Rhododendron

Rhododendron

Overview
Rhododendron is a genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 of over 1 000 species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 of woody plants in the heath family
Ericaceae
The Ericaceae, commonly known as the heath or heather family, is a group of mostly calcifuge flowering plants. The family is large, with roughly 4000 species spread across 126 genera, making it the 14th most speciose family of flowering plants...

, most with showy flowers. It includes the plants known to gardeners as azalea
Azalea
Azaleas are flowering shrubs comprising two of the eight subgenera of the genus Rhododendron, Pentanthera and Tsutsuji . Azaleas bloom in spring, their flowers often lasting several weeks...

s.

Rhododendron is a genus characterized by shrub
Shrub
A shrub or bush is distinguished from a tree by its multiple stems and shorter height, usually under 5–6 m tall. A large number of plants may become either shrubs or trees, depending on the growing conditions they experience...

s and small to (rarely) large tree
Tree
A tree is a perennial woody plant. It is most often defined as a woody plant that has many secondary branches supported clear of the ground on a single main stem or trunk with clear apical dominance. A minimum height specification at maturity is cited by some authors, varying from 3 m to...

s, the smallest species growing to 10–100 cm (3.9–39.4 ) tall, and the largest, R. giganteum, reported to over 30 metres (98.4 ft) tall. The leaves
Leaf
A leaf is an organ of a vascular plant, as defined in botanical terms, and in particular in plant morphology. Foliage is a mass noun that refers to leaves as a feature of plants....

 are spirally arranged; leaf size can range from 1 centimetre to over 50 cm (19.7 in), exceptionally 100 cm (39.4 in) in R.
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Encyclopedia
Rhododendron is a genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 of over 1 000 species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

 of woody plants in the heath family
Ericaceae
The Ericaceae, commonly known as the heath or heather family, is a group of mostly calcifuge flowering plants. The family is large, with roughly 4000 species spread across 126 genera, making it the 14th most speciose family of flowering plants...

, most with showy flowers. It includes the plants known to gardeners as azalea
Azalea
Azaleas are flowering shrubs comprising two of the eight subgenera of the genus Rhododendron, Pentanthera and Tsutsuji . Azaleas bloom in spring, their flowers often lasting several weeks...

s.

Description


Rhododendron is a genus characterized by shrub
Shrub
A shrub or bush is distinguished from a tree by its multiple stems and shorter height, usually under 5–6 m tall. A large number of plants may become either shrubs or trees, depending on the growing conditions they experience...

s and small to (rarely) large tree
Tree
A tree is a perennial woody plant. It is most often defined as a woody plant that has many secondary branches supported clear of the ground on a single main stem or trunk with clear apical dominance. A minimum height specification at maturity is cited by some authors, varying from 3 m to...

s, the smallest species growing to 10–100 cm (3.9–39.4 ) tall, and the largest, R. giganteum, reported to over 30 metres (98.4 ft) tall. The leaves
Leaf
A leaf is an organ of a vascular plant, as defined in botanical terms, and in particular in plant morphology. Foliage is a mass noun that refers to leaves as a feature of plants....

 are spirally arranged; leaf size can range from 1 centimetre to over 50 cm (19.7 in), exceptionally 100 cm (39.4 in) in R. sinogrande. They may be either evergreen
Evergreen
In botany, an evergreen plant is a plant that has leaves in all seasons. This contrasts with deciduous plants, which completely lose their foliage during the winter or dry season.There are many different kinds of evergreen plants, both trees and shrubs...

 or deciduous
Deciduous
Deciduous means "falling off at maturity" or "tending to fall off", and is typically used in reference to trees or shrubs that lose their leaves seasonally, and to the shedding of other plant structures such as petals after flowering or fruit when ripe...

. 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
Epiphyte
An epiphyte is a plant that grows upon another plant non-parasitically or sometimes upon some other object , derives its moisture and nutrients from the air and rain and sometimes from debris accumulating around it, and is found in the temperate zone and in the...

s. Species in this genus may be part of the heath complex in oak-heath forests in eastern North America.

Taxonomy


The species are organized by subgenus, section, subsection and series.

Subgenera


There are four large and four small subgenera:
  • Subgenus Rhododendron
    Rhododendron subgenus Rhododendron
    Rhododendron subgenus Rhododendron is a subgenus of the genus Rhododendron.The subgenus includes three sections:*Rhododendron sect. Pogonathum...

