Rhododendron
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''Rhododendron'' (; from
Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek Dark ...
''rhódon'' "rose" and ''déndron'' "tree") is a very large
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
of about 1,024
species In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...
of woody plants in the heath family (Ericaceae). They can be either
evergreen In botany, an evergreen is a plant which has Leaf, foliage that remains green and functional through more than one growing season. This also pertains to plants that retain their foliage only in warm climates, and contrasts with deciduous plants, ...
or
deciduous In the fields of horticulture and Botany, the term ''deciduous'' () means "falling off at maturity" and "tending to fall off", in reference to trees and shrubs that seasonally shed leaves, usually in the autumn; to the shedding of petals, af ...
. Most species are native to eastern Asia and the
Himalaya The Himalayas, or Himalaya (; ; ), is a mountain range in Asia, separating the plains of the Indian subcontinent from the Tibetan Plateau. The range has some of the planet's highest peaks, including the very highest, Mount Everest ...
n region, but smaller numbers occur elsewhere in Asia, and in North America, Europe and Australia. It is the
national flower 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 ...
of
Nepal Nepal (; ne, :ne:नेपाल, नेपाल ), formerly the Federal Democratic Republic of Nepal ( ne, सङ्घीय लोकतान्त्रिक गणतन्त्र नेपाल ), is a landlocked country in S ...
, the state flower of
Washington Washington commonly refers to: * Washington (state), United States * Washington, D.C., the capital of the United States ** A metonym for the federal government of the United States ** Washington metropolitan area, the metropolitan area centered on ...
and
West Virginia West Virginia is a U.S. state, state in the Appalachian Mountains, Appalachian, Mid-Atlantic (United States), Mid-Atlantic and Southeastern United States, Southeastern regions of the United States.The United States Census Bureau, Census Burea ...
in the United States, the state flower of
Nagaland Nagaland () is a landlocked state in the northeastern region of India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area, ...
in India, the provincial flower of
Jiangxi Jiangxi (; ; Postal romanization, formerly romanized as Kiangsi or Chianghsi) is a landlocked Provinces of China, province in East China, the east of the China, People's Republic of China. Its major cities include Nanchang and Jiujiang. Spannin ...
in China and the state tree of
Sikkim Sikkim (; ) is a States and union territories of India, state in Northeastern India. It borders the Tibet Autonomous Region of China in the north and northeast, Bhutan in the east, Province No. 1 of Nepal in the west and West Bengal in the sout ...
and
Uttarakhand Uttarakhand ( , or ; , ), also known as Uttaranchal ( ; the official name until 2007), is a state in the northern part of India. It is often referred to as the "Devbhumi" (literally 'Land of the Gods') due to its religious significance and ...
in India. Most species have brightly colored flowers which bloom from late winter through to early summer.
Azalea Azaleas are flowering shrubs in the genus ''Rhododendron'', particularly the former sections '' Tsutsusi'' (evergreen) and '' Pentanthera'' (deciduous). Azaleas bloom in the spring (April and May in the temperate Northern Hemisphere, and Octo ...
s make up two subgenera of ''Rhododendron''. They are distinguished from "true" rhododendrons by having only five
anther The stamen (plural ''stamina'' or ''stamens'') is the pollen-producing reproductive organ of a flower. Collectively the stamens form the androecium., p. 10 Morphology and terminology A stamen typically consists of a stalk called the filame ...
s per flower.


Species


Description

''Rhododendron'' is a genus of
shrub A shrub (often also called a bush) is a small-to-medium-sized perennial woody plant. Unlike herbaceous plants, shrubs have persistent woody stems above the ground. Shrubs can be either deciduous or evergreen. They are distinguished from trees ...
s and small to (rarely) large
tree In botany, a tree is a perennial plant with an elongated Plant stem, stem, or trunk (botany), trunk, usually supporting branches and leaves. In some usages, the definition of a tree may be narrower, including only woody plants with secondar ...
s, the smallest species growing to tall, and the largest, ''R. protistum'' var. ''giganteum'', reported to tall. The
leaves A leaf (plural, : leaves) is any of the principal appendages of a vascular plant plant stem, stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", wh ...
are spirally arranged; leaf size can range from to over , exceptionally in ''R. sinogrande''. They may be either
evergreen In botany, an evergreen is a plant which has Leaf, foliage that remains green and functional through more than one growing season. This also pertains to plants that retain their foliage only in warm climates, and contrasts with deciduous plants, ...
or
deciduous In the fields of horticulture and Botany, the term ''deciduous'' () means "falling off at maturity" and "tending to fall off", in reference to trees and shrubs that seasonally shed leaves, usually in the autumn; to the shedding of petals, af ...
. In some species, the undersides of the leaves are 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 Section, Sectioning or Sectioned may refer to: Arts, entertainment and media * Section (music), a complete, but not independent, musical idea * Section (typography), a subdivision, especially of a chapter, in books and documents ** Section sign ...
'' Vireya'' that often grow as
epiphyte An epiphyte is an organism that grows on the surface of a plant and derives its moisture and nutrients from the air, rain, water (in marine environments) or from debris accumulating around it. The plants on which epiphytes grow are called Phorophy ...
s. Species in this genus may be part of the heath complex in oak-heath forests in eastern North America. They have frequently been divided based on the presence or absence of scales on the abaxial (lower) leaf surface (
lepidote A leaf ( : leaves) is any of the principal appendages of a vascular plant Vascular plants (), also called tracheophytes () or collectively Tracheophyta (), form a large group of embryophyte, land plants ( accepted known species) that ...
or elepidote). These scales, unique to subgenus ''Rhododendron'', are modified hairs consisting of a polygonal scale attached by a stalk. ''Rhododendron'' are characterised by having
inflorescences An inflorescence is a group or cluster of flowers arranged on a Plant stem, stem that is composed of a main branch or a complicated arrangement of branches. Morphology (biology), Morphologically, it is the modified part of the shoot of sperma ...
with scarious (dry) perulae, a
chromosome number Ploidy () is the number of complete sets of chromosomes in a cell (biology), cell, and hence the number of possible alleles for Autosome, autosomal and Pseudoautosomal region, pseudoautosomal genes. Sets of chromosomes refer to the number of mat ...
of x=13,
fruit In botany, a fruit is the seed-bearing structure in flowering plants that is formed from the ovary after flowering. Fruits are the means by which flowering plants (also known as angiosperms) disseminate their seeds. Edible fruits in particul ...
that has a septicidal capsule, an
ovary The ovary is an organ in the female reproductive system that produces an ovum. When released, this travels down the fallopian tube into the uterus, where it may become fertilized by a sperm. There is an ovary () found on each side of the bo ...
that is superior (or nearly so),
stamens The stamen (plural ''stamina'' or ''stamens'') is the pollen-producing reproductive organ of a flower. Collectively the stamens form the androecium., p. 10 Morphology and terminology A stamen typically consists of a stalk called the filame ...
that have no appendages, and agglutinate (clumped)
pollen Pollen is a powdery substance produced by Spermatophyte, seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects ...
.


Taxonomy

''Rhododendron'' is the largest genus in the family
Ericaceae The Ericaceae are a Family (biology), family of flowering plants, commonly known as the heath or heather family, found most commonly in acidic and infertile growing conditions. The family is large, with c.4250 known species spread across 124 ge ...
, with over 1000 species, (though estimates vary from 850 to 1200) and is morphologically diverse. Consequently, the
taxonomy Taxonomy is the practice and science of categorization or classification (general theory), classification. A taxonomy (or taxonomical classification) is a scheme of classification, especially a hierarchical classification, in which things are ...
has been historically complex.


