Editing Rhododendron

{{short description|Genus of flowering plants in the heath family Ericaceae}}
{{Other uses}}
{{Use dmy dates|date=January 2020}}
{{Automatic taxobox
| image = Alpenroos.jpg
| image_caption = ''[[Rhododendron ferrugineum]]''
|fossil_range={{fossilrange|52|0}}[[Ypresian]] - present<ref name="Dillhoff2005">{{cite journal |last1=Dillhoff|first1=R. M. |last2=Leopold|first2=E. B. |last3=Manchester|first3=S. R. |year=2005 |title=The McAbee flora of British Columbia and its relations to the Early-Middle Eocene Okanagan Highlands flora of the Pacific Northwest |journal=[[Canadian Journal of Earth Sciences]] |volume=42 |issue=2 |pages=151–166 |doi=10.1139/e04-084|bibcode=2005CaJES..42..151D |url=http://www.fossilmuseum.net/Fossil_Sites/mcabee/mcabeefossils.pdf  |archive-url=https://ghostarchive.org/archive/20221009/http://www.fossilmuseum.net/Fossil_Sites/mcabee/mcabeefossils.pdf |archive-date=2022-10-09 |url-status=live}}</ref>
| display_parents = 2
| taxon = Rhododendron
| authority = [[Carl Linnaeus|L.]]<ref name=LSPR>{{cite book |chapter-url=https://www.biodiversitylibrary.org/item/13829#page/404/mode/1up |last=Linnaeus |first=C. |author-link=Carl Linnaeus |title=Species Plantarum |volume=Tomus I |chapter=Rhododendron |page=392 |year=1753 |publisher=Laurentii Salvii |location=Stockholm |access-date=15 June 2014}}</ref>
| type_species = ''[[Rhododendron ferrugineum]]'' 
| type_species_authority = [[Carl Linnaeus|L.]]
| subdivision_ranks = Subgenera
| subdivision_ref = {{sfnp|Goetsch |Eckert |Hall|2005 |ref=Goetsch}} 
| subdivision =
* ''[[Rhododendron subg. Azaleastrum|Azaleastrum]]''
* ''[[Rhododendron subg. Choniastrum|Choniastrum]]''
* ''[[Rhododendron subg. Hymenanthes|Hymenanthes]]''
* ''[[Rhododendron subg. Rhododendron|Rhododendron]]''
* ''[[Rhododendron subg. Therorhodion|Therorhodion]]''
'''Former subgenera''':<br>
* ''Candidastrum''
* ''Mumeazalea''
* ''[[Rhododendron subg. Pentanthera|Pentanthera]]''
* ''[[Rhododendron subg. Tsutsusi|Tsutsusi]]'' 
|synonyms_ref=<ref>{{cite web |url=https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:327085-2 |title=''Rhododendron'' L. |author=<!--Not stated--> |date=2017 |website=Plants of the World Online |publisher=Board of Trustees of the Royal Botanic Gardens, Kew |access-date=16 September 2020}}</ref>
|synonyms={{collapsible list|
*''Anthodendron'' <small>Rchb.</small>
*''Azaleastrum'' <small>Rydb.</small>
*''× Azaleodendron'' <small>Rodigas</small>
*''Biltia'' <small>Small</small>
*''Candollea'' <small>Baumg.</small>
*''Chamaecistus'' <small>Regel</small>
*''Chamaerhododendron'' <small>Bubani</small>
*''Chamaerhododendros'' <small> Duhamel</small>
*''Diplarche'' <small>Hook.f. & Thomson</small>
*''Dulia'' <small>Adans.</small>
*''Haustrum'' <small>Noronha</small>
*''Hochenwartia'' <small>Crantz</small>
*''Hymenanthes'' <small>Blume</small>
*''Iposues'' <small>Raf.</small>
*''× Ledodendron'' <small>F.de Vos</small>
*''Ledum'' <small>Ruppius ex L.</small>
*''Loiseleria'' <small>Rchb.</small>
*''Menziesia'' <small>Sm.</small>
*''Osmothamnus'' <small>DC.</small>
*''Plinthocroma '' <small>Dulac</small>
*''× Rhodazalea'' <small> Anon.</small>
*''Rhodora'' <small>L.</small>
*''Rhodothamnus'' <small>Lindl. & Paxton</small>
*''Stemotis'' <small>Raf.</small>
*''Theis'' <small>Salisb. ex DC.</small>
*''Therorhodion'' <small>Small</small>
*''Tsusiophyllum'' <small>Maxim.</small>
*''Vireya'' <small>Blume</small>
*''Waldemaria'' <small>Klotzsch</small>
}}}}

'''''Rhododendron''''' ({{IPAc-en|ˌ|r|oʊ|d|ə|ˈ|d|ɛ|n|d|r|ən}}; {{plural form}}: '''''rhododendra''''') 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 species are native to eastern Asia and the [[Himalaya]]n region, but smaller numbers occur elsewhere in Asia, and in North America, Europe and Australia.<ref>{{cite journal | vauthors=Shrestha N|display-authors=etal | year=2018 | title=Global patterns of Rhododendron diversity: The role of evolutionary time and diversification rates | journal=Global Ecology & Biogeography | volume=27 | issue=8 | pages=913–924 | doi=10.1111/geb.12750 |s2cid=92383323 | doi-access=free |bibcode=2018GloEB..27..913S | hdl=10852/67628 | hdl-access=free }}</ref>

It is the [[national flower]] of [[Nepal]], the [[List of U.S. state and territory flowers|state flower]] of [[Washington (state)|Washington]] and [[West Virginia]] in the United States, the state flower of [[Nagaland]] and [[Himachal Pradesh]] in India, the provincial flower of [[Jeju Province]] in South Korea, the provincial flower of [[Jiangxi]] in China and the [[List of Indian state trees|state tree]] of [[Sikkim]] and [[Uttarakhand]] in India. Most species have brightly colored flowers which bloom from late winter through to early summer.<ref>{{cite book |title=Botanica: The Illustrated A-Z of Over 10,000 Garden Plants and How to Cultivate Them |editor-last1=Turner |editor-first1=R.J. Jr. |name-list-style=amp |editor-last2=Wasson |editor-first2=Ernie |date=1997 |page=742}}</ref>

[[Azalea]]s make up two subgenera of ''Rhododendron''. They are distinguished from "true" rhododendrons by having only five [[anther]]s per flower.

== Etymology ==
The common and generic name comes {{etymology|grc|''{{wikt-lang|grc|ῥόδον}}'' {{grc-transl|ῥόδον}}|rose||''{{wikt-lang|grc|δένδρον}}'' {{grc-transl|δένδρον}}|tree}}.<ref>{{OEtymD|rhododendron}}</ref><ref>{{LSJ|r(odo/dendron|ῥοδόδενδρον}}, {{LSJ|r(o/don|ῥόδον}}, {{LSJ|de/ndron|δένδρον|ref}}.</ref><ref>{{cite encyclopedia  |title=rhododendron |dictionary=An etymological dictionary of modern English |page=1234 |url=https://archive.org/details/etymologicaldict00weekuoft/page/616/ |last1=Weekley |first1=Ernest |date=1921 |publisher=London J. Murray }}</ref>

== Description ==
[[File:Найкращі миті життя.jpg|thumb|Rhododendron in the [[Carpathian Mountains]] of Western Ukraine]]
''Rhododendron'' is a genus of [[shrub]]s and small to (rarely) large [[tree]]s, the smallest species growing to {{convert|10|-|100|cm|abbr=on|sigfig=1|round=each}} tall, and the largest, [[Rhododendron protistum|''R. protistum'' var. ''giganteum'']], reported to {{convert|30|m|abbr=on|sigfig=1}} tall.<ref>{{cite web |url=http://www.globaltrees.org/tp_bigtree.htm |title=Big Tree Rhododendron |website=Global Trees Campaign}}</ref><ref>{{cite web |url=http://www.rhododendron-azalee.fr/classification_gb/fiches/protistum_giganteum.shtml |title=''Rhododendron protistum'' var. ''giganteum'' |last=Colombel |first=Marc}}</ref> The [[leaf|leaves]] are spirally arranged; leaf size can range from {{convert|1|-|2|cm|abbr=on|sigfig=1}} to over {{convert|50|cm|abbr=on|sigfig=1}}, exceptionally {{convert|100|cm|abbr=on|sigfig=1}} in [[Rhododendron sinogrande|''R. sinogrande'']]. They may be either [[evergreen]] or [[deciduous]]. 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. A recently discovered species in New Guinea has flowers up to six inches (fifteen centimeters) in width,<ref>{{cite news |  last= Hotz | first= Robert Lee | date= February 7, 2006 | title= A Trove of Unearthly Species....etc | newspaper= Los Angeles Times | page= A8 }} and see:  {{cite journal | url = https://www.scientificamerican.com/article/finding-a-lost-world/ | date = 2006-04-01 | title = Finding a Lost World | author = Charles Q. Choi | journal = [[Scientific American]] | volume = 294 | issue = 4 | pages = 32| doi = 10.1038/scientificamerican0406-32d | bibcode = 2006SciAm.294d..32C }}</ref> the largest in the whole genus. The accompanying photograph shows it as having seven [[petals]].  There are alpine species with small flowers and small leaves, and tropical species such as [[Section (botany)|section]] ''[[Rhododendron sect. Vireya|Vireya]]'' that often grow as [[epiphyte]]s. Species in this genus may be part of the heath complex in [[oak-heath forest]]s in eastern North America.<ref>{{cite web|url=http://www.dcr.virginia.gov/natural_heritage/natural_communities/ncintro.shtml|title=Introduction|website=www.dcr.virginia.gov}}</ref><ref>Schafale, M. P. and A. S. Weakley. 1990. ''Classification of the natural communities of North Carolina: third approximation''. North Carolina Natural Heritage Program, North Carolina Division of Parks and Recreation.</ref>

They have frequently been divided based on the presence or absence of scales on the abaxial (lower) leaf surface ([[lepidote]] or elepidote). These scales, unique to subgenus ''Rhododendron'', are modified hairs consisting of a polygonal scale attached by a stalk.{{sfnp|Goetsch |Eckert |Hall|2005 |ref=Goetsch}}

''Rhododendron'' are characterised by having [[inflorescences]] with scarious (dry) [[Bud|perulae]], a [[chromosome number]] of x=13, [[fruit]] that has a [[septicidal]] [[Capsule (botany)|capsule]], an [[Ovary (botany)|ovary]] that is superior (or nearly so), [[stamens]] that have no appendages, and [[Agglutination (biology)|agglutinate]] (clumped) [[pollen]].{{sfnp|Brown |Craven |Udovicic |Ladiges |2006 |ref=Brown2006}}

