Editing Dahlia (section)

=== Subdivision ===

====Infrageneric subdivision ====
{{See also|List of Dahlia species}}
Sherff (1955), in the first modern taxonomy described three sections for the 18 species he recognised, ''Pseudodendron'', ''Epiphytum'' and ''Dahlia''.<ref>Sherff, E. E. 1955. Dahlia. Compositae-Heliantheae-Coreopsidinae. [[North American Flora]]. Part 2:45–59. [[New York Botanical Garden]]</ref> By 1969 Sørensen recognised 29 species and four sections by splitting off ''Entemophyllon'' from section ''Dahlia''.<ref name=Sorensen69>{{cite journal | last1 = Sørensen | first1 = P. D. | year = 1969 | title = Revision of the genus Dahlia (Compositae, Heliantheae-Coreopsidinae) | url = https://archive.org/stream/mobot31753003413934/mobot31753003413934_djvu.txt | journal = Rhodora | volume = 71 | issue = 309–365| pages = 367–416 }}</ref> By contrast Giannasi (1975) using a [[phytochemical]] analysis based on [[flavonoids]], reduced the genus to just two sections, ''Entemophyllon'' and ''Dahlia'', the latter having three subsections, ''Pseudodendron'', ''Dahlia'', and ''Merckii''.<ref>David E Giannasi. The flavonoid systematics of the genus Dahlia (comstoopidpositae). ''Memoirs of the New York Botanical Garden'', 26,2. New York Botanical Garden, 1975.</ref> Sørensen then issued a further revision in 1980, incorporating subsection ''Merckii'' in his original section ''Dahlia''.<ref>{{cite journal | last1 = Sørensen | first1 = P. D. | year = 1980 | title = New taxa in the genus Dahlia (Asteraceae, Heliantheae-Coreopsidinae) | url = https://archive.org/stream/mobot31753003488282/mobot31753003488282_djvu.txt | journal = Rhodora | volume = 82 | pages = 353–360 }}</ref>
When he described two new species in the 1980s (''[[Dahlia tubulata]]'' and ''[[Dahlia congestifolia|D.&nbsp;congestifolia]]''), he placed them within his existing sections.<ref>{{cite journal | last1 = Sørensen | first1 = P. D. | year = 1987 | title = Dahlia congestifolia, Section Entemophyllon (Asteraceae: Heliantheae, Coreopsidinae), new from Hidalgo, Mexico | journal = Rhodora | volume = 89 | pages = 197–203 }}</ref> A further species, ''[[Dahlia sorensenii]]'' was added by Hansen and Hjerting in (1996).<ref>{{cite journal | last1 = Hansen | first1 = H. V. | last2 = Hierting | first2 = J. P. | year = 1996 | title = Observations on chromosome numbers and biosystematics in Dahlia (Asteraceae, Heliantheae) with an account on the identity of D. pinnata, D. rosea and D. coccinea | journal = Nordic Journal of Botany | volume = 16 | issue = 4| pages = 445–455 | doi=10.1111/j.1756-1051.1996.tb00256.x}}</ref> 
At the same time they demonstrated that ''[[Dahlia pinnata]]'' should more properly be designated ''D.&nbsp;x pinnata''. ''D.&nbsp;x pinnata'' was shown to actually be a variant of ''D.&nbsp;sorensenii'' that had acquired hybrid qualities before it was introduced to Europe in the sixteenth century and formally named by Cavanilles.<ref name=Cavanilles>{{cite book |last= Cavanilles |first= A. J. |author-link= |year= 1791 |title= Icones et Descriptiones Plantarum |url= https://www.loc.gov/resource/gdcwdl.wdl_15013_001/?sp=138&st=image&r=0.084,0.648,1.24,0.607,0 |location= Madrid, Spain |volume= 1 |page=57 |via= [[Library of Congress]]}}</ref> The original wild ''D.&nbsp;pinnata'' is presumed extinct. Further species continue to be described, Saar (2003) describing 35 species.<ref name=Saar/> However separation of the sections on morphological, cytologal and biocemical criteria has not been entirely satisfactory.<ref name=Saar/>