Early history

Although Rhododendrons had been known since the description of '' Rhododendron hirsutum'' by Charles de l'Écluse (Clusius) in the sixteenth century, and were known to classical writers (Magor 1990), and referred to as ''Chamaerhododendron'' (low-growing rose tree), the genus was first formally described by
Linnaeus Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his Nobility#Ennoblement, ennoblement in 1761 as Carl von Linné#Blunt, Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalise ...
in his
Species Plantarum ' (Latin for "The Species of Plants") is a book by Carl Linnaeus, originally published in 1753, which lists every species of plant known at the time, classified into genus, genera. It is the first work to consistently apply binomial nomenclature ...
in 1753. He listed five species under ''Rhododendron'' (''
Rhododendron ferrugineum ''Rhododendron ferrugineum'', the alpenrose, snow-rose, or rusty-leaved alpenrose is an evergreen shrub that grows just above the tree line in the Alps, Pyrenees, Jura mountains, Jura and northern Apennine Mountains, Apennines, on acid soils. It ...
'' (
type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological Type (biology), ...
), '' R. dauricum'', '' R. hirsutum'', ''R. chamaecistus'' (now '' Rhodothamnus chamaecistus'' (L.) Rchb.) and '' R. maximum''). At that time he considered the then known six species of ''
Azalea Azaleas are flowering shrubs in the genus ''Rhododendron'', particularly the former sections '' Tsutsusi'' (evergreen) and '' Pentanthera'' (deciduous). Azaleas bloom in the spring (April and May in the temperate Northern Hemisphere, and Octo ...
'' that he had described earlier in 1735 in his
Systema Naturae ' (originally in Latin language, Latin written ' with the Orthographic ligature, ligature æ) is one of the major works of the Sweden, Swedish botanist, zoologist and physician Carl Linnaeus (1707–1778) and introduced the Linnaean taxonomy. Al ...
as a separate genus. Linnaeus' six species of ''Azalea'' were '' Azalea indica'', '' A. pontica'', '' A. lutea'', '' A. viscosa'', '' A. lapponica'' and ''A. procumbens'' (now '' Kalmia procumbens''), which he distinguished from ''Rhododendron'' by having five
stamens The stamen (plural ''stamina'' or ''stamens'') is the pollen-producing reproductive organ of a flower. Collectively the stamens form the androecium., p. 10 Morphology and terminology A stamen typically consists of a stalk called the filame ...
, as opposed to ten. As new species of what are now considered ''Rhododendron'' were discovered, they were assigned to separate genera if they seemed to differ significantly from the type species. For instance ''Rhodora'' (Linnaeus 1763) for '' Rhododendron canadense'', ''Vireya'' ( Blume 1826) and ''Hymenanthes'' (Blume 1826) for ''Rhododendron metternichii'', now R. degronianum. Meanwhile, other botanists such as
Salisbury Salisbury ( ) is a city status in the United Kingdom, cathedral city in Wiltshire, England with a population of 41,820, at the confluence of the rivers River Avon, Hampshire, Avon, River Nadder, Nadder and River Bourne, Wiltshire, Bourne. The ...
(1796) and Tate (1831) began to question the distinction between ''Azalea'' and ''Rhododendron'', and finally in 1836, ''Azalea'' was incorporated into ''Rhododendron'' and the genus divided into eight sections. Of these ''Tsutsutsi'' ('' Tsutsusi''), '' Pentanthera'', '' Pogonanthum'', '' Ponticum'' and '' Rhodora'' are still used, the other sections being ''Lepipherum'', ''Booram'', and ''Chamaecistus''. This structure largely survived till recently (2004), following which the development of molecular phylogeny led to major re-examinations of traditional morphological classifications, although other authors such as Candolle, who described six sections, used slightly different numeration. Soon, as more species became available in the nineteenth century so did a better understanding of the characteristics necessary for the major divisions. Chief amongst these were Maximovicz's ''Rhododendreae Asiae Orientali'' and Planchon. Maximovicz used flower bud position and its relationship with leaf buds to create eight "Sections".
Bentham and Hooker A list of systems of plant taxonomy, taxonomic system, the Bentham & Hooker system for seed plants, was published in Bentham and Hooker's ''Genera plantarum ad exemplaria imprimis in herbariis kewensibus servata definita'' in three volumes between ...
used a similar scheme, but called the divisions "Series". It was not until 1893 that
Koehne The surname Koehne may refer to: History "Koehne" is the North German language, German variant of the name "Kuehne". People * Bernhard Karl von Koehne (1817–1887), Russian heraldist and numismatist * Bernhard Adalbert Emil Koehne (1848&nda ...
appreciated the significance of scaling and hence the separation of lepidote and elepidote species. The large number of species that were available by the early twentieth century prompted a new approach when Balfour introduced the concept of grouping species into
series Series may refer to: People with the name * Caroline Series Caroline Mary Series (born 24 March 1951) is an English mathematician known for her work in hyperbolic geometry, Kleinian groups and dynamical systems. Early life and education S ...
. ''The Species of Rhododendron'' referred to this series concept as the Balfourian system. That system continued up to modern times in Davidian's four volume ''The Rhododendron Species''.


Modern era

The next major attempt at classification was by Sleumer who from 1934 began incorporating the Balfourian series into the older hierarchical structure of subgenera and sections, according to the
International Code of Botanical Nomenclature The ''International Code of Nomenclature for algae, fungi, and plants'' (ICN) is the set of rules and recommendations dealing with the formal botanical names that are given to plants, fungi and a few other groups of organisms, all those "trad ...
, culminating in 1949 with his "Ein System der Gattung ''Rhododendron'' L.", and subsequent refinements. Most of the Balfourian series are represented by Sleumer as subsections, though some appear as sections or even subgenera. Sleumer based his system on the relationship of the flower buds to the leaf buds, habitat, flower structure, and whether the leaves were lepidote or non-lepidote. While Sleumer's work was widely accepted, many in the United States and the United Kingdom continued to use the simpler Balfourian system of the Edinburgh group. Sleumer's system underwent many revisions by others, predominantly the Edinburgh group in their continuing
Royal Botanic Garden Edinburgh The Royal Botanic Garden Edinburgh (RBGE) is a scientific centre for the study of plants, their diversity and conservation, as well as a popular tourist attraction. Founded in 1670 as a physic garden A physic garden is a type of herb garde ...
notes. Cullen of the Edinburgh group, placing more emphasis on the lepidote characteristics of the leaves, united all of the lepidote species into subgenus ''Rhododendron'', including four of Sleumer's subgenera (''Rhododendron'', ''Pseudoazalea'', ''Pseudorhodorastrum'', ''Rhodorastrum''). In 1986 Philipson & Philipson raised two sections of subgenus ''Aleastrum'' (''Mumeazalea'', ''Candidastrum'') to subgenera, while reducing genus ''Therorhodion'' to a subgenus of ''Rhododendron''. In 1987 Spethmann, adding
phytochemical Phytochemicals are chemical compounds produced by plants, generally to help them resist fungi, bacteria and plant virus infections, and also consumption by insects and other animals. The name comes . Some phytochemicals have been used as poisons ...
features proposed a system with fifteen subgenera grouped into three 'chorus' subgenera. A number of closely related genera had been included together with ''Rhododendron'' in a former tribe, Rhodoreae. These have been progressively incorporated into ''Rhododendron''. Chamberlain and Rae moved the
monotypic In biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of Cell (biology), c ...
section ''Tsusiopsis'' together with the monotypic genus ''Tsusiophyllum'' into section ''Tsutsusi'', while Kron & Judd reduced genus ''
Ledum ''Ledum'' was a genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological ...
'' to a subsection of section ''Rhododendron''. Then Judd & Kron moved two species (''
Rhododendron schlippenbachii ''Rhododendron schlippenbachii'', the royal azalea, is a species of ''Rhododendron ''Rhododendron'' (; from Ancient Greek ''rhódon'' "rose" and ''déndron'' "tree") is a very large genus of about 1,024 species of woody plants in the Eric ...
'', '' R. quinquefolium'') from section ''Brachybachii'', subgenus ''Tsutsusi'' and two from section ''Rhodora'', subgenus ''Pentanthera'' ('' R. albrechtii'', '' R. pentaphyllum'') into section ''Sciadorhodion'', subgenus ''Pentanthera''. Finally Chamberlain brought the various systems together in 1996, with 1,025 species divided into eight subgenera. For a comparison of the Sleumer and Chamberlain schemata see Table 1 of Goetsch (2005).