== Taxonomy ==
[[File:Ghorepani,_Tadapani,_as_well_as_Mulde_Hill.jpg|thumb|Rhododendrons (Guras) at [[Ghorepani|Ghorepani, Nepal]]]]
[[File:Manaslu-Circuit Rhododendron Forest.jpg|thumb|right|Rhododendron forest in [[Nepal]]]]
[[File:Rhododendron＆Vast ocean of clouds、コバノミツバツツジ＆篠山盆地雲海、盃ヶ岳4256293.JPG|thumb|right|Rhododendron in [[Japan]]]]
[[File:Garden with Rhododendrons.JPG|thumb|right|A garden with tall Rhododendrons in [[Lynnwood, Washington]]]]
[[File:Rhododendron (গুরাস)02.jpg|thumb|Rhododendron (গুরাস), [[Sandakphu|Sandakphu, West Bengal, India]]]]
[[File:Azalea -- Rhododendron.jpg|thumb|Azalea, Texas Gulf Coast]]
[[File:Azalea as a Bonsai (5155648449).jpg|thumb|[[Bonsai]]]]
''Rhododendron'' is the largest genus in the family [[Ericaceae]], with over 1,000 species,<ref name="KewNumberOfSpecies">{{cite web |title=Rhododendrons: Wakehurst's hidden treasure. Rhododendron facts |url=https://www.kew.org/read-and-watch/rhododendrons-at-wakehurst#:~:text=Over%201000%20species%20are%20known%20to%20exist |website=Royal Botanic Gardens Kew |publisher=Board of Trustees of the Royal Botanic Gardens, Kew |access-date=21 May 2022}}</ref><ref>{{cite web |url=http://events.berkeley.edu/index.php/calendar/sn/bot.html?event_ID=73328 |title=Sorting out the Genus Rhododendron: A Taxonomic Overview of this Large Complex of Species |website=University of California Botanical Garden at Berkeley |archive-url=https://web.archive.org/web/20140714150332/http://events.berkeley.edu/index.php/calendar/sn/bot.html?event_ID=73328 |archive-date=14 July 2014}}</ref> (though estimates vary from 850 to 1,200){{sfnp|Fayaz |2012 |page=3 |ref=Fayaz}}<ref name="RSCG-NumberOfSpecies">{{cite web |title=Rhododendron Species Conservation Group |url=https://rscg.org.uk/#:~:text=There%20are%20about%201%2C200%20species%20of%20rhododendron |website=Rhododendron Species Conservation Group |publisher=The Rhododendron Species Conservation Group |access-date=21 May 2022}}</ref> and is [[morphology (biology)|morphologically]] diverse. Consequently, the [[taxonomy (biology)|taxonomy]] has been historically complex.{{sfnp|Brown |Craven |Udovicic |Ladiges |2006 |ref=Brown2006}}

=== 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 [[Carl Linnaeus|Linnaeus]] in his ''[[Species Plantarum]]'' in 1753.<ref name=LSPR/><ref>{{cite book |last=Linnaeus |first=C. |author-link=Carl Linnaeus |title=Genera Plantarum |edition=5th |page=185 |year=1754 |url=https://www.biodiversitylibrary.org/item/14678#page/1/mode/1up |publisher=Laurentii Salvii |location=Stockholm |access-date=1 October 2017}}</ref> He listed five species under ''Rhododendron'': [[Rhododendron ferrugineum|''R.''&nbsp;''ferrugineum'']] (the [[type species]]), ''[[Rhododendron dauricum|R.&nbsp;dauricum]]'', ''[[Rhododendron hirsutum|R.&nbsp;hirsutum]]'', ''R.&nbsp;chamaecistus'' (now ''[[Rhodothamnus chamaecistus]]'' (L.) Rchb.) and ''[[Rhododendron maximum|R.&nbsp;maximum]]''. At that time he considered the then known six species of ''[[Azalea]]''<ref name=LSPA>{{cite book |chapter-url=https://www.biodiversitylibrary.org/item/13829#page/162/mode/1up |last=Linnaeus |first=C. |author-link=Carl Linnaeus |title=Species Plantarum |chapter=Azalea |volume=Tomus I |page=150 |year=1753 |publisher=Laurentii Salvii |location=Stockholm |access-date=15 June 2014}}</ref> that he had described earlier in 1735 in his ''[[Systema Naturae]]'' as a separate genus.<ref name=WIAA>{{cite web |last=Andrews |first=Charles |url=http://azaleachapter.com/plant-info/plants/what-is-an-azalea |publisher=American Rhododendron Society (Azalea Chapter) |title=What is an Azalea?}}</ref><ref name=Spady>{{cite journal |url=http://scholar.lib.vt.edu/ejournals/JARS/v35n4/v35n4-spady.htm |first=Herbert A. |last=Spady |title=GROPING FOR GROUPING: Rhododendron Taxonomy |journal=The Quarterly Bulletin of the American Rhododendron Society |volume=35 |issue=4 |date=Fall 1981}}</ref>

Linnaeus' six species of ''Azalea'' were ''[[Rhododendron indicum|Azalea indica]]'', ''[[Rhododendron luteum|A.&nbsp;pontica]]'', ''[[Rhododendron calendulaceum|A.&nbsp;lutea]]'', ''[[Rhododendron viscosum|A.&nbsp;viscosa]]'', ''[[Rhododendron lapponicum|A.&nbsp;lapponica]]'' and ''A.&nbsp;procumbens'' (now ''[[Kalmia procumbens]]''), which he distinguished from ''Rhododendron'' by having five [[stamens]], 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'' ([[Carl Ludwig Blume|Blume]] 1826)<ref>{{cite web |url=http://www.vireya.net/history.htm |first=Chris |last=Callard |title=The History of Vireya Rhododendron Culture |website=vireya.net |date=1998–2015 |access-date=28 September 2017}}</ref> and ''Hymenanthes'' (Blume 1826) for ''Rhododendron metternichii'', now [[Rhododendron degronianum|R. degronianum]]. Meanwhile, other botanists such as [[Richard Anthony Salisbury|Salisbury]] (1796)<ref>{{cite book |url=https://www.biodiversitylibrary.org/item/9522#page/293/mode/1up |last=Salisbury |first=R.A. |author-link=Richard Anthony Salisbury |title=Prodromus Stirpium in horto ad Chapel Allerton |date=1796 |page=286 |location=London |language=la}}</ref> and Tate (1831)<ref>{{cite book |chapter-url=http://www.british-history.ac.ok/vch/middx/vol12/pp150-155 |chapter=Economic history: Farm-gardening and market gardening |title=A History of the County of Middlesex: Volume 12, Chelsea |editor=Patricia E C Croot |location=London |date=2004 |pages=150–155 |publisher=British History Online}}</ref> began to question the distinction between ''Azalea'' and ''Rhododendron'', and finally in 1836, ''Azalea'' was incorporated into ''Rhododendron''<ref name=Don/> and the genus divided into eight sections. Of these ''Tsutsutsi'' (''[[Rhododendron subg. Tsutsuji|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 {{Nowrap|re-examinations}} of traditional morphological classifications,<ref name=WIAA/><ref name=Spady/> although other authors such as Candolle, who described six sections,{{sfnp|Candolle |1838 |ref=Candolle}} 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''<ref name=Maximovicz/> and [[Jules Émile Planchon|Planchon]]. Maximovicz used flower bud position and its relationship with leaf buds to create eight "Sections".{{sfnp|JIN |DING |ZHANG |HONG |2010 |ref=JDZH}} [[Bentham and Hooker]] used a similar scheme, but called the divisions "Series".<ref name=BH/> It was not until 1893 that [[Bernhard Adalbert Emil Koehne|Koehne]] 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 [[Isaac Bayley Balfour|Balfour]] introduced the concept of grouping species into [[Series (botany)|series]]. ''The Species of Rhododendron''<ref>{{cite book |editor-last=Stevenson |editor-first=J.B. |title=The Species of Rhododendron |publisher=The Rhododendron Society |location=Edinburgh |date=1930}}</ref> referred to this series concept as the Balfourian system. That system continued up to modern times in Davidian's four volume ''The Rhododendron Species''.{{sfnp|Davidian |ref=Davidian}}

=== Modern classification ===
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]], culminating in 1949 with his "Ein System der Gattung ''Rhododendron''"<ref name=Sleumer49>{{cite journal |last=Sleumer |first=H |year=1949 |title=Ein System der Gattung ''Rhododendron'' L. |journal=Bot. Jahrb. Syst. |volume=74 |pages=511–553}}</ref> and subsequent refinements.<ref name=Sleumer66/><ref name=Sleumer80/> 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]] 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'').<ref name=Sleumer80/><ref>{{cite journal |first=J. |last=Cullen |title=A revision of Rhododendron I. Subgenus Rhododendron sections Rhododendron and Pogonanthum |journal=Notes from the Royal Botanic Garden Edinburgh |volume=39 |issue=1 |date=1980 |issn=0080-4274}}</ref> In 1986 Philipson & [[Melva Philipson|Philipson]] raised two sections of subgenus ''Aleastrum'' (''Mumeazalea'', ''Candidastrum'') to subgenera, while reducing genus ''Therorhodion'' to a subgenus of ''Rhododendron''.<ref>{{cite journal |last1=Philipson |first1=W.R. |last2=Philipson |first2=M.N. |year=1986 |title=A revision of Rhododendron III. Subgenera Azaleastrum, Mumeazalea, Candidastrum and Therorhodion |journal=Notes from the Royal Botanic Garden Edinburgh |volume=44 |pages=1–23 |issn=0080-4274}}</ref> In 1987 Spethmann, adding [[phytochemical]] features proposed a system with fifteen subgenera grouped into three 'chorus' subgenera.<ref>{{cite journal |last1=Spethmann |first1=W |year=1987 |title=A new infrageneric classification and phylogenetic trends in the genus ''Rhododendron'' (''Ericaceae'') |journal=Plant Systematics and Evolution |volume=157 |issue= 1–2|pages=9–31 |issn=1615-6110 |doi=10.1007/BF00939178|bibcode=1987PSyEv.157....9S |s2cid=35751500}}</ref>

A number of closely related genera had been included together with ''Rhododendron'' in a former tribe, Rhodoreae. These have been progressively incorporated into ''Rhododendron''.<ref>{{cite journal | last1 = Stevens | first1 = PF | year = 1971| title = A classification of the Ericaceae: subfamilies and tribes | journal = Botanical Journal of the Linnean Society | volume = 64 | issue = 1| pages = 1–53 | doi = 10.1111/j.1095-8339.1971.tb02133.x}}</ref> Chamberlain and Rae moved the [[monotypic]] section ''Tsusiopsis'' together with the monotypic genus ''Tsusiophyllum'' into section ''Tsutsusi'',{{sfnp|Chamberlain |Rae |1990 |ref=ChamRae1990}} while Kron & Judd reduced genus ''[[Ledum]]'' to a subsection of section ''Rhododendron''.<ref>{{cite journal | last1 = Kron | first1 = K. A. | last2 = Judd | first2 = W. S. | year = 1990 | title = Phylogenetic relationships within the Rhodoreae (Ericaceae) with specific comments on the placement of ''Ledum'' | journal = Systematic Botany | volume = 15 | issue = 1| pages = 57–68 | doi=10.2307/2419016| jstor = 2419016| bibcode = 1990SysBo..15...57K }}</ref> Then Judd & Kron moved two species ([[Rhododendron schlippenbachii|''R.''&nbsp;''schlippenbachii'']] and [[Rhododendron quinquefolium|''R.''&nbsp;''quinquefolium'']]) from section ''Brachybachii'', subgenus ''Tsutsusi'' and two from section ''Rhodora'', subgenus ''Pentanthera'' (''[[Rhododendron albrechtii|R.&nbsp;albrechtii]]'', ''[[Rhododendron pentaphyllum|R.&nbsp;pentaphyllum]]'') into section ''Sciadorhodion'', subgenus ''Pentanthera''.<ref>{{cite journal | last1 = Judd | first1 = W. S. | last2 = Kron | first2 = K. A. | year = 1995 | title = A revision of ''Rhododendron''. VI. Subgenus ''Pentanthera'' (sections ''Sciadorhodion'', ''Rhodora'', and ''Viscidula'') | journal = Edinburgh Journal of Botany | volume = 52 | issue = 1| pages = 1–54 | doi=10.1017/s0960428600001906| doi-access = free }}</ref> Finally Chamberlain brought the various systems together in 1996, with 1,025 species divided into eight subgenera. Goetsch (2005) provides a comparison of the Sleumer and Chamberlain schemata (Table&nbsp;1).{{sfnp|Goetsch |Eckert |Hall|2005 |ref=Goetsch}}{{sfnp|Brown |Craven |Udovicic |Ladiges |2006 |ref=Brown2006}}<ref name=Spady/><ref name=Chamberlain/>{{sfnp|Cullen |2005 |ref=Cullen2005}}