    L.: small leaf or lepidotes (with scales on the underside of their leaves); several hundred species, type: Rhododendron ferrugineum
    Rhododendron ferrugineum
    Rhododendron ferrugineum is an evergreen shrub that grows just above the tree line in the Alps, Pyrenees, Jura and northern Apennines, on acid soils. It may grow up to 1 m tall and produces clusters of pinkish-red, bell-shaped flowers throughout the summer...

    .
    • The tropical rhododendrons (sect. Vireya
      Rhododendron subgenus Vireya
      Rhododendron subg. Vireya is a tropical subgenus of Rhododendron with 310 known species. Vireyas are native to southeastern Asia and range from Thailand to Australia....

      , about 300 species) are usually included as a section in this subgenus, but sometimes split off as a ninth subgenus.
  • Subgenus Hymenanthes
    Rhododendron subgenus Hymenanthes
    Rhododendron subg. Hymenanthes is a subgenus of the genus Rhododendron, with a widespread distribution in the temperate Northern Hemisphere. The species are evergreen shrubs and small to medium-sized trees , with medium-sized to large leaves...

    (Blume) K.Koch: large leaf or elepidotes (without scales on the underside of their leaves); about 140 species, type: Rhododendron degronianum.
  • Subgenus Pentanthera
    Rhododendron subgenus Pentanthera
    Rhododendron subgenus Pentanthera is a subgenus of the genus Rhododendron. The common name azalea is applied to many of the species, and also to species in some other subgenera.The subgenus includes four sections:...

    G.Don: deciduous azaleas; about 25 species, type Rhododendron luteum
    Rhododendron luteum
    Rhododendron luteum, Yellow Azalea or Honeysuckle Azalea is a species of Rhododendron native to southeastern Europe and southwest Asia. In Europe, it occurs from southern Poland and Austria south through the Balkans and east to southern Russia, and in Asia, east to the Caucasus.It is a shrub...

    .
  • Subgenus Tsutsusi: evergreen azaleas, about 110 species; type Rhododendron indicum.
  • Subgenus Azaleastrum Planch.: five species; type Rhododendron ovatum.
  • Subgenus Candidastrum (Sleumer) Philipson & Philipson: one species; Rhododendron albiflorum.
  • Subgenus Mumeazalea: one species, Rhododendron semibarbatum.
  • Subgenus Therorhodion: one species, Rhododendron camtschaticum.

Species



Species include:
  • Rhododendron arboreum
    Rhododendron arboreum
    Rhododendron arboreum is an evergreen shrub or small tree with a showy display of bright red flowers. It is found in Bhutan, China, India, Nepal, Sri Lanka and Thailand. Rhododendron arboreum is also the national flower of Nepal.-Description:Its name means "tending to be woody or growing in a...

    – Tree Rhododendron
  • Rhododendron arborescens – Sweet Azalea
  • Rhododendron atlanticum
    Rhododendron atlanticum
    Rhododendron atlanticum , is a species of Rhododendron native to coastal areas of the eastern United States, from New Jersey south to Georgia....

    – Dwarf Azalea
  • Rhododendron boninense – a rare Japanese azalea
  • Rhododendron calendulaceum
    Rhododendron calendulaceum
    Rhododendron calendulaceum , is a species of Rhododendron native to the Appalachian Mountains in the eastern United States, ranging from southern New York to northern Georgia....

    – Flame Azalea
  • Rhododendron canadense
    Rhododendron canadense
    Rhododendron canadense is a deciduous flowering shrub that is native to northeastern North America. The wild distribution of the rhodora begins at its easternmost extreme in Canada in Labrador and extends into eastern Ontario and the United States, where it has its most famous home in New England...

    – Rhodora
  • Rhododendron catawbiense
    Rhododendron catawbiense
    Rhododendron catawbiense is a species of Rhododendron native to the eastern United States, growing mainly in the Appalachian Mountains from Virginia south to northern Alabama....

    – Catawba Rhododendron
  • Rhododendron chapmanii
    Rhododendron chapmanii
    Rhododendron chapmanii, also known as Chapman's Rhododendron, is an evergreen shrub which is endemic to Florida.-Description:Chapman's Rhododendron is an erect shrub that grows up to 2 metres in height. The bark of new growth is reddish-brown, turning graywith age. The leaves are elliptic and are 3...

