subgenera:
*Subgenus ''Rhododendron'' L.: small leaf or lepidotes (with scales on the underside of their leaves); several hundred species, type: ''[[Rhododendron ferrugineum]]''. The tropical rhododendrons (sect. ''Vireya'', about 300 species) are usually included as a section in this subgenus, but sometimes split off as a ninth subgenus.]]''.
Recent genetic investigations have caused an ongoing realignment of species and groups within the genus, and also have caused the old genus ''[[Ledum]]'' to be reclassified within subgenus ''Rhododendron''. Further realignment within the subgenera is currently proposed <ref name="Goetsch et al.">Goetsch, L. A., Eckert, A. J. & Hall, B. D. (2005). [http://www.ingentaconnect.com/content/aspt/sb/2005/00000030/00000003/art00012 The molecular systematics of Rhododendron (Ericaceae): A Phylogeny based upon RPB2 gene sequences]. ''Sys. Bot''. 30(3): 616-626.</ref><ref>[http://www.flounder.ca/FraserSouth/Goetsch-Eckert-Hall.asp Summary of Goetsch-Eckert-Hall results]</ref>, including the merging of subgenus ''Hymenanthes'' into subgenus ''Pentanthera''.
Rhododendrons are extensively hybridized in cultivation, and natural hybrids often occur in areas where species ranges overlap. There are over 28,000 [[cultivar]]s of Rhododendron in the [http://www.rhs.org.uk/plants/registration_rhododendron.asp International Rhododendron Registry] held by the [[Royal Horticultural Society]]. Most have been bred for their flowers, but a few are of garden interest because of ornamental leaves and some for ornamental bark or stems.
Some species (e.g. ''[[Rhododendron ponticum]]'' in the [[United Kingdom]]) are invasive as introduced plants, spreading in woodland areas replacing the natural understory. R. ponticum is difficult to eradicate, as its roots can make new shoots.
[[Image:Garden with Rhododendrons.JPG|500px|thumb|right|| A garden with tall Rhododendrons in Lynnwood, Washington]]
;Sample species:
*''[[Rhododendron atlanticum]]''
*''[[Rhododendron canadense]]''
*''[[Rhododendron catawbiense]]''
*''[[Rhododendron chapmanii]]''
*''[[Rhododendron ferrugineum]]''
*''[[Rhododendron groenlandicum]]''
*''[[Rhododendron hirsutum]]''
*''[[Rhododendron lochiae]]''
*''[[Rhododendron luteum]]''
*''[[Rhododendron macrophyllum]]''
*''[[Rhododendron maximum]]''
*''[[Rhododendron moulmainense]]''
*''[[Rhododendron occidentale]]''
*''[[Rhododendron ponticum]]''
*''[[Rhododendron schlippenbachii]]''
*''[[Rhododendron spinuliferum]]''
*''[[Rhododendron tomentosum]]''
A sample hybrid:
*[[Rhododendron 'President Roosevelt'|''Rhododendron'' 'President Roosevelt']]
==Toxicology==
<!-- Image with unknown copyright status removed: [[Image:Bee Collecting Pollen From Rhododendron.JPG|500px|thumb|right|| A Bee Collecting Pollen from a Rhododendron Flower]] -->
Some species are poisonous to grazing animals. These Rhododendrons have a [[toxin]] called [[grayanotoxin]] in their [[pollen]] and [[nectar (plant)|nectar]]. People have been known to become ill from eating [[honey]] made by [[bee]]s feeding on rhododendron and azalea flowers. Rhododendron is extremely toxic to horses, with some animals dying within a few hours of ingesting the plant, although most horses tend to avoid it if they have access to good forage.
===Planting and care===
Like other [[Ericaceae|ericaceous]] plants, most rhododendrons prefer acid soils with a pH of roughly 4.5-5.5; some tropical Vireyas and a few other rhododendron species grow as [[epiphyte]]s and require a planting mix similar to [[orchids]]. Rhododendrons have fibrous roots and prefer well-drained soils high in organic material. In areas with poorly-drained or alkaline soils, rhododendrons are often grown in raised beds using mediums such as composted pine bark.<ref>[http://www.rhododendron.org/soil.htm Soil information for planting rhododendrons]</ref> Mulching and careful watering are important, especially before the plant is established.
===Insects and diseases===
{{Main|List of rhododendron diseases}}
There are a number of insects that either target rhododendrons or will opportunistically attack them. Rhododendron borers and various weevils are major pests of rhododendrons, and many caterpillars will attack rhododendrons. Major diseases include ''[[Phytophthora]]'' root rot, stem and twig fungal dieback; [[Ohio State University Extension]] provides [http://www.ag.ohio-state.edu/~ohioline/hyg-fact/3000/3043.html information on maintaining health of rhododendrons]Rhododendrons can easily be suffocated by other plants.
''Rhododendron'' species are used as food plants by the [[larva]]e of some members of the Order [[Lepidoptera]] ([[butterflies]] and [[moths]]) (See [[List of Lepidoptera that feed on rhododendrons]]).
== Gallery ==
<gallery>
Image:Rhododendron decorum ssp diaprepes -1.jpg|''Rhododendron decorum'' subsp. ''diaprepes''
Image:rhododendron2.jpg
Image:Wild Rhododendrons in Kashmir.jpg|Wild Rhododendrons in Kashmir by [[Edward Molyneux]]; painted before 1908
Image:Rhododendron 1 Fcb981.JPG
Image:Wild Rhododendrons in Whitwick Leicestershire 1155.JPG | Flowering Rhododendrons in Whitwick Leicestershire
</gallery>
==Footnotes==
{{reflist}}
==References==
*Cox, P. A. & Kenneth, N. E. ''The Encyclopedia of Rhododendron Species''. 1997. Glendoick Publishing. ISBN 0-9530533-0-X.
*Davidian, H. H. ''The Rhododendron Species''. In four volumes from 1982-1995. Timber Press. ISBN 0-917304-71-3, ISBN 0-88192-109-2, ISBN 0-88192-168-8, ISBN 0-88192-311-7.
==See also==
* [[List of plants poisonous to equines]]
*[[Chinese herbology#50 fundamental herbs|Chinese herbology]] 50 fundamental herbs
==External links==
* [http://en.wikipedia.org/wiki/Rhododendron Wikipedia article]
* [http://www.efloras.org/florataxon.aspx?flora_id=2&taxon_id=128386 Flora of China: ''Rhododendron'']
* [http://www.wfu.edu/~kronka/kakbek/rhododendrons.html Information on rhododendrons at the Ericaceae web pages of Dr. Kron at Wake Forest University.]
* [http://www.vireya.net/ Information on Vireyas]
* [http://www.rhodophiles.com/ Information on Rhododendrons by Marc Colombel, founder of the Société Bretonne du Rhododendron.]
* [http://rhodyman.net/rahome.html Extensive information on rhododendron species: the history of their discovery, botanical details, toxicity, classification, cultural conditions, care for common problems, and suggestions for companion plants by Steve Henning.]
===Rhododendron Societies===
* [http://rhododendron.org/ American Rhododendron Society]
* [http://www.rhs.org.uk/plants/plant_groups/rhododendrons.asp UK Royal Horticultural Society]
* [http://www.rhodygarden.org/ Rhododendron Species Foundation and Botanical Garden]
* [http://honeybee.helsinki.fi/users/avainola/rhodo/club.htm Société Finlandaise du Rhododendron]
* [http://www.eisa.net.au/~mirra/australi.html Australian Rhododendron Society]
* [http://www.rhodo.org/wissen.php?lang=gb German Rhododendron Society]