===Phylogeny===
{{cladogram
 |align=left
 |title= {{anchor|Clad1}}Cladogram of genus ''Rhododendron'' <br>(Goetsch ''et al.'' 2005)
 |cladogram={{clade
  |style=400px;
  |label1=
  |1={{clade
   |label1=
   |1={{clade
    |label1=
    |1={{clade
     |label1='''{{sc|A}}'''
     |1={{clade
        |1=[[Rhododendron subg. Rhododendron|''Rhododendron'']]
        |2=''[[Choniastrum]]''
        }}
     |label2='''{{sc|B}}'''
     |2=''[[Hymenanthes]]''
     }}
    |label2='''{{sc|C}}'''
    |2=''[[Azaleastrum]]''
    }}
   |2={{clade  |label1=  |1=''[[Therorhodion]]'' }}
   }}
 }}
}}
The era of molecular analysis rather than descriptive features can be dated to the work of Kurashige (1988) and Kron (1997) who used [[Maturase K|matK]] [[sequencing]]. Later Gao ''et al.'' (2002) used [[Internal transcribed spacer|ITS]] sequences<ref name=LianMing/> to determine a [[cladistic]] analysis. They confirmed that the genus ''Rhododendron'' was [[monophyletic]], with subgenus ''Therorhodion'' in the [[Basal (phylogenetics)|basal position]], consistent with the matK studies. Following publication of the studies of Goetsch ''et al.'' (2005) with [[RPB2]],{{sfnp|Goetsch |Eckert |Hall|2005 |ref=Goetsch}} 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.''.{{sfnp|Goetsch |Eckert |Hall|2005 |ref=Goetsch}}<ref name=FSRS>{{cite web |last1=Goetsch |first1=Loretta A.|last2=Eckert |first2=Andrew J. |last3=Hall |first3=Benjamin D. |date=2005 |url=http://www.flounder.ca/FraserSouth/Goetsch-Eckert-Hall.asp |archive-url=https://web.archive.org/web/20130227185832/http://www.flounder.ca/FraserSouth/Goetsch-Eckert-Hall.asp |archive-date=27 February 2013 |website=Fraser South Rhododendron Society |title=Excerpts from and comments on a paper published by: Loretta Goetsch, Andrew Eckert and Benjamin Hall, University of Washington}} 2005 Annual ARS Convention</ref>

The major finding of Goetsch and colleagues was that all species examined (except [[Rhododendron camtschaticum|''R.&nbsp;camtschaticum'']], subgenus ''Therorhodion'') formed three major [[clades]] which they labelled '''{{sc|A}}''', '''{{sc|B}}''', and '''{{sc|C}}''', with the subgenera ''Rhododendron'' and ''Hymenanthes''  as monophyletic groups nested within clades '''{{sc|A}}''' and '''{{sc|B}}''', respectively. By contrast subgenera ''Azaleastrum'' and ''Pentanthera'' were [[polyphyletic]], while ''R.&nbsp;camtschaticum'' appeared as a [[Sister group|sister]] to all other rhododendrons. The small polyphyletic subgenera ''Pentanthera'' and ''Azaleastrum'' were divided between two clades. The four sections of ''Pentanthera'' between clades '''{{sc|B}}''' and '''{{sc|C}}''', with two each, while ''Azaleastrum'' had one section in each of '''{{sc|A}}''' and '''{{sc|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]]'', ''Tsusiophyllum''), Goetsch ''et al.''. added ''[[Menziesia]]'' (clade '''{{sc|C}}'''). Despite a degree of [[paraphyly]], 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 '''{{sc|B}}''' (''Hymenanthes'') and '''{{sc|C}}''' (''Azaleastrum''), although the name was retained in section ''Pentanthera'' (14&nbsp;species) which was moved to subgenus ''Hymenanthes''. Of the remaining three sections, monotypic ''Viscidula'' was discontinued by moving [[Rhododendron nipponicum|''R.''&nbsp;''nipponicum'']] to ''Tsutsusi'' ('''{{sc|C}}'''), while ''Rhodora'' (2&nbsp;species) was itself polyphyletic and was broken up by moving [[Rhododendron canadense|''R.''&nbsp;''canadense'']] to section ''Pentanthera'' ('''{{sc|B}}''') and [[Rhododendron vaseyi|''R.''&nbsp;''vaseyi'']] to section ''Sciadorhodion'', which then became a new section of subgenus ''Azaleastrum''&nbsp;('''{{sc|C}}''').

Subgenus ''Tsutsusi'' ('''{{sc|C}}''') was reduced to section status retaining the name, and included in subgenus ''Azaleastrum''. Of the three minor subgenera, all in '''{{sc|C}}''', two were discontinued. The single species of [[monotypic]] subgenus ''Candidastrum'' ([[Rhododendron albiflorum|''R.''&nbsp;''albiflorum'']]) was moved to subgenus ''Azaleastrum'', section ''Sciadorhodion''. Similarly the single species in monotypic subgenus ''Mumeazalea'' ([[Rhododendron semibarbatum|''R.''&nbsp;''semibarbatum'']]) was placed in the new section ''Tsutsusi'', subgenus ''Azaleastrum''. Genus ''Menziesa'' (9&nbsp;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&nbsp;'''{{sc|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.{{sfnp|Goetsch |Eckert |Hall|2005 |ref=Goetsch}} (See schemata under [[#Subgenera|''Subgenera'']].)<ref name=FSRS/>

{| class="wikitable" style="width:500px;"
|+ <big>Taxonomic changes within genus ''Rhododendron''</big>
! style="border-right:solid black 2px; background: #ccf" colspan=4|Chamberlain (1996)||style="background: #ccf" colspan=2|Goetsch (2005)
|-
! style="background:#ccf" |Genus ||style="background:#ccf" |Subgenus ||style="background:#ccf" |Section ||style="border-right:solid black 2px; background:#ccf" |Species ||style="background:#ccf" |Subgenus ||style="background:#ccf" |Section
|-
| ''Menziesa'' ||   ||   ||style="border-right:solid black 2px"| 9&nbsp;species ||style="text-align:center;" rowspan=4|''Azaleastrum''<br/>'''{{sc|C}}'''||rowspan=4|''Sciadorhodion''
|-
| rowspan=10| ''Rhododendron'' || ''Candidastrum'' ||   ||style="border-right:solid black 2px"|''R.&nbsp;albiflorum''
|-
| rowspan=5| ''Pentanthera'' || ''Sciadorhodion'' ||style="border-right:solid black 2px"| 4&nbsp;species
|-
| rowspan=2| ''Rhodora'' ||style="border-right:solid black 2px"|''R.&nbsp;vaseyi''
|-
| style="border-right:solid black 2px"|''R.&nbsp;canadense'' ||style="text-align:center;" rowspan=2|''Hymenanthes''<br/>'''{{sc|B}}'''||rowspan=2|''Pentanthera''
|-
| ''Pentanthera'' ||style="border-right:solid black 2px"| 14&nbsp;species
|-
| ''Viscidula'' ||style="border-right:solid black 2px"| ''R.&nbsp;nipponicum'' ||style="text-align:center;" rowspan=4|''Azaleastrum''<br/>'''{{sc|C}}'''||rowspan=4|''Tsutsusi''
|-
| rowspan=2| ''Tsutsusi'' || ''Brachycalyx'' ||style="border-right:solid black 2px"| 15&nbsp;species
|-
| ''Tsutsusi'' ||style="border-right:solid black 2px"| 65&nbsp;species
|-
| ''Mumeazalea'' ||   ||style="border-right:solid black 2px"|''R.&nbsp;semibarbatum''
|-
| ''Azaleastrum'' || ''Choniastrum'' ||style="border-right:solid black 2px"| 11&nbsp;species ||style="text-align:center;"| ''Choniastrum''<br/>'''{{sc|A}}'''
|}

Subsequent research has supported the revision by Goetsch, although has largely concentrated on further defining the phylogeny within the subdivisions.{{sfnp|Craven |Goetsch |Hall |Brown |2008 |ref=Craven2008}} In 2011 the two species of ''Diplarche'' were also added to ''Rhododendron'', ''[[incertae sedis]]''.{{sfnp|Craven|2011 |ref=Craven2011}}

===Subdivision===
This genus has been progressively subdivided into a hierarchy of subgenus, section, subsection, and species.

====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]],{{sfnp|Genus Rhododendron Taxonomic Tree |ref=ARS2}} ''Rhododendron'' has eight subgenera based on [[Morphology (biology)|morphology]], namely the presence of scales (lepidote), [[deciduousness]] of leaves, and the floral and vegetative branching patterns, after Sleumer (1980).{{sfnp|Goetsch |Eckert |Hall|2005 |ref=Goetsch}}{{sfnp|Brown |Craven |Udovicic |Ladiges |2006 |ref=Brown2006}}<ref name=Sleumer80/> 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.<ref name="ARS1"/> The largest of these is subgenus ''Rhododendron'', containing nearly half of all known species and all of the lepidote species.

*Subgenus ''[[Rhododendron subg. Rhododendron|Rhododendron]]'' {{small|L.}}: Small leaf or [[lepidotes]] (scales on the underside of the leaves). 3 sections, 462 species, [[type species]]: ''R.&nbsp;ferrugineum''.
*Subgenus ''[[Rhododendron subg. Hymenanthes|Hymenanthes]]'' {{small|(Blume) K.Koch}}: Large leaf or [[elepidotes]] (without scales). 1 section, 224 species, type [[Rhododendron degronianum|''R.''&nbsp;''degronianum'']].
*Subgenus ''[[Rhododendron subg. Pentanthera|Pentanthera]]'' {{small|(G. Don) Pojarkova}}: Deciduous azaleas. 4 sections, 23 species, type [[Rhododendron luteum|''R.''&nbsp;''luteum'']].
*Subgenus ''[[Rhododendron sect. Tsutsusi|Tsutsusi]]'' {{small|(Sweet) Pojarkova}}: Evergreen azaleas. 2 sections, 80 species, type [[Rhododendron indicum|''R.''&nbsp;''indicum'']].
*Subgenus ''[[Rhododendron subg. Azaleastrum|Azaleastrum]]'' {{small|Planch.}}: 2 sections, 16 species, type ''[[Rhododendron ovatum|R. ovatum]]''.
*Subgenus ''Candidastrum'' {{small|[[Franch.]]}}: 1 species, ''[[Rhododendron albiflorum|R. albiflorum]]''.
*Subgenus ''Mumeazalea'' {{small|(Sleumer) W.R. Philipson & M.N. Philipson}}: 1 species, ''[[Rhododendron semibarbatum]]''.
*Subgenus ''Therorhodion'' {{small|(Maxim.) A. Gray}}: 2 species (''[[Rhododendron camtschaticum]]'', ''[[Rhododendron redowskianun]]'').

For a comparison of the Sleumer and Chamberlain systems, see Goetsch ''et al.'' (2005) Table 1.{{sfnp|Goetsch |Eckert |Hall|2005 |ref=Goetsch}}

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]] from previous year's shoots or the lowest scaly leaves.