    – Chapman's Rhododendron
  • Rhododendron ferrugineum
    Rhododendron ferrugineum
    Rhododendron ferrugineum is an evergreen shrub that grows just above the tree line in the Alps, Pyrenees, Jura and northern Apennines, on acid soils. It may grow up to 1 m tall and produces clusters of pinkish-red, bell-shaped flowers throughout the summer...

    – Alpenrose
  • Rhododendron groenlandicum – Bog Labrador Tea
  • Rhododendron hirsutum
    Rhododendron hirsutum
    Hairy Alpenrose or Rhododendron hirsutum is one of the species of rhododendron native to the mountains of Europe. It occurs in the eastern and central Alps, in the Tatra and the Balkans. It grows on carbonate-rich soils....

    – Hairy Alpenrose
  • Rhododendron lochiae
    Rhododendron lochiae
    Rhododendron lochiae is one of two recognised species of Rhododendron endemic to Australia.-Description:It is a small shrub which has glossy, elliptic leaves...

    – Australian Rhododendron
  • Rhododendron luteum
    Rhododendron luteum
    Rhododendron luteum, Yellow Azalea or Honeysuckle Azalea is a species of Rhododendron native to southeastern Europe and southwest Asia. In Europe, it occurs from southern Poland and Austria south through the Balkans and east to southern Russia, and in Asia, east to the Caucasus.It is a shrub...

    – Yellow or Honeysuckle Azalea
  • Rhododendron macrophyllum
    Rhododendron macrophyllum
    Rhododendron macrophyllum, the Pacific Rhododendron, Coast Rhododendron or Big Leaf Rhododendron, is a broadleaf evergreen rhododendron species native to western North America.-Distribution:...

    – Pacific Coast Rhododendron
  • Rhododendron maximum
    Rhododendron maximum
    Rhododendron maximum — also called great rhododendron, great laurel, rosebay rhododendron, American rhododendron or big rhododendron — is a species of Rhododendron native to eastern North America, from Nova Scotia south to northern Alabama.-Description:R. maximum is an evergreen shrub growing to 4...

    – Great or American Rhododendron
  • Rhododendron moulmainense – Westland's Rhododendron
  • Rhododendron mucronulatum - Korean Rhododendron (Korean Rosebay)
  • Rhododendron nilgiricum
  • Rhododendron occidentale
    Rhododendron occidentale
    Rhododendron occidentale, the Western Azalea, is one of two deciduous Rhododendron species native to western North America . The Western Azalea is known to occur as far north as Bandon, Oregon. It is found as far south as the Palomar Mountain area in southern California...

  • Rhododendron oreotrephes
    Rhododendron oreotrephes
    Rhododendron oreotrephes' is rhododendron species native to Burma and south-west China, collected in Sichuan in 1904 by Dr. Ernest Henry Wilson. It is an upright shrub, growing to 4 meters in height, with oblong, often bluish, leaves up to 6 cm in length. Its flowers are pink to lavender.-...

  • Rhododendron periclymenoides
    Rhododendron periclymenoides
    Rhododendron periclymenoides, is a deciduous shrub native to the eastern United States. Flowers appear before the leaves expand. It ranges from New Hampshire to Georgia and Alabama and are relatively frequent though widely scattered along streams, in deciduous forests and woodlands. The ranges of...

    – Pinxterflower
  • Rhododendron ponticum
    Rhododendron ponticum
    Rhododendron ponticum, called Common Rhododendron or Pontic Rhododendron, is a species of Rhododendron native to southern Europe and southwest Asia.-Description:...

  • Rhododendron schlippenbachii
    Rhododendron schlippenbachii
    Rhododendron schlippenbachii is a species of Rhododendron native to the Korean Peninsula and adjacent regions of Manchuria , Japan, and the Russian Far East...

  • Rhododendron spinuliferum
    Rhododendron spinuliferum
    Rhododendron spinuliferum is a species of Rhododendron native to Yunnan, S Sichuan, and Guizhou China....

  • Rhododendron tomentosum

Hybrids


Rhododendrons are extensively hybridized in cultivation, and natural hybrids often occur in areas where species ranges overlap. There are over 28,000 cultivar
Cultivar
A cultivar'Cultivar has two meanings as explained under Formal definition. When used in reference to a taxon, the word does not apply to an individual plant but to all those plants sharing the unique characteristics that define the cultivar. is a plant or group of plants selected for desirable...

s of Rhododendron in the International Rhododendron Registry held by the Royal Horticultural Society
Royal Horticultural Society
The Royal Horticultural Society was founded in 1804 in London, England as the Horticultural Society of London, and gained its present name in a Royal Charter granted in 1861 by Prince Albert...

