Editing Rhododendron (section)

===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}}