[[File:Rhododendron luteum BotGardBln1105Autumn.JPG|thumb|right|Deciduous ''Rhododendron luteum'' in fall color]]
[[File:Rhododendron kaempferi 08.jpg|thumb|Evergreen azalea ''Rhododendron kaempferi'']]
[[File:2014-10-29 13 26 34 Evergreen Rhododendron foliage coloring before being shed in Ewing, New Jersey.JPG|thumb|right|Evergreen azalea cultivar leaf color before shedding]]
[[File:Rhododendron after freezing rain.jpg|thumb|right|Rhododendron after [[freezing rain]]]]
{| class="wikitable"
|+ <big>Morphological classification of ''Rhododendron'' </big><br>(Chamberlain 1996)<ref name=Chamberlain/>
! style="background:#ccf" |Inflorescence buds !!style="background:#ccf" |Leaf scales !!style="background:#ccf" |Leaf shoots !!style="border-right:solid black 2px; background:#ccf" |Leaves !!style="background:#ccf" |Subgenus !!style="background:#ccf" |Section
|-
|rowspan=7| Terminal ||colspan=3|Present ||style="border-left:solid black 2px"|''[[Rhododendron subg. Rhododendron|Rhododendron]]''
|-
| rowspan=6 |Absent||rowspan=4|Previous year||style="border-right:solid black 2px" |Evergreen||''[[Rhododendron subg. Hymenanthes|Hymenanthes]]''
|-
| rowspan=3 style="border-right:solid black 2px"|Deciduous||rowspan=3|''[[Rhododendron subg. Pentanthera|Pentanthera]]'' ||''Pentanthera''
|-
| ''Rhodora''
|-
| ''Viscidula''
|-
|rowspan=2 colspan=2|Lowest leaves|| style="border-left:solid black 2px"|''Pentanthera''||''Sciadorhodion''
|-
| style="border-left:solid black 2px"|''[[Rhododendron sect. Tsutsusi|Tsutsusi]]''
|-
|rowspan=4 colspan=3|Lateral|| style="border-right:solid black 2px"|Evergreen||''[[Rhododendron subg. Azaleastrum|Azaleastrum]]''
|-
| rowspan=3 style="border-right:solid black 2px"|Deciduous||''Candidastrum''
|-
| ''Mumeazalea''
|-
|''Therorhodion''
|}

Following the [[cladistic analysis]] of Goetsch ''et al.'' (2005){{sfnp|Goetsch |Eckert |Hall|2005 |ref=Goetsch}} this scheme was simplified, based on the discovery of three major [[clade]]s (A, B, C) as follows.

'''Clade A'''
* Subgenus ''[[Rhododendron subg. Rhododendron|Rhododendron]]'' {{Small|L.}}: Small leaf or [[lepidotes]] (scales on the underside of the leaves). 3 sections, about 400 species, [[type species]]: ''R.''&nbsp;''ferrugineum''.
* Subgenus ''[[Rhododendron subg. Choniastrum|Choniastrum]]'' {{Small|Franch.}}: 11 species
'''Clade B'''
* Subgenus ''[[Rhododendron subg. Hymenanthes|Hymenanthes]]'' {{Small|(Blume) K.Koch}}: Large leaf or [[elepidotes]] (without scales), including deciduous azaleas. 2 sections, about 140–225 species, type ''[[Rhododendron degronianum|R. degronianum]]''.
'''Clade C'''
* Subgenus ''[[Rhododendron subg. Azaleastrum|Azaleastrum]]'' {{Small|Planch.}}: Evergreen azaleas. 3 sections, about 120 species, type ''[[Rhododendron ovatum]]''.
'''[[Sister taxon]]'''
* Subgenus ''Therorhodion'' {{Small|(Maxim.) A. Gray}}: 2 species (''[[Rhododendron camtschaticum|R. camtschaticum]]'' and ''[[Rhododendron redowskianun|R. redowskianun]]'').

==== Sections and subsections ====
The larger subgenera are further subdivided into sections and subsections<ref name="ARS1">{{cite web |url=http://www.rhododendron.org/v47n3p139.htm |title=Concerning the Origin and Distribution of Rhododendrons |last=Irving |first=E. |author2=R. Hebda |year=1993 |work=Journal of the American Rhododendron Society |publisher=American Rhododendron Society |access-date=4 November 2012}}</ref> 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){{sfnp|Goetsch |Eckert |Hall|2005 |ref=Goetsch}} and by Craven ''et al.'' (2008){{sfnp|Craven |Goetsch |Hall |Brown |2008 |ref=Craven2008}} 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{{sfnp|Genus Rhododendron Taxonomic Tree |ref=ARS2}}

*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 (section)|Rhododendron]]'' L. (149 species in 25 subsections; temperate to subarctic Northern Hemisphere)
**''[[Rhododendron subgenus Vireya|Vireya]]'' (Blume) Copel.f. (300 species in 2 subsections; tropical southeast Asia, Australasia. At one time considered separate subgenus{{sfnp|Argent|2006 |ref=Argent2006}})
*Subgenus ''[[Rhododendron subg. Hymenanthes|Hymenanthes]]'' (Blume) K.Koch (1 section, 224 species) (''Increased to two sections'')
**''Ponticum'' {{small|G. Don}} (24 subsections)
**(''[[Rhododendron sect. Pentanthera|Pentanthera]]'' {{small|(G. Don) Pojarkova}} (2 subsections – new section, moved from subgenus ''Pentanthera'')
*Subgenus ''Pentanthera'' {{small|(G. Don) Pojarkova}} (4 sections, 23 species) (''Discontinued'')
**''[[Rhododendron sect. Pentanthera|Pentanthera]]'' {{small|(G. Don) Pojarkova}} (2 subsections – moved to subgenus ''Hymenanthes'')
**''[[Rhododendron sect. Rhodora|Rhodora]]'' (L.) G. Don (2 species; ''[[Rhododendron canadense]]'', ''[[Rhododendron vaseyi]]'') (''Discontinued, redistributed'')
**''[[Rhododendron sect. Sciadorhodion|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)'')

The system used by the [[World Flora Online]] {{As of|2023|December|lc=yes}} uses six subgenera, four of which are divided further:<ref name=WFO_4000033027>{{cite web |author=WFO |date=December 2023 |title=''Rhododendron'' L.. |work=World Flora Online |url=https://list.worldfloraonline.org/wfo-4000033027 |access-date=2024-02-22}}</ref>
*[[Rhododendron subg. Azaleastrum|subgenus ''Azaleastrum'']] {{small|Planch. ex K.Koch}}<ref name=WFO_1000040525>{{cite web |author=WFO |date=December 2023 |title=''Rhododendron'' subg. ''Azaleastrum'' Planch. ex K.Koch |work=World Flora Online |url=https://list.worldfloraonline.org/wfo-1000040525 |access-date=2024-02-22}}</ref>
**[[Rhododendron sect. Azaleastrum|section ''Azaleastrum'']] {{small|Planch. ex Maxim.}}
**[[Rhododendron sect. Sciadorhodion|section ''Sciadorhodion'']] {{small|Rehder & E.H.Wilson}}
**[[Rhododendron sect. Tsutsutsi|section ''Tsutsutsi'']] {{small|(Sweet) Pojark.}}
*[[Rhododendron subg. Choniastrum|subgenus ''Choniastrum'']] {{small|Franch.}}
*[[Rhododendron subg. Hymenanthes|subgenus ''Hymenanthes'']] {{small|(Blume) K.Koch}}<ref name=WFO_1000040538>{{cite web |author=WFO |date=December 2023 |title=''Rhododendron'' subg. ''Hymenanthes'' (Blume) K.Koch |work=World Flora Online |url=https://list.worldfloraonline.org/wfo-1000040538 |access-date=2024-02-22}}</ref>
**[[Rhododendron sect. Pentanthera|section ''Pentanthera'']] {{small|G.Don}}
**[[Rhododendron sect. Ponticum|section ''Ponticum'']] {{small|G.Don}}
**[[Rhododendron sect. Rhodora|section ''Rhodora'']] {{small|(L.) G.Don}}
*[[Rhododendron subg. Rhododendron|subgenus ''Rhododendron'']] {{small|L.}}<ref name=WFO_3500001788>{{cite web |author=WFO |date=December 2023 |title=''Rhododendron'' subg. ''Rhododendron'' L.. |work=World Flora Online |url=https://list.worldfloraonline.org/wfo-3500001788 |access-date=2024-02-22}}</ref>
**[[Rhododendron sect. Pogonanthum|section ''Pogonanthum'']] {{small|G.Don}}
**[[Rhododendron sect. Rhododendron|section ''Rhododendron'']] {{small|}}
*[[Rhododendron subg. Therorhodion|subgenus ''Therorhodion'']] {{small|(Maxim) Rehder}}
*[[Rhododendron subg. Vireya|subgenus ''Vireya'']] {{small|Clarke}}<ref name=WFO_3500001320>{{cite web |author=WFO |date=December 2023 |title=''Rhododendron'' subg. ''Vireya'' L.. |work=World Flora Online |url=https://list.worldfloraonline.org/wfo-3500001320 |access-date=2024-02-22}}</ref>
**[[Rhododendron sect. Albovireya|section ''Albovireya'']] {{small|(Sleumer) Argent}}
**[[Rhododendron sect. Discovireya|section ''Discovireya'']] {{small|(Sleumer) Argent}}
**[[Rhododendron sect. Hadranthe|section ''Hadranthe'']] {{small|Schltr.}}
**[[Rhododendron sect. Malayovireya|section ''Malayovireya'']] {{small|(Sleumer) Argent}}
**[[Rhododendron sect. Pseudovireya|section ''Pseudovireya'']] {{small|(Clarke) Sleumer}}
**[[Rhododendron sect. Schistanthe|section ''Schistanthe'']] {{small|Schltr.}}
**[[Rhododendron sect. Siphonovireya|section ''Siphonovireya'']] {{small|Argent}}

=== Species ===
{{further|List of Rhododendron species}}

== Distribution and habitat ==
[[File:Rhododendron fallacinum (cropped).jpg|thumb|upright|''[[Rhododendron fallacinum]]'' photographed ''in situ'' on [[Mount Kinabalu]], [[Borneo]]]]
Species of the genus ''Rhododendron'' are widely distributed between latitudes 80°N and 20°S and are [[native plant|native]] to areas from North America to [[Europe]], [[Russia]], and [[Asia]], and from [[Greenland]] to [[Queensland]], [[Australia]] and the [[Solomon Islands]].{{sfnp|Brown |Craven |Udovicic |Ladiges |2006 |ref=Brown2006}} The [[center of diversity|centres of diversity]] are in the [[Himalayas]] and [[Maritime Southeast Asia]],<ref name=LianMing>{{cite journal |author1=GAO Lian-Ming |author2=LI De-Zhu |author3=ZHANG Chang-Qin |author4=YANG Jun-Bo | year = 2002 | title = Infrageneric and Sectional Relationships in the Genus Rhododendron (Ericaceae) Inferred from ITS Sequence Data | url = http://www.jipb.net/pubsoft/content/2/2316/X010407(PS2).pdf | journal = Am Botanica Sinica | volume = 44 | issue = 11| pages = 1351–1356}}</ref> with the greatest species diversity in the Sino-Himalayan region, Southwest China and northern [[Burma]], from India – [[Himachal Pradesh]], [[Uttarakhand]], [[Sikkim]] and [[Nagaland]] to [[Nepal]], northwestern [[Yunnan]] and western [[Sichuan]] and southeastern [[Tibet]]. Other significant areas of diversity are in the mountains of [[Korea]], [[Japan]] and [[Taiwan]]. 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).{{sfnp|Goetsch |Eckert |Hall|2005 |ref=Goetsch}}

The 300 [[Tropical climate|tropical]] species within the ''[[Rhododendron sect. Vireya|Vireya]]'' section of subgenus ''Rhododendron'' occupy the [[Maritime Southeast Asia]] from their presumed Southeast Asian origin to Northern Australia, with 55 known species in [[Borneo]] and 164 in [[New Guinea]]. The species in New Guinea are native to [[Subalpine zone|subalpine]] moist [[grasslands]] at around 3,000 metres above sea level in the Central Highlands.{{sfnp|Argent|2006 |ref=Argent2006}} 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]]. Subgenus ''Tsutsusi'' is found in the maritime regions of [[East Asia]] (Japan, Korea, Taiwan, [[East China]]), but not in North America or Eurasia.{{sfnp|Goetsch |Eckert |Hall|2005 |ref=Goetsch}}{{sfnp|JIN |DING |ZHANG |HONG |2010 |ref=JDZH}}

In the United States, native ''Rhododendron'' mostly occur in lowland and montane forests in the [[Pacific Northwest]], [[California]], the [[Northeastern United States|Northeast]], and the [[Appalachian Mountains]].<ref>Irving, E., & Hebda, R. (1993). Concerning the Origin and Distribution of Rhododendrons. ''Journal American Rhododendron Society'', ''47''(3).</ref>

==Ecology==
===Invasive species===
''[[Rhododendron ponticum]]'' has become invasive in [[Republic of Ireland|Ireland]]<ref>{{cite news |url=http://www.irishcentral.com/news/Dramatic-rescue-of-couple-trapped-in-rhododendron-forest.html |title=Dramatic rescue of couple trapped in rhododendron forest |website=Irish Central |date=18 July 2014 |last=Bramhill |first=Nick}}</ref> and the [[United Kingdom]].<ref>{{cite news |url=https://www.theguardian.com/science/2017/apr/16/rhododendron-ponticum-thug-invasive-out-of-control-plantwatch |title=A spectacular thug is out of control |website=The Guardian |date=16 April 2017 |last=Simons |first=Paul |access-date=2 October 2017}}</ref> 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]]s are major pests of rhododendrons, and many [[caterpillar]]s will preferentially devour them.