. 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.
  • Rhododendron 'President Roosevelt'
    Rhododendron 'President Roosevelt'
    Rhododendron 'President Roosevelt' is a popular cultivar of Rhododendron with striking variegated leaves and trusses of bright red flowers that fade to white in the centre. It is named after the 26th president of the United States, Theodore Roosevelt. Height 150–180 cm.-References:*Salley, Homer...


Reclassification


Recent genetic investigations have caused an ongoing realignment of species and groups within the genus, and also have caused the old genus Ledum
Ledum
Ledum is a genus name formerly widely recognised in the family Ericaceae, including 8 species of evergreen shrubs native to cool temperate and subarctic regions of the Northern Hemisphere and commonly known as Labrador Tea....

to be reclassified within subgenus Rhododendron. Further realignment within the subgenera is currently proposed, including the merging of subgenus Hymenanthes into subgenus Pentanthera.

Distribution



Species of the genus Rhododendron occur throughout moist areas of the Northern Hemisphere
Northern Hemisphere
The Northern Hemisphere is the half of a planet that is north of its equator—the word hemisphere literally means “half sphere”. It is also that half of the celestial sphere north of the celestial equator...

 and into the Southern Hemisphere
Southern Hemisphere
The Southern Hemisphere is the part of Earth that lies south of the equator. The word hemisphere literally means 'half ball' or "half sphere"...

 in southeastern Asia
Asia
Asia is the world's largest and most populous continent, located primarily in the eastern and northern hemispheres. It covers 8.7% of the Earth's total surface area and with approximately 3.879 billion people, it hosts 60% of the world's current human population...

 and northern Australasia
Australasia
Australasia is a region of Oceania comprising Australia, New Zealand, the island of New Guinea, and neighbouring islands in the Pacific Ocean. The term was coined by Charles de Brosses in Histoire des navigations aux terres australes...

. No species are native to South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...

 and Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...

.

The highest species diversity is found in the Himalayas
Himalayas
The Himalaya Range or Himalaya Mountains Sanskrit: Devanagari: हिमालय, literally "abode of snow"), usually called the Himalayas or Himalaya for short, is a mountain range in Asia, separating the Indian subcontinent from the Tibetan Plateau...

 from Uttarakhand
Uttarakhand
Uttarakhand , formerly Uttaranchal, is a state in the northern part of India. It is often referred to as the Land of Gods due to the many holy Hindu temples and cities found throughout the state, some of which are among Hinduism's most spiritual and auspicious places of pilgrimage and worship...

, Nepal
Nepal
Nepal , officially the Federal Democratic Republic of Nepal, is a landlocked sovereign state located in South Asia. It is located in the Himalayas and bordered to the north by the People's Republic of China, and to the south, east, and west by the Republic of India...

 and Sikkim
Sikkim
Sikkim is a landlocked Indian state nestled in the Himalayan mountains...

 to Yunnan
Yunnan
Yunnan is a province of the People's Republic of China, located in the far southwest of the country spanning approximately and with a population of 45.7 million . The capital of the province is Kunming. The province borders Burma, Laos, and Vietnam.Yunnan is situated in a mountainous area, with...

 and Sichuan
Sichuan
' , known formerly in the West by its postal map spellings of Szechwan or Szechuan is a province in Southwest China with its capital in Chengdu...

, with other significant areas of diversity in the mountains of Indo-China, Korea
Korea
Korea ) is an East Asian geographic region that is currently divided into two separate sovereign states — North Korea and South Korea. Located on the Korean Peninsula, Korea is bordered by the People's Republic of China to the northwest, Russia to the northeast, and is separated from Japan to the...

, Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...

 and Taiwan
Taiwan
Taiwan , also known, especially in the past, as Formosa , is the largest island of the same-named island group of East Asia in the western Pacific Ocean and located off the southeastern coast of mainland China. The island forms over 99% of the current territory of the Republic of China following...

.

Tropical rhododendron species range from southeast Asia to northern Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...

