Editing Rhododendron (section)

===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}}