''Rhododendron'' species are used as food plants by the [[larva]]e ([[caterpillars]]) of some [[butterflies]] and [[moths]]; see List of Lepidoptera that feed on rhododendrons.

===Diseases===
{{Main|List of rhododendron diseases}}
Major diseases include ''[[Phytophthora]]'' root rot, stem and twig fungal dieback.<ref>{{cite web|url=http://www.ag.ohio-state.edu/~ohioline/hyg-fact/3000/3043.html |title=Maintaining Healthy Rhododendrons and Azaleas in the Landscape |first1=Harry A. J. |last1=Hoitink |first2=Stephen |last2=Nameth |first3=Jim |last3=Chatfield |website=ohioline.ag.ohio-state.edu |access-date=26 February 2013 |archive-url=https://web.archive.org/web/20130605225226/http://ohioline.osu.edu/hyg-fact/3000/3043.html |archive-date=5 June 2013}}</ref>

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''.<ref name=AHSEG>{{cite book |title=The American Horticultural Society Encyclopedia of Gardening |editor1-first=Christopher |editor1-last=Brickell |editor2-first=Elvin |editor2-last=McDonald |location=NY |publisher=Dorling Kindersley Publishing |date=1993 |isbn=978-1564582911 |url=https://archive.org/details/americanhorticul00bric}}</ref>{{rp|page=562}}

== Conservation ==
In the UK the forerunner of the Rhododendron, Camellia and Magnolia Group (RCMG), The Rhododendron Society was founded in 1916.<ref>{{cite web |title=Centenary – Background |url=http://www.rhodogroup-rhs.org/centenary/background/ |archive-url=https://web.archive.org/web/20160912182235/http://www.rhodogroup-rhs.org/centenary/background/ |archive-date=12 September 2016 |access-date=26 May 2016 |publisher=Rhododendron, Camellia and Magnolia Group}}</ref> while in Scotland species are being conserved by the Rhododendron Species Conservation Group.<ref>{{cite web |author=John M. Hammond |title=Conservation of Rhododendron Species and their historic Gardens |url=http://www.rscg.org.uk/ |access-date=2 October 2017 |publisher=RSCG}}</ref>

== Cultivation ==
[[File:Rhododendronpark Bremen 14-05-09.jpg|thumb|right|[[Rhododendron-Park Bremen]], Germany]]
Both species and hybrid rhododendrons (including azaleas) are used extensively as [[ornamental plant]]s in [[landscaping]] in many parts of the world, including both [[temperate]] and [[wiktionary:subtemperate|subtemperate]] regions.{{sfnp|Craven |Goetsch |Hall |Brown |2008 |ref=Craven2008}} Many species and cultivars are grown commercially for the [[Nursery (horticulture)|nursery]] trade.

Rhododendrons can be propagated by air layering or stem cuttings.<ref name=AHSEG/>{{rp|540–541}} 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. They can also be reproduced by seed dispersal or by horticulturalists collecting the spent flower buds and saving and drying the seed for later germination and planting.

[[File:Rhododendron wardii var puralbum.jpg|thumb|right|''Rhododendron wardii'' var. ''puralbum'']]
Rhododendrons are often valued in landscaping for their structure, size, flowers, and the fact that many of them are evergreen.<ref name=Huxley>{{cite book |editor1=Huxley, A. |editor2=Griffiths, M. |editor3=Levy, Margot |date=1992 |title=New RHS Dictionary of Gardening |publisher=Macmillan |location=London |isbn=978-0333474945}}</ref> 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]]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]]'' and ''[[Rhododendron falconeri|R.&nbsp;falconeri]]'' eventually growing to a height of {{convert|10|-|15|m|ft|2|abbr=on}} or more.<ref name=Huxley/>

===Commercial growing===
Rhododendrons are grown commercially in many areas for sale, and seeds were occasionally collected in the wild, a practice now rare in most areas due to the [[Nagoya Protocol]]. 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.<ref name=Cox1993/>

===Horticultural divisions===
Horticulturally, rhododendrons may be divided into the following groups:<ref name=WIAA/><ref>{{cite book |title=RHS A-Z Encyclopedia of Garden Plants |year=2008 |editor-first=Christopher |editor-last=Brickell |publisher=Penguin Books |location=United Kingdom |isbn=978-1405332965 |page=1136}}</ref>
* Evergreen rhododendrons - large group of evergreen shrubs that vary greatly in size. Most rhododendron flowers are bell-shaped and have 10 stamens.
* [[Rhododendron sect. Vireya|Vireya]] ([[Malesia]]n) rhododendrons: [[epiphyte|epiphytic]] [[hardiness (plants)|tender]] shrubs<ref>{{cite web|url=http://www.vireya.net/ |first=Chris |last=Callard |title=Vireya Rhododendrons – Welcome |publisher=vireya.net |date=1998–2015 |access-date=26 February 2013}}</ref>
* [[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:<ref>{{cite web|url=http://www.rhodyman.net/rhodyde.html |title=Deciduous Azaleas |publisher=Rhodyman.net |access-date=26 February 2013}}</ref>
*** Exbury hybrids – derived from the Knap Hill hybrids, developed by [[Lionel de Rothschild (born 1882)|Lionel de Rothschild]] at the [[Exbury Gardens|Exbury Estate]] in England.<ref name=DHKnapHill>{{cite web|url=http://www.tjhsst.edu/~dhyatt/knaphill.html |title=My Fascination with Knap Hill Azaleas |last=Hyatt |first=Donald W. |access-date=24 September 2017}}</ref><ref>{{cite web|url=https://www.tjhsst.edu/~dhyatt/trip/exbury.html |title=Exbury Gardens |last=Hyatt |first=Donald W. |access-date=21 October 2017}}</ref>
*** Ghent (Gandavense) hybrids – Belgian raised<ref name=Skinner>{{cite journal |url=http://scholar.lib.vt.edu/ejournals/JARS/v38n3/v38n3-skinner.htm |title=Rescuing the Ghent and Rustica Flore Pleno Azaleas |journal=Journal American Rhododendron Society |volume=38 |issue=3 |last=Skinner |first=Archie |date=Summer 1984 |access-date=26 February 2013}}</ref>
*** Knap Hill hybrids – developed by Anthony Waterer at the [[Knaphill|Knap Hill]] Nursery in England.<ref name=DHKnapHill/>
*** Mollis hybrids – Dutch and Belgian raised<ref>{{cite journal |url=http://scholar.lib.vt.edu/ejournals/JARS/v14n1/v14n1-living.htm |journal=The Quarterly Bulletin of the American Rhododendron Society |volume=14 |issue=1 |last=Living |first=L.C. |title=Mollis Azaleas |date=January 1960 |access-date=26 February 2013}}</ref>
*** New Zealand Ilam hybrids – derived from Knap Hill/Exbury hybrids
*** Occidentale hybrids – English raised
*** Rustica Flore Pleno hybrids – sweet-scented, double-flowered<ref name=Skinner/>
** Evergreen hybrid azaleas:
*** Gable hybrids – raised by Joseph B. Gable in [[Pennsylvania]].<ref>{{cite web|url=http://www.tjhsst.edu/~dhyatt/gable.html |title=The Rhododendron Legacy of Joe Gable |last=Hyatt |first=Donald W. |access-date=24 September 2017}}</ref>
*** 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&nbsp;°C)
*** Oldhamii hybrids – dwarf hybrids raised at [[Exbury]], England
*** Satsuki hybrids – Japanese raised, originally for [[bonsai]]
*** Shammarello hybrids – raised in northern [[Ohio]]<ref>{{cite journal |url=http://scholar.lib.vt.edu/ejournals/JARS/v9n4/v9n4-baldsiefen.htm |journal=The Quarterly Bulletin of the American Rhododendron Society |volume=9 |issue=4 |last=Baldsiefen |first=Warren |title=Shammarello's Wonderland |date=October 1955 |access-date=26 February 2013}}</ref>
*** Vuyk (Vuykiana) hybrids – raised in the Netherlands<ref>{{cite journal |url=http://scholar.lib.vt.edu/ejournals/JARS/v33n1/v33n1-nosal.htm |journal=The Quarterly Bulletin of the American Rhododendron Society |volume=33 |issue=1 |last=Nosal |first=Mathew A. |title=The Vuykiana Azaleas |date=Winter 1979 |access-date=26 February 2013}}</ref>
* Azaleodendrons – semi-evergreen hybrids between deciduous azaleas and rhododendrons

===Planting and care===
[[File:Nova Zembla Rhododendron plants growing in NJ in April.jpg|thumb|right|Nova Zembla Rhododendrons growing in a nursery in [[New Jersey]].]]
Like other [[Ericaceae|ericaceous]] plants, most rhododendrons prefer acid soils with a pH of roughly 4.5–5.5; some tropical Vireyas and a few other rhododendron species grow as [[epiphyte]]s and require a planting mix similar to [[orchids]]. Rhododendrons have fibrous roots and prefer well-drained soils high in organic material. In areas with poorly drained or alkaline soils, rhododendrons are often grown in raised beds using media such as composted pine bark.<ref>{{cite web|url=http://www.rhododendron.org/soil.htm |title=Soil information for planting rhododendrons |work=American Rhododendron Society |access-date=26 February 2013}}</ref> Mulching and careful watering are important, especially before the plant is established.

A new [[calcifuge|calcium-tolerant]] stock of rhododendrons (trademarked as 'Inkarho') has been exhibited at the [[Royal Horticultural Society|RHS]] [[Chelsea Flower Show]] in London (2011). Individual hybrids of rhododendrons have been [[grafting|grafted]] on to a [[rootstock]] 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.<ref>{{cite web |url=https://www.rhododendrons.co.uk/rhododendrons/lime-tolerant-rhododendrons.aspx |title=Lime Tolerant Rhododendrons |publisher=Millais Nurseries |access-date=2 October 2017}}</ref><ref>{{cite news |first=Bunny |last=Guinness |date=17 November 2009 |url=https://www.telegraph.co.uk/gardening/6581138/The-new-lime-tolerant-rhododendrons.html |title=The new lime-tolerant rhododendrons |newspaper=The Telegraph |access-date=26 February 2013}}</ref>

===Hybrids===
Rhododendrons are extensively hybridized in cultivation, and natural hybrids often occur in areas where species ranges overlap. There are over 28,000 [[cultivar]]s of Rhododendron in the International Rhododendron Registry held by the [[Royal Horticultural Society]]. Most have been bred for their flowers, but a few are of garden interest because of ornamental leaves and some for ornamental bark or stems. Some hybrids have fragrant flowers<ref>{{cite web|title=Fragrant Rhododendrons|url=http://plants.wildeel.com/rhodofrag.html |last=Francis |first=Richard |website=Wildeel.com |access-date=11 March 2015|date=25 January 2006 |archive-url=https://web.archive.org/web/20150708084734/http://plants.wildeel.com/rhodofrag.html |archive-date=8 July 2015}}</ref>—such as the Loderi hybrids, created by crossing ''[[Rhododendron fortunei]]'' and ''[[Rhododendron griffithianum|R.&nbsp;griffithianum]]''.{{sfnp|Davidian |loc=Vol. II, plate 44 & 45 |ref=Davidian}} Other examples include the PJM hybrids, formed from a cross between ''[[Rhododendron carolinianum]]'' and ''[[Rhododendron dauricum|R.&nbsp;dauricum]]'', and named after Peter J. Mezitt of Weston Nurseries, Massachusetts.<ref>{{cite web |first=Mark H. |last=Brand |url=http://www.hort.uconn.edu/plants/r/rhopjm/rhopjm1.html |website=UConn Plant Database |title=Rhododendron 'PJM' Hybrids |archive-url=https://web.archive.org/web/20130629153207/http://www.hort.uconn.edu/plants/r/rhopjm/rhopjm1.html |archive-date=29 June 2013}}</ref>