, with 55 known species in Borneo
Borneo
Borneo is the third largest island in the world and is located north of Java Island, Indonesia, at the geographic centre of Maritime Southeast Asia....

 and 164 in New Guinea
New Guinea
New Guinea is the world's second largest island, after Greenland, covering a land area of 786,000 km2. Located in the southwest Pacific Ocean, it lies geographically to the east of the Malay Archipelago, with which it is sometimes included as part of a greater Indo-Australian Archipelago...

. Interestingly, the species in New Guinea are native to sub-alpine moist grasslands at around 3000 metres in the Central Highlands. Relatively fewer species occur in North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

 and Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

.

Invasive species


Some species (e.g. Rhododendron ponticum
Rhododendron ponticum
Rhododendron ponticum, called Common Rhododendron or Pontic Rhododendron, is a species of Rhododendron native to southern Europe and southwest Asia.-Description:...

in Ireland
Ireland
Ireland is an island to the northwest of continental Europe. It is the third-largest island in Europe and the twentieth-largest island on Earth...

 and the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

) 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.

Insects and 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.

Rhododendron species are used as food plants by the larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...

e of some members of the Order Lepidoptera
Lepidoptera
Lepidoptera is a large order of insects that includes moths and butterflies . It is one of the most widespread and widely recognizable insect orders in the world, encompassing moths and the three superfamilies of butterflies, skipper butterflies, and moth-butterflies...

 (butterflies and moths
Moths
Moths may refer to:* Gustav Moths , German rower* The Moths!, an English indie rock band* MOTHS, members of the Memorable Order of Tin Hats...

) (See List of Lepidoptera that feed on rhododendrons).

Diseases



Major diseases include Phytophthora
Phytophthora
Phytophthora is a genus of plant-damaging Oomycetes , whose member species are capable of causing enormous economic losses on crops worldwide, as well as environmental damage in natural ecosystems. The genus was first described by Heinrich Anton de Bary in 1875...

root rot, stem and twig fungal dieback; Ohio State University Extension provides information on maintaining health of rhododendrons. Rhododendrons can easily be suffocated by other plants.

Cultivation



Both species and hybrid rhododendrons (including azaleas) are used extensively as ornamental plant
Ornamental plant
Ornamental plants are plants that are grown for decorative purposes in gardens and landscape design projects, as house plants, for cut flowers and specimen display...

s in landscaping
Landscaping
Landscaping refers to any activity that modifies the visible features of an area of land, including:# living elements, such as flora or fauna; or what is commonly referred to as gardening, the art and craft of growing plants with a goal of creating a beautiful environment within the landscape.#...

 in many parts of the world, and many species and cultivars are grown commercially for the nursery
Nursery (horticulture)
A nursery is a place where plants are propagated and grown to usable size. They include retail nurseries which sell to the general public, wholesale nurseries which sell only to businesses such as other nurseries and to commercial gardeners, and private nurseries which supply the needs of...

 trade. Rhododendrons are often valued in landscaping for their structure, size, flowers, and the fact that many of them are evergreen. Azaleas are frequently used around foundations and occasionally as hedges, and many larger-leafed rhododendrons lend themselves well to more informal plantings and woodland gardens, or as specimen plants. In some areas, larger rhododendrons can be pruned to encourage more tree-like form, with some species such as R. arboreum
Rhododendron arboreum
Rhododendron arboreum is an evergreen shrub or small tree with a showy display of bright red flowers. It is found in Bhutan, China, India, Nepal, Sri Lanka and Thailand. Rhododendron arboreum is also the national flower of Nepal.-Description:Its name means "tending to be woody or growing in a...

and R. falconeri eventually growing to 10–15 m or more tall.

Commercial growing


Rhododendrons are grown commercially in many areas for sale, and are occasionally collected in the wild, a practice now rare in most areas. Larger commercial growers often ship long distances; in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 most of them are located on the west coast (Oregon
Oregon
Oregon is a state in the Pacific Northwest region of the United States. It is located on the Pacific coast, with Washington to the north, California to the south, Nevada on the southeast and Idaho to the east. The Columbia and Snake rivers delineate much of Oregon's northern and eastern...

, Washington and California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

). Large-scale commercial growing often selects for different characteristics that hobbyist growers might want, such as resistance to root rot when over-watered, ability to be forced into budding early, ease of rooting or other propagation, and saleability.
In the Indian state of Himachal Pradesh, Rhododendron flowers, have been used for some time to make popular fruit and flower wines. The industry is promoted by the state government with tax benefits, looking to promote this industry as a full fledged sub class of its economy.