Phylogenetic analyses

The era of molecular analysis rather than descriptive features can be dated to the work of Kurashige (1988) and Kron (1997) who used matK
sequencing In genetics Genetics is the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) It is an important branch in biology because heredity is vital to organisms' evolution. Gregor Mendel, a Moravian Augustinians ...
. Later Gao ''et al.'' (2002) used ITS sequences to determine a
cladistic Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups (" clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived ...
analysis. They confirmed that the genus ''Rhododendron'' was
monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population Population typically refers to the number of ...
, with subgenus ''Therorhodion'' in the basal position, consistent with the matK studies. Following publication of the studies of Goetsch ''et al.'' (2005) with
RPB2 DNA-directed RNA polymerase II subunit RPB2 is an enzyme that in humans is encoded by the ''POLR2B'' gene. This gene encodes the second largest subunit of RNA polymerase II, the polymerase responsible for synthesizing messenger RNA in eukaryotes. ...
, there began an ongoing realignment of species and groups within the genus, based on evolutionary relationships. Their work was more supportive of Sleumer's original system than the later modifications introduced by Chamberlain ''et al.''. 2005 Annual ARS Convention The major finding of Goetsch and colleagues was that all species examined (except ''R. camtschaticum'', subgenus ''Therorhodion'') formed three major
clades A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic – that is, composed of a common ancestor and all its lineage (evolution), lineal descendants – on a phylogenetic tree. ...
which they labelled A, B and C, with the subgenera ''Rhododendron'' and ''Hymenanthes'' nested within clades A and B as
monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population Population typically refers to the number of ...
groups respectively. By contrast subgenera ''Azaleastrum'' and ''Pentanthera'' were
polyphyletic A polyphyletic group is an assemblage of organisms or other evolving elements that is of mixed evolutionary origin. The term is often applied to groups that share similar features known as Homoplasy, homoplasies, which are explained as a result ...
, while ''R. camtschaticum'' appeared as a
sister A sister is a woman or a girl who shares one or more parents with another individual; a female sibling. The male counterpart is a brother. Although the term typically refers to a family, familial relationship, it is sometimes used endearingly to r ...
to all other rhododendrons. The small polyphyletic subgenera ''Pentanthera'' and ''Azaleastrum'' were divided between two clades. The four sections of ''Pentanthera'' between clades B and C, with two each, while ''Azaleastrum'' had one section in each of A and C. Thus subgenera ''Azaleastrum'' and ''Pentanthera'' needed to be disassembled, and ''Rhododendron'', ''Hymenanthes'' and ''Tsutsusi'' correspondingly expanded. In addition to the two separate genera included under ''Rhododendron'' by Chamberlain (''
Ledum ''Ledum'' was a genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological ...
'', ''Tsusiophyllum''), Goetsch ''et al.''. added ''
Menziesia ''Menziesia'' was a genus of angiosperms, flowering plant in the family Ericaceae. More recently it has been reclassified within the genus ''Rhododendron''. it was formally transferred in 2011. Species * ''Menziesia ciliicalyx'' (Miq.) Maxim. = ...
'' (Clade C). Despite a degree of
paraphyly In taxonomy (general), taxonomy, a group is paraphyletic if it consists of the group's most recent common ancestor, last common ancestor and most of its descendants, excluding a few Monophyly, monophyletic subgroups. The group is said to be pa ...
, the subgenus ''Rhododendron'' was otherwise untouched with regard to its three sections but four other subgenera were eliminated and one new subgenus created, leaving a total of five subgenera in all, from eight in Chamberlain's scheme. The discontinued subgenera are ''Pentanthera'', ''Tsutsusi'', ''Candidastrum'' and ''Mumeazalea'', while a new subgenus was created by elevating subgenus ''Azaleastrum'' section ''Choniastrum'' to subgenus rank. Subgenus ''Pentanthera'' (deciduous azaleas) with its four sections was dismembered by eliminating two sections and redistributing the other two between the existing subgenera in clades B (''Hymenanthes'') and C (''Azaleastrum''), although the name was retained in section ''Pentanthera'' (14 species) which was moved to subgenus ''Hymenanthes''. Of the remaining three sections, monotypic ''Viscidula'' was discontinued by moving '' Rhododendron nipponicum'' to ''Tsutsusi'' (C), while ''Rhodora'' (2 species) was itself polyphyletic and was broken up by moving '' Rhododendron canadense'' to section ''Pentanthera'' (B) and '' Rhododendron vaseyi'' to section ''Sciadorhodion'', which then became a new section of subgenus ''Azaleastrum'' (C). Subgenus ''Tsutsusi'' (C) was reduced to section status retaining the name, and included in subgenus ''Azaleastrum''. Of the three minor subgenera, all in C, two were discontinued. The single species of
monotypic In biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of Cell (biology), c ...
subgenus ''Candidastrum'' ('' Rhododendron albiflorum'') was moved to subgenus ''Azaleastrum'', section ''Sciadorhodion''. Similarly the single species in monotypic subgenus ''Mumeazalea'' ('' Rhododendron semibarbatum'') was placed in the new section ''Tsutsusi'', subgenus ''Azaleastrum''. Genus ''Menziesa'' (9 species) was also added to section ''Sciadorhodion''. The remaining small subgenus ''Therorhodion'' with its two species was left intact. Thus two subgenera, ''Hymenanthes'' and ''Azaleastrum'' were expanded at the expense of four subgenera that were eliminated, although ''Azaleastrum'' lost one section (''Choniastrum'') as a new subgenus, since it was a distinct subclade in A. In all, ''Hymenanthes'' increased from one to two sections, while ''Azaleastrum'', by losing one section and gaining two increased from two to three sections. (See schemata under
Subgenera In biology, a subgenus (plural: subgenera) is a taxonomic rank directly below genus. In the International Code of Zoological Nomenclature, a subgeneric name can be used independently or included in a binomen, species name, in parentheses, placed ...
) (Table 1.) Subsequent research has supported the revision by Goetsch, although has largely concentrated on further defining the phylogeny within the subdivisions. In 2011 the two species of ''Diplarche'' were also added to ''Rhododendron'', ''
incertae sedis ' () or ''problematica'' is a term used for a taxonomy (biology), taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomen ...
''.


Subdivision

This
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
has been progressively subdivided into a hierarchy of
subgenus In biology, a subgenus (plural: subgenera) is a taxonomic rank directly below genus. In the International Code of Zoological Nomenclature, a subgeneric name can be used independently or included in a binomen, species name, in parentheses, placed ...
,
section Section, Sectioning or Sectioned may refer to: Arts, entertainment and media * Section (music), a complete, but not independent, musical idea * Section (typography), a subdivision, especially of a chapter, in books and documents ** Section sign ...
, subsection, and
species In biology, a species is the basic unit of Taxonomy (biology), classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of ...
.


Subgenera

Terminology from the Sleumer (1949) system is frequently found in older literature, with five subgenera and is as follows; * Subgenus ''Lepidorrhodium'' Koehne: Lepidotes. 3 sections * Subgenus ''Eurhododendron'' Maxim.: Elipidotes. * Subgenus ''Pseudanthodendron'' Sleumer: Deciduous azaleas. 3 sections * Subgenus ''Anthodendron'' Rehder & Wilson: Evergreen azaleas. 3 sections * Subgenus ''Azaleastrum'' Planch.: 4 sections In the later traditional classification, attributed to Chamberlain (1996), and as used by horticulturalists and the
American Rhododendron Society The American Rhododendron Society (ARS) is a non-profit organization whose mission is to encourage interest in, and disseminate information about, the genus ''Rhododendron''. Members' experience ranges from novice to expert. The society provides a ...
, ''Rhododendron'' has eight
subgenera In biology, a subgenus (plural: subgenera) is a taxonomic rank directly below genus. In the International Code of Zoological Nomenclature, a subgeneric name can be used independently or included in a binomen, species name, in parentheses, placed ...
based on
morphology Morphology, from the Greek and meaning "study of shape", may refer to: Disciplines * Morphology (archaeology), study of the shapes or forms of artifacts *Morphology (astronomy) Galaxy morphological classification is a system used by astronomers ...
, namely the presence of scales (lepidote), deciduousness of leaves, and the floral and vegetative branching patterns, after Sleumer (1980). These consist of four large and four small subgenera. The first two subgenera (''Rhododendron'' and ''Hymenanthes'') represent the species commonly considered as 'Rhododendrons'. The next two smaller subgenera (''Pentanthera'' and ''Tsutsusi'') represent the 'Azaleas'. The remaining four subgenera contain very few species. The largest of these is subgenus ''Rhododendron'', containing nearly half of all known species and all of the lepidote species. *Subgenus ''
Rhododendron ''Rhododendron'' (; from Ancient Greek ''rhódon'' "rose" and ''déndron'' "tree") is a very large genus of about 1,024 species of woody plants in the Ericaceae, heath family (Ericaceae). They can be either evergreen or deciduous. Most specie ...
'' : Small leaf or lepidotes (scales on the underside of the leaves). 3 sections, 462 species,
type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological Type (biology), ...
: ''
Rhododendron ferrugineum ''Rhododendron ferrugineum'', the alpenrose, snow-rose, or rusty-leaved alpenrose is an evergreen shrub that grows just above the tree line in the Alps, Pyrenees, Jura mountains, Jura and northern Apennine Mountains, Apennines, on acid soils. It ...
''. *Subgenus '' Hymenanthes'' : Large leaf or elepidotes (without scales). 1 section, 224 species, type '' Rhododendron degronianum''. *Subgenus '' Pentanthera'' : Deciduous azaleas. 4 sections, 23 species, type '' Rhododendron luteum''. *Subgenus '' Tsutsusi'' : Evergreen azaleas. 2 sections, 80 species, type '' Rhododendron indicum''. *Subgenus '' Azaleastrum'' : 2 sections, 16 species, type '' Rhododendron ovatum''. *Subgenus ''Candidastrum'' : 1 species, '' Rhododendron albiflorum''. *Subgenus ''Mumeazalea'' : 1 species, '' Rhododendron semibarbatum''. *Subgenus ''Therorhodion'' : 2 species ('' Rhododendron camtschaticum'', '' Rhododendron redowskianun''). For a comparison of the Sleumer and Chamberlain systems, see Goetsch ''et al.'' (2005) Table 1. This division was based on a number of what were thought to be key morphological characteristics. These included the position of the inflorescence buds (terminal or lateral), whether lepidote or elepidote, deciduousness of leaves, and whether new foliage was derived from
axils A leaf (plural, : leaves) is any of the principal appendages of a vascular plant plant stem, stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", wh ...
from previous year's shoots or the lowest scaly leaves (Table 2.). Following the
cladistic analysis Cladistics (; ) is an approach to Taxonomy (biology), biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically ...
of Goetsch ''et al.'' (2005) this scheme was simplified, based on the discovery of three major
clades A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyly, monophyletic – that is, composed of a common ancestor and all its lineage (evolution), lineal descendants – on a phylogenetic tree. ...
(A, B, C) as follows. Clade A * Subgenus ''
Rhododendron ''Rhododendron'' (; from Ancient Greek ''rhódon'' "rose" and ''déndron'' "tree") is a very large genus of about 1,024 species of woody plants in the Ericaceae, heath family (Ericaceae). They can be either evergreen or deciduous. Most specie ...
'' : Small leaf or lepidotes (scales on the underside of the leaves). 3 sections, about 400 species,
type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological Type (biology), ...
: ''
Rhododendron ferrugineum ''Rhododendron ferrugineum'', the alpenrose, snow-rose, or rusty-leaved alpenrose is an evergreen shrub that grows just above the tree line in the Alps, Pyrenees, Jura mountains, Jura and northern Apennine Mountains, Apennines, on acid soils. It ...
''. * Subgenus '' Choniastrum'' : 11 species Clade B * Subgenus '' Hymenanthes'' : Large leaf or elepidotes (without scales), including deciduous azaleas. 2 sections, about 140–225 species, type '' Rhododendron degronianum''. Clade C * Subgenus '' Azaleastrum'' : Evergreen azaleas. 3 sections, about 120 species, type '' Rhododendron ovatum''.
Sister taxon In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and t ...
* Subgenus ''Therorhodion'' : 2 species ('' Rhododendron camtschaticum'', '' Rhododendron redowskianun'').