== Toxicity ==
{{Main|Grayanotoxin}}

Some species of rhododendron are poisonous to grazing animals because of a [[toxin]] called [[grayanotoxin]] in their [[pollen]] and [[nectar (plant)|nectar]]. People have been known to become ill from eating [[mad honey]] made by [[bee]]s feeding on rhododendron and [[azalea]] flowers. [[Xenophon]] described the odd behaviour of [[Greeks|Greek]] soldiers after having consumed honey in a village surrounded by ''[[Rhododendron ponticum]]'' during the march of the [[Ten Thousand (Greek)|Ten Thousand]] in 401&nbsp;BCE.<ref>Xenophon, ''[[Anabasis (Xenophon)|Anabasis]]'' 4.8.19–21.</ref> [[Pompey]]'s soldiers reportedly suffered lethal casualties following the consumption of [[mad honey|honey made from ''Rhododendron'']] deliberately left behind by [[Pontic Greeks|Pontic]] forces in 67&nbsp;BCE during the [[Third Mithridatic War]].<ref>[[Strabo]], ''[[Geographica|Geography]]'' 12.3.18.</ref> Later, it was recognized that honey resulting from these plants has a slightly [[hallucinogenic]] and [[laxative]] effect.<ref>{{cite book |title=Bad Bug Book: Handbook of foodborne pathogenic microorganisms and natural toxins |publisher=Food and Drug Administration |year=2012 |edition=2nd |chapter=Grayanotoxins |access-date=3 October 2017 |chapter-url=https://www.fda.gov/downloads/food/foodsafety/foodborneillness/foodborneillnessfoodbornepathogensnaturaltoxins/badbugbook/ucm297627.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://www.fda.gov/downloads/food/foodsafety/foodborneillness/foodborneillnessfoodbornepathogensnaturaltoxins/badbugbook/ucm297627.pdf |archive-date=2022-10-09 |url-status=live}}</ref> The suspect rhododendrons are ''[[Rhododendron ponticum]]'' and ''[[Rhododendron luteum]]'' (formerly ''Azalea pontica''), both found in northern [[Asia Minor]]. Eleven similar cases during the 1980s have been documented in [[Istanbul]], [[Turkey]].<ref name="Poison honey">{{cite journal |author1=Sütlüpmar, Nurhayat |author2=Mat, Afife |author3=Satganoglu, Yurdagül |name-list-style=amp |date=February 1993 |title=Poisoning by toxic honey in Turkey |journal=Archives of Toxicology |volume=67 |issue=2 |pages=148–150 |doi=10.1007/BF01973687 |pmid=8481104 |bibcode=1993ArTox..67..148S |s2cid=9658996}}</ref> 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. Rhododendron, including its stems, leaves and flowers, contains toxins that, if ingested by a cat's stomach, can cause seizures and even coma and death.<ref>{{Cite web |title=10 plants that are poisonous to cats |url=https://bombaykittens.com/catsblog/tpost/oppr98scs1-10-plants-that-are-poisonous-to-cats}}</ref>

==Uses==
''Rhododendron'' species have long been used in traditional medicine.<ref>{{cite journal | last1 = Popescu | first1 = R | last2 = Kopp | first2 = B | date = May 2013 | title = The genus Rhododendron: an ethnopharmacological and toxicological review | journal = J Ethnopharmacol | volume = 147 | issue = 1| pages = 42–62 | doi = 10.1016/j.jep.2013.02.022 | pmid = 23454683}}</ref><ref name="O'Neill_al2017">{{cite journal |last1=O'Neill |first1=A. R.|last2=Badola |first2=H.K. |last3=Dhyani |first3=P. P. |last4=Rana |first4=S. K. |date=2017 |title=Integrating ethnobiological knowledge into biodiversity conservation in the Eastern Himalayas |journal=Journal of Ethnobiology and Ethnomedicine |volume=13 |issue=1 |pages=21 |doi=10.1186/s13002-017-0148-9 |pmid=28356115 |pmc=5372287 |doi-access=free }}</ref> Animal studies and ''[[in vitro]]'' research have identified possible anti-inflammatory and hepatoprotective activities which may be due to the antioxidant effects of [[flavonoid]]s or other [[natural phenol|phenolic compound]]s and [[saponin]]s the plant contains.<ref name="aafr">{{cite journal | last = Agarwal | first = S.S. |author2=Sharma Kalpana | title = Anti-inflammatory activity of flowers of ''Rhododendron arboreum'' (SMITH) in rat's hind paw oedema induced by various phlogistic agents | journal = Indian Journal of Pharmacology | volume = 20 | issue = 2 | pages = 86–89 | year = 1988 | url = http://www.ijp-online.com/article.asp?issn=0253-7613;year=1988;volume=20;issue=2;spage=86;epage=89;aulast=Agarwal;type=0}}</ref> Xiong ''et al.'' have found that the root of the plant is able to reduce the activity of [[NF-κB]] in rats.<ref name="erra">{{cite journal | doi = 10.1016/S1007-4376(09)60031-9 | title = The effect of root of rhododendron on the activation of NF-κB in a chronic glomerulonephritis rat model |date=January 2009 | last1 = Xiong | first1 = Jing | last2 = Zhu | first2 = Zhonghua | last3 = Liu | first3 = Jianshe | last4 = Wang | first4 = Yang | journal = Journal of Nanjing Medical University | volume = 23 |issue=1 | pages = 73–78}}</ref>

In [[Nepal]], 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.<ref name="Regmi">{{cite book |last=Regmi |first=Puskal Prasad |url=https://books.google.com/books?id=9jo6AAAAMAAJ |title=An introduction to Nepalese food plants |date=1982 |publisher=Royal Nepal Academy}}</ref>{{rp|51}} The flower, fresh or dried, is added to fish curry in the belief that it will soften the bones.<ref name="Regmi" />{{rp|53}} The juice of rhododendron flower is used to make a [[Squash (drink)|squash]] called burans (named after the flower) in the hilly regions of [[Uttarakhand]]. It is admired for its distinctive flavor and color.<ref>{{cite book |last=Chauhan |first=Narain Singh |url=https://books.google.com/books?id=gAQnTAU-3lcC |title=Medicinal and Aromatic Plants of Himachal Pradesh |date=1999 |publisher=Indus Publishing |isbn=9788173870989 |page=355}}</ref>

=== Labrador tea ===
{{main|Labrador tea}}

The [[herbal tea]] called Labrador tea (not a true [[tea]]) is made from one of three closely related species: 
* ''[[Rhododendron tomentosum]]'' (Northern Labrador tea, previously ''[[Ledum palustre]]'')
* ''[[Rhododendron groenlandicum]]'', (Bog Labrador tea, previously ''[[Ledum groenlandicum]]'' or ''[[Ledum latifolium]]'')
* ''[[Rhododendron neoglandulosum]]'', (Western Labrador tea, or trapper's tea, previously ''[[Ledum glandulosum]]'')

==In culture==
In [[Uttarakhand]], in [[north India]], the Buransh flower is deeply embedded in local culture, playing a significant role in festivals like Holi and weddings, where it is used in garlands and decorations to bless attendees. The flower is also utilized in making a healthful, [[antioxidant]]-rich juice that is popular during local festivities and summer months. Additionally, Buransh flowers are incorporated into local arts and crafts, where they are used to make colorful necklaces and jewelry, symbolizing the spiritual and physical prosperity of the community.<ref>{{cite web |title=Uttarakhand ka rajya pushp: Buraansh |date=24 April 2024 |url=https://raebaar.com/uttarakhand-ka-rajya-pushp-buraansh/ |access-date=25 Apr 2024 |publisher=Raebaar.com}}</ref>

The rhododendron is the national flower of Nepal.[[File:Pink Rhododendron Blossom Prashar Himachal Apr11 P1020872.jpg|thumb|State flower of Himachal Pradesh]]
In the [[language of flowers]], the rhododendron symbolizes danger and to beware.<ref>{{Cite web |url=http://www.languageofflowers.com/flowermeaning.htm |title=Language of Flowers – Flower Meanings and Flower Sentiments |website=www.languageofflowers.com |access-date=26 November 2016 |archive-date=24 November 2016 |archive-url=https://web.archive.org/web/20161124141728/http://languageofflowers.com/flowermeaning.htm |url-status=dead }}</ref>

''[[Rhododendron arboreum]]'' (''lali guransh'') is the national flower of [[Nepal]]. ''R. ponticum'' is the [[Floral emblem|state flower]] of [[Jammu and Kashmir (state)|Indian-administered Kashmir]] and [[Azad Kashmir|Pakistan-controlled Kashmir]]. ''[[Rhododendron niveum]]'' is the state tree of [[Sikkim]] in [[India]]. <!-- this paragraph needs to be moved to the species when articles are created for them. The species for Sikkim is R. niveum, which is not more tree-like than other rhododendrons and is quite a bit less tree-like than R. arboreum, R. falconeri, or R. grande (all Sikkim natives). ''[[Dendrobium nobile]]'' is the Sikkim state flower. --> Rhododendron arboreum is also the state tree of the state of [[Uttarakhand]], India. Pink Rhododendron (''[[Rhododendron campanulatum]]'') is the state flower of [[Himachal Pradesh]], India. Rhododendron is also the provincial flower of Jiangxi, China and the state flower of [[Nagaland]], the 16th state of the Indian Union.

''[[Rhododendron maximum]]'', the most widespread rhododendron of the [[Appalachian Mountains]], is the state flower of the US state of [[West Virginia]], and is in the [[Flag of West Virginia]].

''[[Rhododendron macrophyllum]]'', a widespread rhododendron of the [[Pacific Northwest]], is the state flower of the US state of [[Washington (state)|Washington]].

Amongst the [[Zomi]] tribes in [[India]] and [[Myanmar]], "Rhododendrons" called "Ngeisok" is used in a poetic manner to signify a lady.{{citation needed|date=May 2016}}[[File:Leon Wyczółkowski - Różowe azalie.jpg|thumb|[[Leon Wyczółkowski]], ''Pink Rhododendrons'', 1903]]
===In media===
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".