To date these sectional divisions have not been fully supported [[phylogenetically]],<ref name="Kamenetsky">{{cite book |url=https://books.google.com/books?id=5B-ucdbgA3wC |title=Ornamental Geophytes: From Basic Science to Sustainable Production |publisher=CRC Press |year=2012 |isbn=978-1-4398-4924-8 |editor-last1=Kamenetsky |editor-first1=Rina |location=Boca Raton, Florida, USA |editor-last2=Okubo |editor-first2=Hiroshi}}</ref> which demonstrate only section ''Entemophyllon'' as a distinct sectional [[clade]]. The other major grouping is the core ''Dahlia'' clade (CDC), which includes most of the section ''Dahlia''. The remainder of the species occupy what has been described as the variable root clade (VRC) which includes the small section ''Pseudodendron'' but also the monotypic section ''Epiphytum'' and a number of species from within section ''Dahlia''. Outside of these three clades lie ''D.&nbsp;tubulata'' and ''D.&nbsp;merckii'' as a [[polytomy]].<ref name=Saar/>

Horticulturally the sections retain some usage, section ''Pseudodendron'' being referred to as 'Tree Dahlias', ''Epiphytum'' as the 'Vine Dahlia'. The remaining two herbaceous sections being distinguished by their [[pinnules]], opposing (''Dahlia'') or alternating (''Entemophyllon'').<ref>[http://www.dahlia-nds.co.uk/about_dahlias/Specie_Dahlia.htm National Dahlia Society: Dahlia species]</ref>

===== Sections =====
Sections (including [[chromosome numbers]]), with geographical distribution;<ref>{{cite journal | last1 = Hansen | first1 = H. V. | year = 2004 | title = Simplified keys to four sections with 34 species in the genus Dahlia (Asteraceae-Coreopsideae) | journal = Nordic Journal of Botany | volume = 24 | issue = 5| pages = 549–553 | doi = 10.1111/j.1756-1051.2004.tb01639.x }}</ref>
* ''Epiphytum'' Sherff (2n = 32)
**10 m tall climber with aerial roots 5&nbsp;cm thick and up to more than 20 m long; pinnules opposite
** 1 species, ''D.&nbsp;macdougallii'' Sherff 
** Mexico: Oaxaca
* ''Entemophyllon'' P. D. Sorensen (2n = 34)
** 6 species
** Mexico: Hidalgo, Nuevo León, Tamaulipas, Querétaro, Durango, San Luis Potosí 
* ''Pseudodendron'' P. D. Sorensen (2n = 32)
** 3 species + ''D.&nbsp;excelsa'' of uncertain identity
** Mexico: Chiapas, Guerrero, Jalisco, Michoacan, Oaxaca, and Costa Rica, El Salvador, Guatemala & Colombia
*  ''Dahlia'' (2n = 32, 36 or 64)
** 24 species
** Mexico: Distrito Federal, Guerrero, Hidalgo, Morelos, Nuevo León, Puebla, San Luis Potosí, Tamaulipas, Veracruz, Oaxaca, Puebla, Chiapas, México, Huehuetenango, Chihuahua, Durango, Michoacan & Guatemala

Only ''Pseudodendron'' (''[[Dahlia imperialis|D.&nbsp;imperialis]]'') and ''Dahlia'' (''D.&nbsp;australis'', ''D.&nbsp;coccinea'') occur outside Mexico.

=====Species=====
{{main|List of Dahlia species}}
There are currently 42 accepted species in the genus ''Dahlia''<ref>{{cite web |title=Dahlia |url=http://www.theplantlist.org/1.1/browse/A/Compositae/Dahlia/ |website=The Plant List |archive-url=https://web.archive.org/web/20190413220709/http://www.theplantlist.org/1.1/browse/A/Compositae/Dahlia/ |archive-date=13 April 2019}}</ref> but new species continue to be described.<ref name=Kamenetsky/>