View source for Dahlia

{{Short description|Genus of flowering plants in the daisy family Asteraceae}}
{{Other uses}}
{{distinguish|text=[[Dalea]], in family Fabaceae}}
{{Automatic taxobox
| image = Dahlia_x_hybrida.jpg
| image_caption = Dahlia flower
| display_parents = 2
| taxon = Dahlia
| authority = [[Antonio José Cavanilles|Cav.]]<ref name=Cavanilles/>
| type_species = ''[[Dahlia pinnata]]''
| type_species_authority = Cav.<ref name=Cavanilles/>
| synonyms =
*''Georgina'' <small>[[Carl Ludwig Willdenow|Willd.]]</small>
*''Georgia'' <small>[[Kurt Polycarp Joachim Sprengel|Spreng.]]</small>
| synonyms_ref = <ref name = "POWO, 2023">{{cite POWO |id=325940-2 |title=''Dahlia'' Cav. |accessdate=21 July 2023}}</ref>
| subdivision_ranks = [[Section (botany)|Sections]]
| subdivision =
* ''Dahlia''
* ''Entemophyllon''
* ''Epiphytum''
* ''Pseudodendron''
}}
'''''Dahlia''''' ({{IPAc-en|uk|ˈ|d|eɪ|l|i|ə}} {{respell|DAY|lee|ə}}, {{IPAc-en|us|ˈ|d|æ|l|j|ə|,_|ˈ|d|ɑː|l|j|ə|,_|ˈ|d|eɪ|l|j|ə}} {{respell|DA(H)L|yə|,_|DAYL|yə}})<ref>{{cite book
|title=Longman pronunciation dictionary
|first=John C.
|last= Wells
|publisher=Longman
|location=Harlow, England
|year=1990
|isbn=978-0582053830
}} entry "Dahlia"
</ref> is a [[genus]] of bushy, [[Root tuber|tuberous]], [[herbaceous]] [[perennial]] plants native to Mexico and Central America. Dahlias are members of the [[Asteraceae]] (synonym name: Compositae) family of [[dicotyledon]]ous plants,<ref name="WFO">{{cite web |url=http://www.worldfloraonline.org/taxon/wfo-4000010667 |title= ''Dahlia'' Cav. Icon. 1: 56 (t. 80) (1791) |date= 2022 |website= World Flora Online |publisher= World Flora Consortium |access-date= 30 November 2022}}</ref> its relatives include the [[sunflower]], [[Bellis perennis|daisy]], [[chrysanthemum]], and [[zinnia]]. There are 49 [[species]] of dahlia,<ref name="WFO" /> with flowers in almost every hue (except blue), with [[Hybrid (biology)|hybrid]]s commonly grown as garden plants.
Dahlias were known only to the [[Aztecs]] and other southern North American peoples until the [[Spanish conquest of the Aztec Empire|Spanish conquest]], after which the plants were brought to Europe. The tubers of some varieties are of medicinal and dietary value to humans because they contain [[inulin]], a polymer of the fruit sugar, [[fructose]].
== Description ==
{{multiple image
| perrow = 2
| total_width = 300
| align =
| direction =
| width =
| image1 = Dahlia Blooming.jpg
| caption1 =
| image2 = Dahlia Blooming Bud.jpg
| caption2 =
| image3 = Dahlia Almost Bloomed (2).jpg
| image4 = Dahlia flower buds 1.jpg
| image5 = Dahlia flower plant.jpg
| image6 = Dahlia flower buds 2.jpg
| footer = '''''Complete Stages of Dahlia Flower:''''' (start from 2nd row 1st pic clockwise) Complete Bloomed Flower, Blooming Bud. Bud, Bud in The tree And Dahlia Plant; Captured In [[National Institute of Technology Agartala|NIT Agartala]], [[India]]
}}
Dahlias are perennial plants with tuberous roots. They are not frost hardy, and require protection from frost if grown in regions with cold winters. While some have herbaceous stems, others have stems which lignify in the absence of secondary tissue and resprout following winter dormancy, allowing further seasons of growth.<ref name=Saar/> As members of the family [[Asteraceae]], dahlias have composite flower heads called [[Pseudanthium|capitula]] that are composed of multiple [[floret]]s arranged in a central disc with surrounding petal-like rays. Each floret is a flower in its own right. The modern name Asteraceae comes from the type genus ''[[Aster (genus)|Aster]]'' and the [[Ancient Greek]] word for "star", referring to the appearance of a star with surrounding rays.