Rhododendrons play a role and are soliloquized in [[James Joyce]]'s ''[[Ulysses (novel)|Ulysses]]''. The flowers are referenced throughout [[Daphne Du Maurier]]'s novel ''[[Rebecca (novel)|Rebecca]]'' (1938){{citation needed|date=May 2016}} and in [[Sharon Creech]]'s [[young adult]] novel ''[[Walk Two Moons]]'' (1994). British author [[Jasper Fforde]] also uses rhododendron as a motif throughout many of his books, e.g. the ''[[Thursday Next]]'' series<ref>{{Cite book | url = https://books.google.com/books?id=OaHIeqT1G9kC&q=jasper+fforde+%22rhododendron%22+thursday+next&pg=PT306 | title = Something rotten | isbn = 978-0-14-303541-1 | last1 = Fforde | first1 = Jasper | date = 26 July 2005| publisher = Penguin }}</ref> and ''[[Shades of Grey]]'' (2009).<ref>{{cite web|author=Jasper Fforde |url=http://www.jasperfforde.com/grey/interview.html |title=Shades of Grey – An Interview with Jasper Fforde about Shades of Grey |publisher=Jasperfforde.com |access-date=26 February 2013}}</ref>

The effects of ''R.&nbsp;ponticum'' were mentioned in the 2009 film ''[[Sherlock Holmes (2009 film)|Sherlock Holmes]]'' as a proposed way to arrange a [[fake execution]].<ref>{{cite web |author=Captain Skellett |date=27 December 2009 |title=Rhododendron poison – truth behind the science of Sherlock Holmes |url=http://www.aschoonerofscience.com/?p=932 |access-date=26 February 2013 |publisher=A Schooner of Science}}</ref> It was also mentioned in the third episode of Season&nbsp;2 of BBC's ''[[Sherlock (TV series)|Sherlock]]'', speculated to have been a part of Sherlock's fake death scheme.{{citation needed |date=June 2020}}

==See also==
* [[List of Award of Garden Merit rhododendrons]]
* [[List of Rhododendron diseases]]
* [[List of Rhododendron species]]
* [[List of Sections in Subgenus Rhododendron]]

==References==
{{Reflist|30em|refs=

<ref name=BH>{{cite book |author1-link=George Bentham |last1=Bentham |first1=G. |author2-link=Joseph Dalton Hooker |last2=Hooker |first2=J.D. |name-list-style=amp |title=Genera plantarum ad exemplaria imprimis in herbariis kewensibus servata definita. Vol. 2 Part II|year=1876|volume=2 |publisher=Reeve & Co.|location=London |url=https://www.biodiversitylibrary.org/item/14687#page/74/mode/1up |language=la |access-date=10 July 2014}}</ref>

<ref name=Chamberlain>{{cite book |url=http://www.rbge.org.uk/about-us/publications/publications-catalogue/botanical-publications/rhododendron-publications |last1=Chamberlain |first1=DF |last2=Hyam |first2=R |last3=Argent |first3=G |last4=Fairweather |first4=G |last5=Walter |first5=KS |date=1996 |title=The genus ''Rhododendron'': its classification and synonymy |publisher=Royal Botanic Garden Edinburgh |location=Edinburgh |isbn=978-1-872291-66-6 |archive-url=https://web.archive.org/web/20160304031738/http://www.rbge.org.uk/about-us/publications/publications-catalogue/botanical-publications/rhododendron-publications |archive-date=4 March 2016}}</ref>

<ref name=Cox1993>{{cite book |url=https://books.google.com/books?id=yp1FAAAAYAAJ |last=Cox |first=P.A. |title=The Cultivation of Rhododendrons |date=1993 |publisher=B.T. Batsford |location=London |pages=80–81 |isbn=978-0-7134-5630-1}}</ref>

<ref name=Don>{{cite book |url=https://www.biodiversitylibrary.org/item/9905#page/851/mode/1up |last=Don |first=G. |author-link=George Don |title=General History of Dichlamydious Plants |location=London |date=1834 |volume=iii |page=843|publisher=J.G. and F. Rivington}}</ref>

<ref name=Maximovicz>{{cite book |url=https://catalog.hathitrust.org/Record/011553641 |last=Maximowicz |first=C.J. |title=Rhododendreae Asiae Orientalis |trans-title=Rhododendreae East Asia |language=la |location=St. Pétersbourg |date=1870}}</ref>

<ref name=Sleumer66>{{cite book |chapter-url=https://www.biodiversitylibrary.org/item/90405#page/3/mode/1up |last=Sleumer |first=H |date=1966 |chapter=Ericaceae |title=Flora Malesiana. Series I, Spermatophyta (vol. 6 pt. 4) |url=https://www.biodiversitylibrary.org/bibliography/40744#/summary |editor=CGGJ van Steenis |pages=469–656 |publisher=Noordhoff-Kolff |location=Djakarta |doi=10.5962/bhl.title.40744}}</ref>

<ref name=Sleumer80>{{cite conference |last=Sleumer |first=H |date=1980 |title=Past and present taxonomic systems of ''Rhododendron'' based on macromorphological characters |book-title=Contributions Toward a Classification of Rhododendron: Proceedings of the International Rhododendron Conference |editor1-first=J.L. |editor1-last=Luteyn |editor2-first=M.E. |editor2-last=O'Brien |name-list-style=amp |pages=19–26 |publisher=New York Botanical Garden Press |location=New York |isbn=978-0-89327-221-0 |conference=International Rhododendron Conference (The New York Botanical Garden, 15–17 May 1978)}}</ref>

}}

==Bibliography==
===Books and book chapters===
* {{cite book |author=Augustin Pyramus de Candolle |year=1838 |title=Prodromus systemati naturalis regni vegetabilis sive enumeratio contracta ordinum, generum specierumque plantarum huc usque cognitarum, juxta methodi naturalis normas digesta |volume=7 |chapter-url=https://www.biodiversitylibrary.org/item/7156#page/724/mode/1up |chapter=Rhododendron |pages=719–728 |publisher=Treuttel et Würtz |location=Paris |language=la |ref=Candolle|author-link=Augustin Pyramus de Candolle}} (also available online at [http://gallica.bnf.fr/ Gallica])
* {{cite book |url=https://babel.hathitrust.org/cgi/pt?id=hvd.hn4xa9;view=1up;seq=7 |last=Sweet |first=Robert |title=The British Flower Garden |series=The Two Series |volume=I |author-link=Robert Sweet (botanist) |others=Drawings by E.D. Smith |publisher=James Ridgway & Sons |location=London |date=1838}}
* {{cite book |url=https://www.biodiversitylibrary.org/bibliography/11178#/summary |author-last=Hooker |author-first=Joseph Dalton |editor-last=Hooker |editor-first=William Jackson |title=The Rhododendrons of Sikkim-Himalaya: being an account, botanical and geographical, of the rhododendrons recently discovered in the mountains of eastern Himalaya, from drawings and descriptions made on the spot, during a government botanical mission to that country |publisher=Reeve, Benham, and Reeve |location=London |date=1849 |edition=2nd |doi=10.5962/bhl.title.11178}}
* {{cite conference |url=https://books.google.com/books?id=zbogAQAAIAAJ |editor1-first=James Leonard |editor1-last=Luteyn |editor2-first=Mary E. |editor2-last=O'Brien |name-list-style=amp |title=Contributions Toward a Classification of Rhododendron: Proceedings of the International Rhododendron Conference |conference=International Rhododendron Conference (The New York Botanical Garden, May 15–17, 1978) |publisher=New York Botanical Garden Press |location=New York |date=1980 |isbn=978-0-89327-221-0}}
* {{cite book |last=Davidian |first=H.H. |title=The Rhododendron Species |date=1982–1995 |publisher=Timber Press |location=Portland, Oregon |ref=Davidian}} In four volumes: Vol. I. ''Lepidotes'' {{ISBN|0-917304-71-3}}, Vol. II. ''Elepidotes. Arboreum-Lacteum'' {{ISBN|0-88192-109-2}}, Vol. III. ''Elepidotes Continued, Neriiflorum-Thomsonii, Azaleastrum and Camtschaticum'' {{ISBN|0-88192-168-8}}, Vol. IV. ''Azaleas'' {{ISBN|0-88192-311-7}}.
* {{cite book |url=https://books.google.com/books?id=yftGAAAAYAAJ |last1=Cox |first1=Peter A. |name-list-style=amp |last2=Cox |first2=Kenneth N. E. |title=The Encyclopedia of Rhododendron Species |date=1997 |publisher=Glendoick Publishing |isbn=978-0-9530533-0-8}}.
* {{cite book |url=https://archive.org/details/hardyrhododendro00cull_0 |url-access=registration |first=James |last=Cullen |title=Hardy Rhododendron Species: A Guide To Identification |publisher=Timber Press |date=2005 |isbn=978-0881927238 |ref=Cullen2005}}
* {{cite book |chapter-url=http://www.rhododendron.dk/rhododendron.pdf |author1-last=Blazich |author1-first=Frank A. |name-list-style=amp |author2-first=D. Bradley |author2-last=Rowe |date=July 2008 |chapter=''Rhododendron'' L., rhododendron and azalea |pages=943–951 |url=https://www.fs.fed.us/rm/pubs_series/wo/wo_ah727.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://www.fs.fed.us/rm/pubs_series/wo/wo_ah727.pdf |archive-date=2022-10-09 |url-status=live |editor1-first=Franklin T. |editor1-last=Bonner |editor2-first=Robert P. |editor2-last=Karrfalt |title=The Woody Plant Seed Manual |series=Agr. Hdbk |volume=727 |publisher=U.S. Dept. Agr. For. Serv. |location=Washington, D.C.}}

=== Articles ===
* {{cite journal |url=http://scholar.lib.vt.edu/ejournals/JARS/v23n4/v23n4-black.htm |first=Michael |last=Black |title=Historical Survey of Rhododendron Collecting With Emphasis on its Close Associations with Horticulture |journal=The Quarterly Bulletin of the American Rhododendron Society |volume=23 |issue=4 |date=October 1969}}
* {{cite journal |url=http://scholar.lib.vt.edu/ejournals/JARS/v44n4/v44n4-magor.htm |first=Walter |last=Magor |title=A History of Rhododendrons |journal=Journal American Rhododendron Society |volume=44 |issue=4 |date=Fall 1990}}
* {{cite journal |last1=Goetsch |first1=Loretta A.|last2=Eckert |first2=Andrew J. |last3=Hall |first3=Benjamin D. |date=July–September 2005 |title=The molecular systematics of ''Rhododendron'' (Ericaceae): a phylogeny based upon ''RPB2'' gene sequences |journal=[[Systematic Botany]] |volume=30 |issue=3 |pages=616–626 |doi=10.1600/0363644054782170 |bibcode=2005SysBo..30..616G |s2cid=51949019|ref=Goetsch}}

===Subdivisions===
[[Image:Dept Agriculture azaleas and rhododendrons publication.jpg|thumb|upright=0.67|right|The cultural requirements of azaleas and rhododendrons are so similar that this 1960 U.S. Department of Agriculture publication treated them together.]]

====Azaleas====
* {{cite book |url=https://www.biodiversitylibrary.org/item/116284#page/1/mode/1up |author-last1=Wilson |author-first1=E.H. |author-last2=Rehder |author-first2=A. |title=A Monograph of Azaleas; Rhododendron Subgenus Anthodendron |publisher=University Press |location=Cambridge |date=1921 |series=Publications of the Arnold Aboretum, no. 9}}
* {{cite journal |first=John L. |last=Creech |title=An Embryological Study in the ''Rhododendron'' Subgenus ''Anthodendron'' Endl. |journal=Botanical Gazette |volume=116 |issue=3 |date=1955 |pages=234–243 |jstor=2473343 |doi=10.1086/335866|s2cid=83861676 }}

====Tsutsusi====
* {{cite journal |last1=Chamberlain |first1=D.F. |last2=Rae |first2=S.J. |name-list-style=amp |year=1990 |title=A revision of ''Rhododendron''. IV. Subgenus ''Tsutsusi'' |journal=Edinburgh Journal of Botany |volume=47 |issue=2 |pages=89–200 |doi=10.1017/S096042860000319X |ref=ChamRae1990|doi-access=free }}
* {{cite conference |url=http://2004.botanyconference.org/engine/search/index.php?func=detail&aid=147 |author-last1=Powell |author-first1=E. Ann |author-last2=Kron |author-first2=Kathleen A |title=''"Molecular systematics of ''Rhododendron'' subgenus ''Tsutsusi'' (Rhodoreae, Ericoideae, Ericaceae)"'' |conference=Botany 2004 |conference-url=http://2004.botanyconference.org/ |date=2004 |id=Abstract ID:147}}
* {{cite journal |author-first1=K.A. |author-last1=Kron |name-list-style=amp |author-first2=E.A. |author-last2=Powell |title=Molecular systematics of ''Rhododendron'' subgenus ''Tsutsusi'' (Rhodoreae, Ericoideae, Ericaceae) |journal=Edinburgh Journal of Botany |volume=66 |issue=1 |date=March 2009 |pages=81–95 |doi=10.1017/S0960428609005071|doi-access=free }}
* {{cite journal |author1=ZHANG Yue-Jiao |author2=JIN Xiao-Feng |author3=DING Bing-Yang |author4=ZHU Jing-Ping |title=Pollen morphology of ''Rhododendron'' subgen. ''Tsutsusi'' and its systematic implications |journal=Journal of Systematics and Evolution |volume=47 |issue=2 |pages=123–138 |date=March 2009 |doi=10.1111/j.1759-6831.2009.00011.x|bibcode=2009JSyEv..47..123Z |s2cid=86594487}}
* {{cite journal |author1=JIN Xiao-Feng |author2=DING Bing-Yang |author3=ZHANG Yue-Jiao |author4=HONG De-Yuan |title=A Taxonomic Revision Of ''Rhododendron'' subg. ''Tsutsusi'' sect. ''Brachycalyx'' (Ericaceae) |journal=Annals of the Missouri Botanical Garden |volume=97 |issue=2 |pages=163–190 |date=2010 |doi=10.3417/2007139 |bibcode=2010AnMBG..97..163X |s2cid=86507576 |url=https://www.biodiversitylibrary.org/part/390541 |ref=JDZH}}