Planting and care


Like other ericaceous
Ericaceae
The Ericaceae, commonly known as the heath or heather family, is a group of mostly calcifuge flowering plants. The family is large, with roughly 4000 species spread across 126 genera, making it the 14th most speciose family of flowering plants...

 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
Epiphyte
An epiphyte is a plant that grows upon another plant non-parasitically or sometimes upon some other object , derives its moisture and nutrients from the air and rain and sometimes from debris accumulating around it, and is found in the temperate zone and in the...

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. Mulching and careful watering are important, especially before the plant is established.

A new calcium tolerant stock of Rhododendron (patented as "Inkarho") has been exhibited at the RHS Chelsea Flower Show in London (2011). Individual hybrids of rhododendrons have been grafted onto a root stock on a single rhododendron plant that was found growing in a chalk quarry. The root stock is able to grow in calcium rich soil up to a pH of 7.5.

Medicinal potential


Animal studies and in vitro
In vitro
In vitro refers to studies in experimental biology that are conducted using components of an organism that have been isolated from their usual biological context in order to permit a more detailed or more convenient analysis than can be done with whole organisms. Colloquially, these experiments...

research has identified possible anti-inflammatory and hepatoprotective activities which may be due to the anti-oxidant effects of flavonoid
Flavonoid
Flavonoids , are a class of plant secondary metabolites....

s, saponin
Saponin
Saponins are a class of chemical compounds, one of many secondary metabolites found in natural sources, with saponins found in particular abundance in various plant species...

s and phenolic compounds the plant contains. Xiong et al. have found that the root of the plant is able to reduce the activity of NF-κB.

Toxicology


Some species of rhododendron are poisonous to grazing animals because of a toxin
Toxin
A toxin is a poisonous substance produced within living cells or organisms; man-made substances created by artificial processes are thus excluded...

 called grayanotoxin
Grayanotoxin
Grayanotoxins are a group of closely related toxins found in rhododendrons and other plants of the family Ericaceae. They can be found in honey made from their nectar and cause a very rare poisonous reaction called grayanotoxin poisoning, honey intoxication, or rhododendron poisoning...

 in their pollen
Pollen
Pollen is a fine to coarse powder containing the microgametophytes of seed plants, which produce the male gametes . Pollen grains have a hard coat that protects the sperm cells during the process of their movement from the stamens to the pistil of flowering plants or from the male cone to the...

 and nectar
Nectar (plant)
Nectar is a sugar-rich liquid produced by plants. It is produced in glands called nectaries, either within the flowers, in which it attracts pollinating animals, or by extrafloral nectaries, which provide a nutrient source to animal mutualists, which in turn provide anti-herbivore protection...

. People have been known to become ill from eating honey
Honey
Honey is a sweet food made by bees using nectar from flowers. The variety produced by honey bees is the one most commonly referred to and is the type of honey collected by beekeepers and consumed by humans...

 made by bee
Bee
Bees are flying insects closely related to wasps and ants, and are known for their role in pollination and for producing honey and beeswax. Bees are a monophyletic lineage within the superfamily Apoidea, presently classified by the unranked taxon name Anthophila...

s feeding on rhododendron and azalea flowers. Xenophon
Xenophon
Xenophon , son of Gryllus, of the deme Erchia of Athens, also known as Xenophon of Athens, was a Greek historian, soldier, mercenary, philosopher and a contemporary and admirer of Socrates...

 described the odd behavior of Greek
Greeks
The Greeks, also known as the Hellenes , are a nation and ethnic group native to Greece, Cyprus and neighboring regions. They also form a significant diaspora, with Greek communities established around the world....

 soldiers after having consumed honey in a village surrounded by Rhododendron ponticum during the march of the Ten Thousand
Ten Thousand (Greek)
The Ten Thousand were a group of mercenary units, mainly Greek, drawn up by Cyrus the Younger to attempt to wrest the throne of the Persian Empire from his brother, Artaxerxes II...

 in 401 BC
401 BC
Year 401 BC was a year of the pre-Julian Roman calendar. At the time, it was known as the Year of the Tribunate of Potitus, Cossus, Camillus, Ambustus, Mamercinus and Iullus...

. Pompey
Pompey
Gnaeus Pompeius Magnus, also known as Pompey or Pompey the Great , was a military and political leader of the late Roman Republic...