Sections and subsections

The larger subgenera are further subdivided into sections and subsections Some subgenera contain only a single section, and some sections only a single subsection. Shown here is the traditional classification, with species number after Chamberlain (1996), but this scheme is undergoing constant revision. Revisions by Goetsch ''et al.'' (2005) and by Craven ''et al.'' (2008) shown in (''parenthetical italics''). Older ranks such as Series (groups of species) are no longer used but may be found in the literature, but the American Rhododendron Society still uses a similar device, called Alliances *Subgenus ''Rhododendron'' L. (3 sections, 462 species: increased to five sections in 2008) **(''Discovereya (Sleumer) Argent, raised from Vireya'') **'' Pogonathum'' Aitch. & Hemsl. (13 species; Himalaya and adjacent mountains) **(''Pseudovireya (C.B.Clarke) Argent, raised from Vireya'') **''
Rhododendron ''Rhododendron'' (; from Ancient Greek ''rhódon'' "rose" and ''déndron'' "tree") is a very large genus of about 1,024 species of woody plants in the Ericaceae, heath family (Ericaceae). They can be either evergreen or deciduous. Most specie ...
'' L. (149 species in 25 subsections; temperate to subarctic Northern Hemisphere) **'' Vireya'' (Blume) Copel.f. (300 species in 2 subsections; tropical southeast Asia, Australasia. At one time considered separate subgenus) *Subgenus '' Hymenanthes'' (Blume) K.Koch (1 section, 224 species) (''Increased to two sections'') **''Ponticum'' (24 subsections) **('' Pentanthera'' (2 subsections – new section, moved from subgenus ''Pentanthera'') *Subgenus ''Pentanthera'' (4 sections, 23 species) (''Discontinued'') **'' Pentanthera'' (2 subsections – moved to subgenus ''Hymenanthes'') **'' Rhodora'' (L.) G. Don (2 species; '' Rhododendron canadense'', '' Rhododendron vaseyi'') (''Discontinued, redistributed'') **'' Sciadorhodion'' Rehder & Wilson (4 species) (''Moved to subgenus Azaleastrum'') **'' Viscidula'' Matsum. & Nakai (1 species; '' Rhododendron nipponicum'') (''Discontinued, added to section Tsutsusi, subgenus Azaleastrum'') *Subgenus ''Tsutsusi'' (Sweet) Pojarkova (2 sections, 80 species) (''Discontinued, reduced to section and moved to subgenus Azaleastrum'') **'' Brachycalyx'' Sweet (3 alliances, 15 species) **'' Tsutsusi'' (Sweet) Pojarkova (65 species) *Subgenus ''Azaleastrum'' Planch. (2 sections, 16 species) (''Increased to three sections'') **''Azaleastrum'' Planch. (5 species) **(''Choniastrum'' Franch. (11 species) (''Raised to subgenus'')) **('' Sciadorhodion Rehder & Wilson (4 species) (Moved from subgenus Pentanthera'')) **''(Tsutsusi (Sweet) Pojarkova (reduced from subgenus))'' *Subgenus ''Candidastrum'' Franch. (1 species: '' Rhododendron albiflorum'') (''Discontinued, moved to section Sciadorhodion, subgenus Azaleastrum'') *Subgenus ''Mumeazalea'' (Sleumer) W.R. Philipson & M.N. Philipson (1 species: '' Rhododendron semibarbatum'') (''Discontinued, moved to section Tsutsusi, subgenus Azaleastrum'') *Subgenus ''Therorhodion'' A. Gray (2 species) *(''Subgenus Choniastrum Franch. (11 species)'')