====Vireya====
* {{cite book |last=Sleumer |first=Hermann Otto |title=An account of rhododendron in Malesia |publisher=P. Noordhoff |location=Groningen |date=1966}}. A reprint from Flora Malesiana ser. I, vol. 6, part 4. Pages 473 through 674. 
* {{cite journal |url=http://scholar.lib.vt.edu/ejournals/JARS/v32n1/v32n1-leach.htm |first=David G. |last=Leach |title=The Discovery of the Malaysian Rhododendrons |journal=The Quarterly Bulletin of the American Rhododendron Society |volume=32 |issue=1 |date=Winter 1978}}
* {{cite book |last=Argent |first=G. |title=Rhododendrons of subgenus Vireya |date=2006 |publisher=Royal Horticultural Society |isbn=978-1-902896-61-8 |ref=Argent2006}}
* {{cite journal | url = https://www.researchgate.net/publication/235601539 | last1 = Brown | first1 = Gillian K. | last2 = Craven | first2 = Lyn A. | last3 = Udovicic | first3 = Frank | last4 = Ladiges | first4 = Pauline Y. |date=August 2006 | title = Phylogenetic relationships of ''Rhododendron'' section ''Vireya'' (Ericaceae) inferred from the ITS nrDNA region | journal = Australian Systematic Botany | volume = 19 | issue = 4| pages = 329–342 | doi = 10.1071/SB05019 | bibcode = 2006AuSyB..19..329B |ref=Brown2006 |archive-date=15 July 2014 |archive-url=https://web.archive.org/web/20140715012754/http://www.researchgate.net/profile/Frank_Udovicic/publication/235601539_Phylogenetic_relationships_of_Rhododendron_section_Vireya_(Ericaceae)_inferred_from_the_ITS_nrDNA_region/file/72e7e51e347034a1c1.pdf}}
* {{cite journal |last1=Hall |first1=B.D. |first2=L.A. |last2=Craven |name-list-style=amp |first3=L.A. |last3=Goetsch |date=2006 |title=The Taxonomy of Subsection ''Pseudovireya'': Two distinctly different taxa within subsection ''Pseudovireya'' and their Relation to the Rooting of section ''Vireya'' within subgenus ''Rhododendron'' |journal=Rhododendron Species |volume=1 |pages=91–97}} Yearbook of the Rhododendron Species Foundation, Federal Way, WA.
* {{cite journal | doi = 10.3767/000651908X608070 | title = Classification of the ''Vireya'' group of ''Rhododendron'' (Ericaceae) | year = 2008 | last1 = Craven | first1 = L.A. | last2 = Goetsch | first2 = L.A. | last3 = Hall | first3 = B.D. | last4 = Brown | first4 = G.K. | journal = Blumea - Biodiversity, Evolution and Biogeography of Plants | volume = 53 | issue = 2 | pages = 435–442 | bibcode = 2008Blume..53..435C |ref=Craven2008| url = http://www.repository.naturalis.nl/record/525519}}
* {{cite journal |last1=Goetsch |first1=L.A. |last2=Craven |first2=L.A. |last3=Hall |first3=B.D. |year=2011 |title=Major speciation accompanied the dispersal of Vireya Rhododendrons (Ericaceae, ''Rhododendron'' sect. ''Schistanthe'') through the Malayan archipelago: Evidence from nuclear gene sequences |journal=Taxon |volume=60 |issue=4 |pages=1015–1028|doi=10.1002/tax.604006|bibcode=2011Taxon..60.1015G }}
* {{Cite journal |url=http://www.whitecloudnursery.com/Vireya%20Phylogeny%20pt%20I.pdf |author-first=Peter |author-last=Adams |title=Evolution, Adaptive Radiation and Vireya Rhododendrons - Part I |journal=Journal American Rhododendron Society |date=Fall 2012 |pages=201–203 |access-date=18 June 2014 |archive-url=https://web.archive.org/web/20160820032816/http://www.whitecloudnursery.com/Vireya%20Phylogeny%20pt%20I.pdf |archive-date=20 August 2016 |url-status=dead}}
* {{Cite journal |url=http://www.whitecloudnursery.com/Vireya%20Phylogeny%20pt%20II.pdf |author-first=Peter |author-last=Adams |title=Evolution, Adaptive Radiation and Vireya Rhododendrons – Part II |journal=Journal American Rhododendron Society |date=Spring 2013 |pages=74–76 |access-date=18 June 2014 |archive-url=https://web.archive.org/web/20160820034157/http://www.whitecloudnursery.com/Vireya%20Phylogeny%20pt%20II.pdf |archive-date=20 August 2016 |url-status=dead}}
* {{cite thesis |url=https://mro.massey.ac.nz/handle/10179/4468 |title=Biodiversity of the Vireya group of Rhododendron L. (Ericaceae) collections in New Zealand and their potential contribution to international conservation |last=Fayaz |first=A. |type=PhD |publisher=Massey University |location=Turitea, New Zealand |date=2012 |ref=Fayaz |access-date=26 September 2017}}

====Separate genera====
* {{cite journal |last=Craven |first=L.A. |title=''Diplarche'' and ''Menziesia'' transferred to ''Rhododendron'' (''Ericaceae'') |journal=Blumea - Biodiversity, Evolution and Biogeography of Plants |volume=56 |issue=1 |date=April 2011 |pages=33–35 |doi=10.3767/000651911X568594 |bibcode=2011Blume..56...33C |url=https://repository.naturalis.nl/pub/525706 |ref=Craven2011}}

==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==
{{Commons category|Rhododendron}}
{{Wikispecies}}
{{Wiktionary}}

* [http://www.rhodyman.net/rhodyhis.html History of Rhododendron Discovery & Culture]
* [https://web.archive.org/web/20090606220644/http://www.lahana.org/blog/Rhododendrons.htm Rhododendrons from Turkey, Anatolia]
* [http://www.rhododendron.dk/alfabet.html Danish Genebank Rhododendron]
* [http://www.rhododendron.dk/arter-lande.html Danish Genebank. Rhododendron in different countries]
* [http://www.lwk-niedersachsen.de/index.cfm/action/rhodo.html?lang=gb German Genebank Rhododendron] {{Webarchive|url=https://web.archive.org/web/20120315181800/http://www.lwk-niedersachsen.de/index.cfm/action/rhodo.html?lang=gb |date=15 March 2012 }}
* [http://www.countrysideinfo.co.uk/rhododen.htm Description of damage caused by Rhododendrons in the UK]
* [http://www.wfu.edu/~kronka/kakbek/rhododendrons.html Information on rhododendrons at the Ericaceae web pages of Dr. Kron at Wake Forest University.]
* [http://www.vireya.net/ Information on Vireyas]
* [https://web.archive.org/web/20181215224227/http://www.hirsutum.info/ Information+photos of hybrids and species]
* [http://www.rhodophiles.com/ Information on Rhododendrons by Marc Colombel, founder of the Société Bretonne du Rhododendron.]
* [http://rhodyman.net/rahome.html Extensive information on rhododendron species: the history of their discovery, botanical details, toxicity, classification, cultural conditions, care for common problems, and suggestions for companion plants by Steve Henning.]
* [https://web.archive.org/web/20090130005655/http://www.rhodo.citymax.com/page/page/627471.htm History of Rhododendrons]
* [http://www.rododendron.cz/fotogalerie-rododendronu/pruhonicky-park-2011/ Rhododendron in botanical garden Pruhonice-Czech republic ] {{Webarchive|url=https://web.archive.org/web/20171007024344/http://www.rododendron.cz/fotogalerie-rododendronu/pruhonicky-park-2011/ |date=7 October 2017 }}

===Databases===
* [[USDA]] Plants Database: [http://plants.usda.gov/core/profile?symbol=RHODO ''Rhododendron'']
* [[ITIS]] Report: [https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=23700 ''Rhododendron'']
* [http://www.efloras.org/index.aspx ''eFloras.org'']
** [http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=128386 Flora of North America: Rhododendron]
** [http://www.efloras.org/florataxon.aspx?flora_id=2&taxon_id=128386 Flora of China: Rhododendron]
** [http://www.efloras.org/florataxon.aspx?flora_id=110&taxon_id=128386 Annotated Checklist of the Flowering Plants of Nepal: Rhododendron]

===Societies===
* [http://rhododendron.org/ American Rhododendron Society]
** [http://scholar.lib.vt.edu/ejournals/JARS/#qbars The Quarterly Bulletin of the American Rhododendron Society 1947–1981]
** [http://scholar.lib.vt.edu/ejournals/JARS/#jars Journal of the American Rhododendron Society (JARS) 1982–]
** {{cite web|url=http://www.rhododendron.org/taxonomictree.asp|title=Genus Rhododendron Taxonomic Tree|work=American Rhododendron Society|ref=ARS2}} Information Source: {{cite book |first1=Peter A. |last1=Cox |name-list-style=amp |first2=Kenneth N. E. |last2=Cox |title=The Encyclopedia of Rhododendron Species |publisher=Glendoick Publishing |date=1997 |isbn=978-0-9530533-0-8}}.
* [http://www.rhodogroup-rhs.org/ The Rhododendron, Camellia & Magnolia Group of the Royal Horticultural Society]
* [http://www.rhodygarden.org/ Rhododendron Species Foundation and Botanical Garden]
* [https://web.archive.org/web/20060408075911/http://honeybee.helsinki.fi/users/avainola/rhodo/club.htm Société Finlandaise du Rhododendron]
* [http://www.rhododendron.com.au Australian Rhododendron Society]
* [https://web.archive.org/web/20151105130749/http://www.rhodo.org/start.php?lang=gb German Rhododendron Society]
* [http://www.rhododendron.org.nz/ New Zealand Rhododendron Association]
* [http://www.rhododendron.dk/ Danish Rhododendron Society]
* [http://frasersouthrhodos.ca/ Fraser South Rhododendron Society]

===Botanical gardens===
* [http://www.rbge.org.uk/the-gardens/rhododendrons Royal Botanic Garden Edinburgh: Rhododendrons at the four Gardens] {{Webarchive|url=https://web.archive.org/web/20180529031923/http://www.rbge.org.uk/the-gardens/rhododendrons |date=29 May 2018 }}
* [http://parkweb.vic.gov.au/explore/parks/national-rhododendron-garden National Rhododendron Gardens Melbourne Australia]

{{Rhododendron}}
{{Taxonbar|from=Q189393}}
{{Authority control}}

[[Category:Rhododendron| ]]
[[Category:Ericaceae genera]]
[[Category:Plants used in traditional Chinese medicine]]
[[Category:National symbols of Nepal]]
[[Category:Neurotoxins]]
[[Category:Taxa named by Carl Linnaeus]]
[[Category:Extant Ypresian first appearances]]