's soldiers reportedly suffered lethal casualties following the consumption of honey made from Rhododendron deliberately left behind by Pontic
Pontic Greeks
The Pontians are an ethnic group traditionally living in the Pontus region, the shores of Turkey's Black Sea...

 forces in 67 BC
67 BC
Year 67 BC was a year of the pre-Julian Roman calendar. At the time it was known as the Year of the Consulship of Piso and Glabrio...

 during the Third Mithridatic War
Third Mithridatic War
The Third Mithridatic War was the last and longest of three Mithridatic Wars fought between Mithridates VI of Pontus and his allies and the Roman Republic...

. Later, it was recognized that honey resulting from these plants has a slightly hallucinogenic and laxative
Laxative
Laxatives are foods, compounds, or drugs taken to induce bowel movements or to loosen the stool, most often taken to treat constipation. Certain stimulant, lubricant, and saline laxatives are used to evacuate the colon for rectal and/or bowel examinations, and may be supplemented by enemas under...

 effect. The suspect rhododendrons are Rhododendron ponticum
Rhododendron ponticum
Rhododendron ponticum, called Common Rhododendron or Pontic Rhododendron, is a species of Rhododendron native to southern Europe and southwest Asia.-Description:...

and Rhododendron luteum
Rhododendron luteum
Rhododendron luteum, Yellow Azalea or Honeysuckle Azalea is a species of Rhododendron native to southeastern Europe and southwest Asia. In Europe, it occurs from southern Poland and Austria south through the Balkans and east to southern Russia, and in Asia, east to the Caucasus.It is a shrub...

(formerly Azalea pontica), both found in northern Asia Minor
Asia Minor
Asia Minor is a geographical location at the westernmost protrusion of Asia, also called Anatolia, and corresponds to the western two thirds of the Asian part of Turkey...

. Eleven similar cases have been documented in Istanbul
Istanbul
Istanbul , historically known as Byzantium and Constantinople , is the largest city of Turkey. Istanbul metropolitan province had 13.26 million people living in it as of December, 2010, which is 18% of Turkey's population and the 3rd largest metropolitan area in Europe after London and...

, Turkey
Turkey
Turkey , known officially as the Republic of Turkey , is a Eurasian country located in Western Asia and in East Thrace in Southeastern Europe...

 during the 1980s. 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. The effects of Rhododendron ponticum was mentioned in the 2009 film Sherlock Holmes
Sherlock Holmes (2009 film)
Sherlock Holmes is a 2009 action-mystery film based on the character of the same name created by Sir Arthur Conan Doyle. The film was directed by Guy Ritchie and produced by Joel Silver, Lionel Wigram, Susan Downey and Dan Lin. The screenplay by Michael Robert Johnson, Anthony Peckham and Simon...

 as a proposed way to arrange a fake execution.

Symbolism


Rhododendron ponticum
Rhododendron ponticum
Rhododendron ponticum, called Common Rhododendron or Pontic Rhododendron, is a species of Rhododendron native to southern Europe and southwest Asia.-Description:...

is the state flower
Floral emblem
In a number of countries, plants have been chosen as symbols to represent specific geographic areas. Some countries have a country-wide floral emblem; others in addition have symbols representing subdivisions. Different processes have been used to adopt these symbols - some are conferred by...

 of Indian-administered Kashmir
Jammu and Kashmir
Jammu and Kashmir is the northernmost state of India. It is situated mostly in the Himalayan mountains. Jammu and Kashmir shares a border with the states of Himachal Pradesh and Punjab to the south and internationally with the People's Republic of China to the north and east and the...

 and Pakistan Controlled Kashmir
Azad Kashmir
Azad Jammu and Kashmir or Azad Kashmir for short, is the southernmost political entity within the Pakistani-administered part of the former princely state of Jammu and Kashmir...

. Rhododendron arboreum
Rhododendron arboreum
Rhododendron arboreum is an evergreen shrub or small tree with a showy display of bright red flowers. It is found in Bhutan, China, India, Nepal, Sri Lanka and Thailand. Rhododendron arboreum is also the national flower of Nepal.-Description:Its name means "tending to be woody or growing in a...

(Lali Guransh) is the national flower of Nepal
Nepal
Nepal , officially the Federal Democratic Republic of Nepal, is a landlocked sovereign state located in South Asia. It is located in the Himalayas and bordered to the north by the People's Republic of China, and to the south, east, and west by the Republic of India...