Distribution and habitat

Species of the genus ''Rhododendron'' are widely distributed between latitudes 80°N and 20°S and are native to areas from North America to
Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...
,
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, and
Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa Africa is ...
, and from
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to
Queensland ) , nickname = Sunshine State , image_map = Queensland in Australia.svg , map_caption = Location of Queensland in Australia , subdivision_type = Country , subdivision_name = Australia , established_title = Before federation , established_ ...
,
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and the
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. The centres of diversity are in the
Himalayas The Himalayas, or Himalaya (; ; ), is a mountain range in Asia, separating the plains of the Indian subcontinent from the Tibetan Plateau. The range has some of the planet's highest peaks, including the very highest, Mount Everest. Over list ...
and
Malaysia Malaysia ( ; ) is a country in Southeast Asia. The federation, federal constitutional monarchy consists of States and federal territories of Malaysia, thirteen states and three federal territories, separated by the South China Sea into two r ...
, with the greatest species diversity in the Sino-Himalayan region, Southwest China and northern
Burma Myanmar, ; UK pronunciations: US pronunciations incl. . Note: Wikipedia's IPA conventions require indicating /r/ even in British English although only some British English speakers pronounce r at the end of syllables. As John Wells explai ...
, from India –
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,
Uttarakhand Uttarakhand ( , or ; , ), also known as Uttaranchal ( ; the official name until 2007), is a state in the northern part of India. It is often referred to as the "Devbhumi" (literally 'Land of the Gods') due to its religious significance and ...
,
Sikkim Sikkim (; ) is a States and union territories of India, state in Northeastern India. It borders the Tibet Autonomous Region of China in the north and northeast, Bhutan in the east, Province No. 1 of Nepal in the west and West Bengal in the sout ...
and
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to
Nepal Nepal (; ne, :ne:नेपाल, नेपाल ), formerly the Federal Democratic Republic of Nepal ( ne, सङ्घीय लोकतान्त्रिक गणतन्त्र नेपाल ), is a landlocked country in S ...
, northwestern
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and western
Sichuan Sichuan (; zh, c=, labels=no, ; zh, p=Sìchuān; Postal romanization, alternatively romanized as Szechuan or Szechwan; formerly also referred to as "West China" or "Western China" by Protestantism in Sichuan, Protestant missions) is a Prov ...
and southeastern
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. Other significant areas of diversity are in the mountains of
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,
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and
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. More than 90% of ''Rhododendron'' ''sensu'' Chamberlain belong to the Asian subgenera ''Rhododendron'', ''Hymenanthes'' and section ''Tsutsusi''. Of the first two of these, the species are predominantly found in the area of the Himalayas and Southwest China (Sino-Himalayan Region). The 300
tropical The tropics are the regions of Earth surrounding the Equator. They are defined in latitude by the Tropic of Cancer in the Northern Hemisphere at N and the Tropic of Capricorn in the Southern Hemisphere at S. The tropics are also referred to ...
species within the '' Vireya'' section of subgenus ''Rhododendron'' occupy the
Malay archipelago The Malay Archipelago ( Indonesian/ Malay: , tgl, Kapuluang Malay) is the archipelago An archipelago ( ), sometimes called an island group or island chain, is a chain, cluster, or collection of islands, or sometimes a sea containing ...
from their presumed Southeast Asian origin to Northern Australia, with 55 known species in
Borneo Borneo (; id, Kalimantan) is the List of islands by area, third-largest island in the world and the largest in Asia. At the geographic centre of Maritime Southeast Asia, in relation to major Indonesian islands, it is located north of Java Isl ...
and 164 in
New Guinea New Guinea (; Hiri Motu: ''Niu Gini''; id, Papua, or , historically ) is the List of islands by area, world's second-largest island with an area of . Located in Oceania in the southwestern Pacific Ocean, the island is separated from Mainlan ...
. The species in New Guinea are native to
subalpine Montane ecosystems are found on the slopes of mountains. The alpine climate in these regions strongly affects the ecosystem because temperatures lapse rate, fall as elevation increases, causing the ecosystem to stratify. This stratification is ...
moist
grasslands A grassland is an area where the vegetation is dominated by grasses (Poaceae). However, sedge (Cyperaceae) and rush (Juncaceae) can also be found along with variable proportions of legumes, like clover, and other Herbaceous plant, herbs. Grassl ...
at around 3,000 metres above sea level in the Central Highlands. Subgenera ''Rhododendron'' and ''Hymenanthes'', together with section ''Pentanthera'' of subgenus ''Pentanthera'' are also represented to a lesser degree in the Mountainous areas of North America and
Western Eurasia Eurasia (, ) is the largest continent A continent is any of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven geographical regions are commonly regarded as co ...
. Subgenus ''Tsutsusi'' is found in the maritime regions of
East Asia East Asia is the eastern region of Asia, which is defined in both Geography, geographical and culture, ethno-cultural terms. The modern State (polity), states of East Asia include China, Japan, Mongolia, North Korea, South Korea, and Taiwan. ...
(Japan, Korea, Taiwan,
East China East China () is a geographical and a loosely defined cultural List of regions of China, region that covers the eastern coastal area of China. A concept abolished in 1978, for economical purposes the region was defined from 1949 to 1961 by th ...
), but not in North America or Eurasia. In the United States, native ''Rhododendron'' mostly occur in lowland and montane forests in the
Pacific Northwest The Pacific Northwest (sometimes Cascadia, or simply abbreviated as PNW) is a geographic region in western North America bounded by its coastal waters of the Pacific Ocean to the west and, loosely, by the Rocky Mountains to the east. Though ...
,
California California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...
, the
Northeast The points of the compass are a set of horizontal, Radius, radially arrayed compass directions (or Azimuth#In navigation, azimuths) used in navigation and cartography. A compass rose is primarily composed of four cardinal directions—north, east ...
, and the
Appalachian Mountains The Appalachian Mountains (french: Appalaches), often called the Appalachians, are a mountain range, system of mountains in eastern to northeastern North America. The Appalachians first formed roughly 480 million years ago during the Ordovician ...
.


Ecology


Invasive species

''
Rhododendron ponticum ''Rhododendron ponticum'', called common rhododendron or pontic rhododendron, is a species of ''Rhododendron ''Rhododendron'' (; from Ancient Greek ''rhódon'' "rose" and ''déndron'' "tree") is a very large genus of about 1,024 species o ...
'' has become invasive in
Ireland Ireland ( ; ga, Éire ; Ulster Scots dialect, Ulster-Scots: ) is an island in the Atlantic Ocean, North Atlantic Ocean, in Northwestern Europe, north-western Europe. It is separated from Great Britain to its east by the North Channel (Grea ...
and the
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the European mainland, continental mainland. It comprises England, Scotlan ...
. It is an introduced species, spreading in woodland areas and replacing the natural understory. ''R. ponticum'' is difficult to eradicate, as its roots can make new shoots.


Insects

A number of insects either target rhododendrons or will opportunistically attack them. Rhododendron borers and various
weevil Weevils are beetles belonging to the Taxonomic rank, superfamily Curculionoidea, known for their elongated snouts. They are usually small, less than in length, and Herbivore, herbivorous. Approximately 97,000 species of weevils are known. They b ...
s are major pests of rhododendrons, and many
caterpillar Caterpillars ( ) are the larva, larval stage of members of the order Lepidoptera (the insect order comprising butterfly, butterflies and moths). As with most common names, the application of the word is arbitrary, since the larvae of sawfly ...
s will preferentially devour them. ''Rhododendron'' species are used as food plants by the
larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect developmental biology, development such as insects, amphibians, or cnidarians typically have a larval phase of t ...
e (
caterpillars Caterpillars ( ) are the larval stage of members of the order Lepidoptera Lepidoptera ( ) is an order (biology), order of insects that includes butterfly, butterflies and moths (both are called lepidopterans). About 180,000 species of ...
) of some
butterflies Butterflies are insects in the macrolepidopteran clade Rhopalocera from the Order (biology), order Lepidoptera, which also includes moths. Adult butterflies have large, often brightly coloured wings, and conspicuous, fluttering flight. The ...
and
moths Moths are a Paraphyly, paraphyletic group of insects that includes all members of the order Lepidoptera that are not Butterfly, butterflies, with moths making up the vast majority of the order. There are thought to be approximately 160,000 spec ...
; see List of Lepidoptera that feed on rhododendrons.


Diseases

Major diseases include ''
Phytophthora ''Phytophthora'' (from Greek (''phytón''), "plant" and (), "destruction"; "the plant-destroyer") is a genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as ...
'' root rot, stem and twig fungal dieback. Rhododendron bud blast, a fungal condition that causes buds to turn brown and dry before they can open, is caused by the fungus ''Pycnostysanus azaleae'', which may be brought to the plant by the rhododendron leafhopper, ''Graphocephala fennahi''.


Cultivation

Both species and hybrid rhododendrons (including azaleas) are used extensively as
ornamental plant Ornamental plants or garden plants are plants that are primarily grown for their beauty but also for qualities such as scent or how they shape physical space. Many flowering plants and garden varieties tend to be specially bred cultivars that i ...
s in
landscaping Landscaping refers to any activity that modifies the visible features of an area of land, including the following: # organism, Living elements, such as flora or fauna; or what is commonly called gardening, the art and craft of growing plants with ...
in many parts of the world, including both
temperate In geography, the temperate climates of Earth occur in the middle latitudes (23.5° to 66.5° N/S of Equator), which span between the tropics and the polar regions of Earth. These zones generally have wider temperature ranges throughout t ...
and subtemperate regions. Many species and cultivars are grown commercially for the nursery trade. Rhododendrons can be propagated by air layering or stem cuttings. They can self-propagate by sending up shoots from the roots. Sometimes an attached branch that has drooped to the ground will root in damp mulch, and the resulting rooted plant then can be cut off the parent rhododendron. 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 garden A woodland garden is a garden or section of a garden that includes large trees and is laid out so as to appear as more or less natural woodland, though it is often actually an artificial creation. Typically it includes plantings of flowering shrub ...
s, or as specimen plants. In some areas, larger rhododendrons can be pruned to encourage more tree-like form, with some species such as ''
Rhododendron arboreum ''Rhododendron arboreum'', the tree rhododendron, is an evergreen In botany, an evergreen is a plant which has Leaf, foliage that remains green and functional through more than one growing season. This also pertains to plants that retain their ...
'' and '' R. falconeri'' eventually growing to a height of or more.


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, most of them are on the west coast (Oregon, Washington state and California). Large-scale commercial growing often selects for different characteristics than hobbyist growers might want, such as resistance to root rot when overwatered, ability to be forced into budding early, ease of rooting or other propagation, and saleability.