. Rhododendron niveum is the state tree of Sikkim
Sikkim
Sikkim is a landlocked Indian state nestled in the Himalayan mountains...

 in India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

. Rhododendron is also the state tree of the state of Uttarakhand
Uttarakhand
Uttarakhand , formerly Uttaranchal, is a state in the northern part of India. It is often referred to as the Land of Gods due to the many holy Hindu temples and cities found throughout the state, some of which are among Hinduism's most spiritual and auspicious places of pilgrimage and worship...

, India.

Rhododendron catawbiense
Rhododendron catawbiense
Rhododendron catawbiense is a species of Rhododendron native to the eastern United States, growing mainly in the Appalachian Mountains from Virginia south to northern Alabama....

, the most widespread rhododendron of the Appalachian Mountains
Appalachian Mountains
The Appalachian Mountains #Whether the stressed vowel is or ,#Whether the "ch" is pronounced as a fricative or an affricate , and#Whether the final vowel is the monophthong or the diphthong .), often called the Appalachians, are a system of mountains in eastern North America. The Appalachians...

, is the state flower of West Virginia
West Virginia
West Virginia is a state in the Appalachian and Southeastern regions of the United States, bordered by Virginia to the southeast, Kentucky to the southwest, Ohio to the northwest, Pennsylvania to the northeast and Maryland to the east...

, and is in the Flag of West Virginia
Flag of West Virginia
The flag of the state of West Virginia consists of the state's coat of arms on a white field with a dark blue border. The coat of arms, primarily consisting of the state seal, is featured in the flag's center. The coat of arms symbolizes the state's principal pursuits and resources...

. Rhododendron macrophyllum
Rhododendron macrophyllum
Rhododendron macrophyllum, the Pacific Rhododendron, Coast Rhododendron or Big Leaf Rhododendron, is a broadleaf evergreen rhododendron species native to western North America.-Distribution:...

, a widespread rhododendron of the Pacific Northwest
Pacific Northwest
The Pacific Northwest is a region in northwestern North America, bounded by the Pacific Ocean to the west and, loosely, by the Rocky Mountains on the east. Definitions of the region vary and there is no commonly agreed upon boundary, even among Pacific Northwesterners. A common concept of the...

, is the state flower of Washington.

Literature


In Joyce's
James Joyce
James Augustine Aloysius Joyce was an Irish novelist and poet, considered to be one of the most influential writers in the modernist avant-garde of the early 20th century...

 Ulysses
Ulysses (novel)
Ulysses is a novel by the Irish author James Joyce. It was first serialised in parts in the American journal The Little Review from March 1918 to December 1920, and then published in its entirety by Sylvia Beach on 2 February 1922, in Paris. One of the most important works of Modernist literature,...

, rhododendrons play an important role in Leopold and Molly's early courtship: Molly remembers them in her soliloquy - "the sun shines for you he said the day we were lying among the rhododendrons on Howth
Howth
Howth is an area in Fingal County near Dublin city in Ireland. Originally just a small fishing village, Howth with its surrounding rural district is now a busy suburb of Dublin, with a mix of dense residential development and wild hillside, all on the peninsula of Howth Head. The only...

 head in the grey tweed suit and his straw hat the day I got him to propose to me". Jasper Fforde
Jasper Fforde
Jasper Fforde is a British novelist. Fforde's first novel, The Eyre Affair, was published in 2001. Fforde is mainly known for his Thursday Next novels, although he has written several books in the loosely connected Nursery Crime series and begun two more independent series: The Last Dragonslayer...

 a british author, also uses rhododendron as a motif throughout many of his published books. See Thursday Next
Thursday Next
Thursday Next is the main protagonist in a series of comic fantasy, alternate history novels by the British author Jasper Fforde. She was first introduced in Fforde's first published novel, The Eyre Affair, released on July 19, 2001 by Hodder & Stoughton. , the series comprises six books, in two...

 series,and Shades of Grey
Shades of Grey 1: The Road to High Saffron
Shades of Grey 1: The Road to High Saffron is a dystopian novel, the first in the "Shades of Grey" series by novelist Jasper Fforde...

.

Culinary


In Nepal, the flower is considered edible and enjoyed for its sour taste. The people pickle the flower which can last for months and also the flower juice is also being marketed. The flower, fresh or dried, are actually added to fish curry believing that it will soften the bones.

External links




Rhododendron societies