Horticultural divisions

Horticulturally, rhododendrons may be divided into the following groups: * Evergreen rhododendrons - large group of evergreen shrubs that vary greatly in size. Most rhododendron flowers are bell-shaped and have 10 stamens. * Vireya (
Malesia Malesia is a biogeographical region straddling the Equator and the boundaries of the Indomalayan and Australasian realms, and also a phytogeographical floristic region in the Paleotropical Kingdom. It has been given different definitions ...
n) rhododendrons:
epiphytic An epiphyte is an organism that grows on the surface of a plant and derives its moisture and nutrients from the air, rain, water (in marine environments) or from debris accumulating around it. The plants on which epiphytes grow are called Phorophy ...
tender shrubs * Azaleas – group of shrubs which have smaller and thinner leaves than evergreen rhododendrons. They are generally medium-sized shrubs with smaller funnel-shaped flowers that usually have 5 stamens: ** Deciduous hybrid azaleas: *** Exbury hybrids – derived from the Knap Hill hybrids, developed by
Lionel de Rothschild Baron Lionel Nathan de Rothschild (22 November 1808 – 3 June 1879) was a British Jewish banker, politician and philanthropist who was a member of the prominent Rothschild banking family of England. He became the first practising Jew to sit a ...
at the Exbury Estate in England. *** Ghent (Gandavense) hybrids – Belgian raised *** Knap Hill hybrids – developed by Anthony Waterer at the
Knap Hill Knap is a surname, and may refer to: * Josef Knap (1900–1973), Czech writer, poet and literary critic * Ted Knap (21st century), American journalist * Tony Knap (1914–2011), college football head coach at Utah State, Boise Stat ...
Nursery in England. *** Mollis hybrids – Dutch and Belgian raised *** New Zealand Ilam hybrids – derived from Knap Hill/Exbury hybrids *** Occidentale hybrids – English raised *** Rustica Flore Pleno hybrids – sweet-scented, double-flowered ** Evergreen hybrid azaleas: *** Gable hybrids – raised by Joseph B. Gable in
Pennsylvania Pennsylvania (; (Pennsylvania Dutch language, Pennsylvania Dutch: )), officially the Commonwealth of Pennsylvania, is a U.S. state, state spanning the Mid-Atlantic (United States), Mid-Atlantic, Northeastern United States, Northeastern, Appa ...
. *** Glenn Dale hybrids – US raised complex hybrids *** Indian (Indica) hybrids – mostly of Belgian origin *** Kaempferi hybrids – Dutch raised *** Kurume hybrids – Japanese raised *** Kyushu hybrids – very hardy Japanese azaleas (to −30 °C) *** Oldhamii hybrids – dwarf hybrids raised at Exbury, England *** Satsuki hybrids – Japanese raised, originally for
bonsai Bonsai ( ja, 盆栽, , tray planting, ) is the Japanese art of growing and training miniature trees in pots, developed from the traditional Chinese art form of ''penjing''. Unlike ''penjing'', which utilizes traditional techniques to produce ...
*** Shammarello hybrids – raised in northern
Ohio Ohio () is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. Of the List of states and territories of the United States, fifty U.S. states, it is the List of U.S. states and territories by area, 34th-l ...
*** Vuyk (Vuykiana) hybrids – raised in the Netherlands * Azaleodendrons – semi-evergreen hybrids between deciduous azaleas and rhododendrons


Planting and care

Like other 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 An epiphyte is an organism that grows on the surface of a plant and derives its moisture and nutrients from the air, rain, water (in marine environments) or from debris accumulating around it. The plants on which epiphytes grow are called Phorophy ...
s and require a planting mix similar to
orchids Orchids are plants that belong to the Family (biology), family Orchidaceae (), a diverse and widespread group of flowering plants with blooms that are often colourful and fragrant. Along with the Asteraceae, they are one of the two largest fam ...
. 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 media such as composted pine bark. Mulching and careful watering are important, especially before the plant is established. A new calcium-tolerant stock of rhododendrons (trademarked as 'Inkarho') has been exhibited at the RHS
Chelsea Flower Show The RHS Chelsea Flower Show, formally known as the ''Great Spring Show'',Phil Clayton, ''The Great Temple Show'' in ''The Garden'' 2008, p.452, The Royal Horticultural Society is a garden A garden is a planned space, usually outdoors, set as ...
in London (2011). Individual hybrids of rhododendrons have been
grafted Grafting or graftage is a horticultural Horticulture is the branch of agriculture that deals with the art, science, technology, and business of plant cultivation. It includes the cultivation of fruits, vegetables, nuts, seeds, herbs, sprou ...
on to a
rootstock A rootstock is part of a plant, often an underground part, from which new above-ground growth can be produced. It could also be described as a stem with a well developed root system, to which a bud from another plant is grafted. It can refer to a ...
on a single rhododendron plant that was found growing in a chalk quarry. The rootstock is able to grow in calcium-rich soil up to a pH of 7.5.


Hybrids

Rhododendrons are extensively hybridized in cultivation, and natural hybrids often occur in areas where species ranges overlap. There are over 28,000
cultivar A cultivar is a type of Horticulture, cultivated plant that people have selected for desired phenotypic trait, traits and when Plant propagation, propagated retain those traits. Methods used to propagate cultivars include: division, root and st ...
s of Rhododendron in th
International Rhododendron Registry
held by the
Royal Horticultural Society The Royal Horticultural Society (RHS), founded in 1804 as the Horticultural Society of London, is the UK's leading gardening charity. The RHS promotes horticulture through its five gardens at RHS Garden Wisley, Wisley (Surrey), RHS Garden Hyde H ...
. 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 hybrids have fragrant flowers—such as the Loderi hybrids, created by crossing '' Rhododendron fortunei'' and '' R. griffithianum''. Other examples include the PJM hybrids, formed from a cross between '' Rhododendron carolinianum'' and '' R. dauricum'', and named after Peter J. Mezitt of Weston Nurseries, Massachusetts.


Uses


Pharmacology

''Rhododendron'' species have long been used in traditional medicine. Animal studies and ''
in vitro ''In vitro'' (meaning in glass, or ''in the glass'') Research, studies are performed with microorganisms, Cell (biology), cells, or biological molecules outside their normal biological context. Colloquially called "test-tube experiments", thes ...
'' research have identified possible anti-inflammatory and hepatoprotective activities which may be due to the antioxidant effects of
flavonoid Flavonoids (or bioflavonoids; from the Latin word ''flavus'', meaning yellow, their color in nature) are a class of polyphenolic secondary metabolites found in plants, and thus commonly consumed in the diets of humans. Chemically, flavonoids ...
s or other
phenolic compound In organic chemistry Organic chemistry is a subdiscipline within chemistry involving the science, scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that co ...
s and
saponin Saponins (Latin "sapon", soap + "-in", one of), also selectively referred to as triterpene glycosides, are bitter-tasting usually toxic plant-derived organic chemicals that have a foamy quality when agitated in water. They are widely distributed ...
s the plant contains. Xiong ''et al.'' have found that the root of the plant is able to reduce the activity of
NF-κB Nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) is a protein complex that controls transcription (genetics), transcription of DNA, cytokine production and cell survival. NF-κB is found in almost all animal cell types and ...
in rats.


Toxicology

Some species of rhododendron are poisonous to grazing animals because of a
toxin A toxin is a naturally occurring organic poison produced by metabolic activities of living cells or organisms. Toxins occur especially as a protein or conjugated protein. The term toxin was first used by organic chemist Ludwig Brieger (1 ...
called
grayanotoxin Grayanotoxins are a group of closely related neurotoxin Neurotoxins are toxins that are destructive to nervous tissue, nerve tissue (causing neurotoxicity). Neurotoxins are an extensive class of exogenous chemical neurological insult (medical) ...
in their
pollen Pollen is a powdery substance produced by Spermatophyte, seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects ...
and
nectar Nectar is a sugar-rich liquid produced by plants in glands called nectaries or nectarines, either within the flowers with which it attracts pollination, pollinating animals, or by extrafloral nectaries, which provide a nutrient source to anim ...
. People have been known to become ill from eating
honey Honey is a sweet and Viscosity, viscous substance made by several Bee, bees, the best-known of which are honey bees. Honey is made and stored to nourish bee colonies. Bees produce honey by gathering and then refining the sugary secretions of ...
made by
bee Bees are winged insects closely related to wasp A wasp is any insect of the narrow-waisted suborder Apocrita of the order Hymenoptera which is neither a bee nor an ant; this excludes the broad-waisted sawflies (Symphyta), which lo ...
s feeding on rhododendron and
azalea Azaleas are flowering shrubs in the genus ''Rhododendron'', particularly the former sections '' Tsutsusi'' (evergreen) and '' Pentanthera'' (deciduous). Azaleas bloom in the spring (April and May in the temperate Northern Hemisphere, and Octo ...
flowers.
Xenophon Xenophon of Athens (; grc, wikt:Ξενοφῶν, Ξενοφῶν ; – probably 355 or 354 BC) was a Greek military leader, philosopher, and historian, born in Athens. At the age of 30, Xenophon was elected commander of one of the biggest Anci ...
described the odd behaviour of
Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...
soldiers after having consumed honey in a village surrounded by ''
Rhododendron ponticum ''Rhododendron ponticum'', called common rhododendron or pontic rhododendron, is a species of ''Rhododendron ''Rhododendron'' (; from Ancient Greek ''rhódon'' "rose" and ''déndron'' "tree") is a very large genus of about 1,024 species o ...
'' during the march of the
Ten Thousand The Ten Thousand ( grc, οἱ Μύριοι, ''oi Myrioi'') were a force of mercenary units, mainly Ancient Greece, Greeks, employed by Cyrus the Younger to attempt to wrest the throne of the Achaemenid Empire, Persian Empire from his brother, Ar ...
in 401 BCE.
Pompey Gnaeus Pompeius Magnus (; 29 September 106 BC – 28 September 48 BC), known in English as Pompey or Pompey the Great, was a leading Roman Republic, Roman general and statesman. He played a significant role in the tr ...
's soldiers reportedly suffered lethal casualties following the consumption of honey made from ''Rhododendron'' deliberately left behind by Pontic forces in 67 BCE during the
Third Mithridatic War The Third Mithridatic War (73–63 BC), the last and longest of the three Mithridatic Wars, was fought between Mithridates VI of Pontus and the Roman Republic. Both sides were joined by a great number of allies dragging the entire east of the ...
. Later, it was recognized that honey resulting from these plants has a slightly
hallucinogenic Hallucinogens are a large, diverse class of psychoactive drugs that can produce altered states of consciousness characterized by major alterations in thought, Mood (psychology), mood, and perception as well as other changes. Most hallucinogens ...
and
laxative Laxatives, purgatives, or aperients are substances that loosen stools and increase bowel movements. They are used to treat and prevent constipation. Laxatives vary as to how they work and the side effects they may have. Certain stimulant, l ...
effect. The suspect rhododendrons are ''
Rhododendron ponticum ''Rhododendron ponticum'', called common rhododendron or pontic rhododendron, is a species of ''Rhododendron ''Rhododendron'' (; from Ancient Greek ''rhódon'' "rose" and ''déndron'' "tree") is a very large genus of about 1,024 species o ...
'' and '' Rhododendron luteum'' (formerly ''Azalea pontica''), both found in northern
Asia Minor Anatolia (also Asia Minor), is a large peninsula in Western Asia and is the western-most extension of continental Asia. The land mass of Anatolia constitutes most of the territory of contemporary Turkey. Geographically, the Anatolian region i ...
. Eleven similar cases during the 1980s have been documented in
Istanbul Istanbul ( , ; tr, İstanbul ), formerly known as Constantinople ( grc-gre, Κωνσταντινούπολις; la, Constantinopolis), is the List of largest cities and towns in Turkey, largest city in Turkey, serving as the country's economic, ...
,
Turkey Turkey ( tr, Türkiye ), officially the Republic of Türkiye ( tr, Türkiye Cumhuriyeti, links=no ), is a transcontinental country located mainly on the Anatolia, Anatolian Peninsula in Western Asia, with a East Thrace, small portion on th ...
. 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 ''R. ponticum'' were mentioned in the 2009 film ''
Sherlock Holmes Sherlock Holmes () is a fictional detective created by British author Arthur Conan Doyle. Referring to himself as a "Private investigator, consulting detective" in the stories, Holmes is known for his proficiency with observation, deduction, f ...
'' as a proposed way to arrange a fake execution. It was also mentioned in the third episode of Season 2 of BBC's '' Sherlock'', speculated to have been a part of Sherlock's fake death scheme.


Culture


Symbolism

In the
language of flowers Floriography (language of flowers) is a means of Cryptography, cryptological communication through the use or arrangement of flowers. Meaning has been attributed to flowers for thousands of years, and some form of floriography has been practiced ...
, the Rhododendron symbolizes danger and to beware. ''
Rhododendron arboreum ''Rhododendron arboreum'', the tree rhododendron, is an evergreen In botany, an evergreen is a plant which has Leaf, foliage that remains green and functional through more than one growing season. This also pertains to plants that retain their ...
'' (''lali guransh'') is the national flower of
Nepal Nepal (; ne, :ne:नेपाल, नेपाल ), formerly the Federal Democratic Republic of Nepal ( ne, सङ्घीय लोकतान्त्रिक गणतन्त्र नेपाल ), is a landlocked country in S ...
. ''R. ponticum'' is the state flower of
Indian-administered Kashmir Kashmir () is the northernmost geographical region of the Indian subcontinent. Until the mid-19th century, the term "Kashmir" denoted only the Kashmir Valley between the Great Himalayas and the Pir Panjal Range. Today, the term encompass ...
and Pakistan-controlled Kashmir. '' Rhododendron niveum'' is the state tree of
Sikkim Sikkim (; ) is a States and union territories of India, state in Northeastern India. It borders the Tibet Autonomous Region of China in the north and northeast, Bhutan in the east, Province No. 1 of Nepal in the west and West Bengal in the sout ...
in
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area, the List of countries and dependencies by population, second-most populous ...
. Rhododendron arboreum is also the state tree of the state of
Uttarakhand Uttarakhand ( , or ; , ), also known as Uttaranchal ( ; the official name until 2007), is a state in the northern part of India. It is often referred to as the "Devbhumi" (literally 'Land of the Gods') due to its religious significance and ...
, India. Pink Rhododendron ('' Rhododendron campanulatum'') is the state flower of
Himachal Pradesh Himachal Pradesh (; ; "Snow-laden Mountain Province") is a state in the northern part of India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, sevent ...
, India. Rhododendron is also the provincial flower of Jiangxi, China and the state flower of
Nagaland Nagaland () is a landlocked state in the northeastern region of India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area, ...
, the 16th state of the Indian Union. ''
Rhododendron maximum ''Rhododendron maximum'' — its common names include great laurel, great rhododendron, rosebay rhododendron, American rhododendron and big rhododendron — is a species of ''Rhododendron'' native to the Appalachians of eastern North America, fro ...
'', the most widespread rhododendron of the
Appalachian Mountains The Appalachian Mountains (french: Appalaches), often called the Appalachians, are a mountain range, system of mountains in eastern to northeastern North America. The Appalachians first formed roughly 480 million years ago during the Ordovician ...
, is the state flower of the US state of
West Virginia West Virginia is a U.S. state, state in the Appalachian Mountains, Appalachian, Mid-Atlantic (United States), Mid-Atlantic and Southeastern United States, Southeastern regions of the United States.The United States Census Bureau, Census Burea ...
, and is in the Flag of West Virginia. ''
Rhododendron macrophyllum ''Rhododendron macrophyllum'', the Pacific rhododendron, California rosebay, California rhododendron, coast rhododendron or big leaf rhododendron, is a large-leaved species of ''Rhododendron'' native to the West Coast of the United States, Pacific ...
'', a widespread rhododendron of the
Pacific Northwest The Pacific Northwest (sometimes Cascadia, or simply abbreviated as PNW) is a geographic region in western North America bounded by its coastal waters of the Pacific Ocean to the west and, loosely, by the Rocky Mountains to the east. Though ...
, is the state flower of the US state of
Washington Washington commonly refers to: * Washington (state), United States * Washington, D.C., the capital of the United States ** A metonym for the federal government of the United States ** Washington metropolitan area, the metropolitan area centered on ...
.


Literature

The nineteenth-century American poet and essayist Ralph Waldo Emerson in 1834 wrote a poem titled "The Rhodora, On Being Asked, Whence Is the Flower", In Joyce's '' Ulysses'', 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 ( ; ; non, Hǫfuð) is an affluent peninsular village and outer suburb of Dublin, Republic of Ireland, Ireland. The district as a whole occupies the greater part of the peninsula of Howth Head, which forms the northern boundary of Dubl ...
head in the grey tweed suit and his straw hat the day I got him to propose to me".
Jasper Fforde Jasper Fforde (born 11 January 1961) is an English novelist, whose first novel, '' The Eyre Affair'', was published in 2001. He is known mainly for his '' Thursday Next'' novels, but has published two books in the loosely connected '' Nursery Cr ...
a British author, also uses rhododendron as a motif throughout many of his published books. See '' Thursday Next'' series, and '' Shades of Grey''. Amongst the
Zomi The Zomi are an ethnic group which can be found in India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area, the List of ...
tribes in
India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area, the List of countries and dependencies by population, second-most populous ...
and
Myanmar Myanmar, ; UK pronunciations: US pronunciations incl. . Note: Wikipedia's IPA conventions require indicating /r/ even in British English although only some British English speakers pronounce r at the end of syllables. As John C. Wells, Joh ...
, "Rhododendrons" called "Ngeisok" is used in a poetic manner to signify a lady. In
Daphne Du Maurier Dame Daphne du Maurier, Lady Browning, (; 13 May 1907 – 19 April 1989) was an English novelist, biographer and playwright. Her parents were actor-manager Gerald du Maurier, Sir Gerald du Maurier and his wife, actress Muriel Beaumont. Her gra ...
's novel ''
Rebecca Rebecca, ; Aramaic, Syriac: , ) from the Hebrew (lit., 'connection'), from Semitic root , 'to tie, couple or join', 'to secure', or 'to snare') () appears in the Hebrew Bible as the wife of Isaac and the mother of Jacob and Esau. According to ...
'', the character of Rebecca is associated with "blood red" rhododendrons throughout the novel, perhaps due to the toxic roots of the plant mirroring the poisonous character of Rebecca. On the other hand, azaleas (a type of rhododendron) represent the second Mrs. De Winter. In the
young adult A young adult is generally a person in the years following adolescence. Definitions and opinions on what qualifies as a young adult vary, with works such as Erik Erikson's Erikson's stages of psychosocial development, stages of human development ...
novel '' Walk Two Moons'' by
Sharon Creech Sharon Creech (born July 29, 1945) is an American writer of children's novels. She was the first American winner of the Carnegie Medal (literary award), Carnegie Medal for British children's books and the first person to win both the American ...
, the protagonist, Sal, and her friend, Phoebe, construct an elaborate story in which they suspect Phoebe's neighbor of murdering her husband and burying his body beneath a rhododendron in her yard. Chapter 14 of the book is entitled "The Rhododendron".


Culinary

The rhododendron is the national flower of
Nepal Nepal (; ne, :ne:नेपाल, नेपाल ), formerly the Federal Democratic Republic of Nepal ( ne, सङ्घीय लोकतान्त्रिक गणतन्त्र नेपाल ), is a landlocked country in S ...
, where the flower is considered edible and enjoyed for its sour taste. The pickled flower can last for months and the flower juice is also marketed. The flower, fresh or dried, is added to fish curry in the belief that it will soften the bones. The juice of rhododendron flower is used to make a
squash Squash may refer to: Sports * Squash (sport), the high-speed racquet sport also known as squash racquets * Squash (professional wrestling), an extremely one-sided match in professional wrestling * Squash tennis, a game similar to squash but pla ...
called burans (named after the flower) in the hilly regions of
Uttarakhand Uttarakhand ( , or ; , ), also known as Uttaranchal ( ; the official name until 2007), is a state in the northern part of India. It is often referred to as the "Devbhumi" (literally 'Land of the Gods') due to its religious significance and ...
. It is admired for its distinctive flavor and color.


Labrador tea

The
herbal tea Herbal teas, also known as herbal infusions and less commonly called tisanes (UK and US , US also ), are beverages made from the infusion or decoction of herbs, spices, or other plant material in hot water. Oftentimes herb tea, or the plain term ...
called Labrador tea (not a true
tea Tea is an aromatic beverage prepared by pouring hot or boiling water over Curing (vegetable preservation), cured or fresh leaves of ''Camellia sinensis'', an evergreen shrub native to East Asia which probably originated in the borderlands of ...
) is made from one of three closely related species: * ''
Rhododendron tomentosum ''Rhododendron tomentosum'' ( syn. ''Ledum palustre''), commonly known as marsh Labrador tea, northern Labrador tea or wild rosemary, is a flowering plant Flowering plants are plants that bear flowers and fruits, and form the clade Angiosper ...
'' (Northern Labrador tea, previously ''
Ledum palustre ''Rhododendron tomentosum'' (synonym (taxonomy), syn. ''Ledum palustre''), commonly known as marsh Labrador tea, northern Labrador tea or wild rosemary, is a flowering plant in the subsection ''Ledum'' of the large genus ''Rhododendron'' in the f ...
'') * ''
Rhododendron groenlandicum ''Rhododendron groenlandicum'' (bog Labrador tea, muskeg tea, swamp tea, or in northern Canada, Hudson's Bay tea; formerly ''Ledum groenlandicum'' or ''Ledum latifolium'') is a flowering A flower, sometimes known as a bloom or blossom In ...
'', (Bog Labrador tea, previously ''
Ledum groenlandicum ''Rhododendron groenlandicum'' (bog Labrador tea, muskeg tea, swamp tea, or in northern Canada, Hudson's Bay tea; formerly ''Ledum groenlandicum'' or ''Ledum latifolium'') is a flowering plant, flowering shrub with white flowers and evergreen lea ...
'' or '' Ledum latifolium'') * ''
Rhododendron neoglandulosum ''Rhododendron columbianum'', commonly known as western Labrador tea, swamp tea, or muskeg tea, is a shrub that is widespread in the western United States and in western Canada, reported from British Columbia, Alberta, Washington (state), Washing ...
'', (Western Labrador tea, or trapper's tea, previously '' Ledum glandulosum'')


Conservation

In the UK the forerunner of the Rhododendron, Camellia and Magnolia Group (RCMG), The Rhododendron Society was founded in 1916. while in Scotland species are being conserved by the Rhododendron Species Conservation Group.


See also

*
List of Award of Garden Merit rhododendrons The following is a list of rhododendron cultivars and species which have gained the Royal Horticultural Society's Award of Garden Merit. They are mostly Hardiness (plants), hardy evergreen shrubs with abundant, brilliantly-coloured, trumpet-shaped ...
* List of Rhododendron diseases *
List of Rhododendron species This List of ''Rhododendron'' species includes species of the genus ''Rhododendron'', which is in the plant family Ericaceae. Depending on the source, there are anywhere from 800 to over 1,100 wild species. The vast majority of ''Rhododendron'' sp ...
* List of Sections in Subgenus Rhododendron


References


Bibliography


Books and book chapters

* (also available online a
Gallica
* * * * In four volumes: Vol. I. ''Lepidotes'' , Vol. II. ''Elepidotes. Arboreum-Lacteum'' , Vol. III. ''Elepidotes Continued, Neriiflorum-Thomsonii, Azaleastrum and Camtschaticum'' , Vol. IV. ''Azaleas'' . * . * *


Articles

* * *


Subdivisions


Azaleas

* *


Tsutsusi

* * * * *


Vireya

* . A reprint from Flora Malesiana ser. I, vol. 6, part 4. Pages 473 through 674. * * * * Yearbook of the Rhododendron Species Foundation, Federal Way, WA. * * * * *


Separate genera

*


Additional resources

Records of the Rhododendron Society of America reside at the Albert and Shirley Small Special Collections Library at the University of Virginia.


External links


History of Rhododendron Discovery & Culture












* ttp://www.vireya.net/ Information on Vireyas
Information+photos of hybrids and species

Information on Rhododendrons by Marc Colombel, founder of the Société Bretonne du Rhododendron.


* ttps://web.archive.org/web/20090130005655/http://www.rhodo.citymax.com/page/page/627471.htm History of Rhododendrons* ttp://www.rododendron.cz/fotogalerie-rododendronu/pruhonicky-park-2011/ Rhododendron in botanical garden Pruhonice-Czech republic


Databases

*
USDA The United States Department of Agriculture (USDA) is the federal executive department responsible for developing and executing federal laws related to farming, forestry, rural economic development, and food. It aims to meet the needs of com ...
Plants Database
''Rhododendron''
*
ITIS The Integrated Taxonomic Information System (ITIS) is an American partnership of federal agencies designed to provide consistent and reliable information on the taxonomy (biology), taxonomy of biological species. ITIS was originally formed in 1 ...
Report
''Rhododendron''

''eFloras.org''
*
Flora of North America: Rhododendron
*
Flora of China: Rhododendron
*
Annotated Checklist of the Flowering Plants of Nepal: Rhododendron


Societies


American Rhododendron Society
*
The Quarterly Bulletin of the American Rhododendron Society 1947–1981
*
Journal of the American Rhododendron Society (JARS) 1982–
** Information Source: .
The Rhododendron, Camellia & Magnolia Group of the Royal Horticultural Society

Rhododendron Species Foundation and Botanical Garden



Australian Rhododendron Society

German Rhododendron Society

New Zealand Rhododendron Association

Danish Rhododendron Society

Fraser South Rhododendron Society


Botanical gardens


Royal Botanic Garden Edinburgh: Rhododendrons at the four Gardens

National Rhododendron Gardens Melbourne Australia
{{Authority control Ericaceae genera Plants used in traditional Chinese medicine National symbols of Nepal Taxa named by Carl Linnaeus Extant Ypresian first appearances