The stems are leafy, ranging in height from as low as {{convert|12|in|cm|abbr=off|order=flip}} to more than {{convert|6|-|8|ft|m|abbr=off|order=flip}}. Flower forms are variable, with one head per stem; these can be as small as {{convert|2|in|cm|abbr=on|0|order=flip}} in diameter or up to {{convert|1|ft|cm|abbr=on|order=flip}} ("dinner plate"). The majority of species do not produce scented flowers. Like most plants that do not attract [[pollination|pollinating]] insects through scent, they are brightly colored, displaying most hues, with the exception of blue.
The great variety in species results from garden dahlias being [[octoploid]]s, having eight sets of [[Sequence homology|homologous]] [[chromosome]]s. In addition, dahlias also contain many [[transposons]]—genetic pieces that move from place to place upon an [[allele]]—which contributes to their manifesting such great diversity.
== Taxonomy==
=== Taxonomic history ===
==== Early history ====
{{multiple image
| align             = right
| total_width       = 320
| image1            = Flowers 107.jpg
| alt1              = Dahlia
| caption1          = Dahlia
| image2            = Orange Dahlia01.jpg
| alt2              = Orange Dahlia
| caption2          = Orange Dahlia
| footer            =
| image3            =
| caption3          = Blue Dahlia
| alt3              = Blue Dahlia
}}
Spaniards reported finding the plants growing in Mexico in 1525, but the earliest known description is by [[Francisco Hernández de Toledo|Francisco Hernández]], physician to [[Philip II of Spain|Philip II]], who was ordered to visit Mexico in 1570 to study the "natural products of that country". They were used as a source of food by the indigenous peoples, who both gathered wild specimens and cultivated crops.<ref name=":0">[http://arnoldia.arboretum.harvard.edu/pdf/articles/1705.pdf Harvard Arboretum]</ref><ref name="autogenerated2002">Katz, Solomon H.; Weaver, William Woys Weaver, Encyclopedia of Food and Culture, The Gale Group, New York, 2002.</ref> The indigenous peoples variously identified the plants as "Chichipatl" ([[Toltecs]]) and "Acocotle" or "Cocoxochitl" ([[Aztecs]]). From Hernandez's perception of [[Nahuatl]] to [[Spanish language|Spanish]] (through various other translations) the word is "water cane", "water pipe", "water pipe flower", "hollow stem flower", or "cane flower", all referring to the hollow plant stems.<ref>Safford, W.E., "Notes on Dahlias", Journal of the Washington Academy of Sciences, 1919.</ref>
Hernandez described two varieties of dahlias (the pinwheel-like ''[[Dahlia pinnata]]'' and the huge ''Dahlia imperialis'') as well as other medicinal plants of New Spain. Francisco Dominguez, an Hidalgo gentleman who accompanied Hernandez on part of his seven-year study, made a series of drawings to supplement the four volume report. Three of his drawings showed plants with flowers: two resembled the modern bedding dahlia, and one resembled the species ''[[Dahlia merckii]]''; all displayed a high degree of doubleness.<ref>Hernandez, Francisco, Nova Plantarum Animalum et Mineralium Historia. Pg. 31-32,372. 1651.</ref> In 1578, a manuscript titled ''Nova Plantarum, Animalium et Mineralium Mexicanorum Historia'', was sent back to the [[Escorial]] in Madrid.<ref>Hernández, ''Rerum medicarum Novae Hispaniae thesaurus'' (Rome, 1651); details of the introduction of the dahlia to European gardens are taken from {{Harvtxt|Harshberger|1897}}</ref> It was translated into Latin by Francisco Ximenes in 1615. In 1640, Francisco Cesi, President of the ''Academia dei Lincei'' of Rome, bought the Ximenes translation and, after annotating it, published it in 1649–1651 as two volumes, ''Rerum Medicarum Novae Hispaniae Thesaurus Seu Nova Plantarium, Animalium et Mineralium Mexicanorum Historia''. The original manuscripts were destroyed in a fire in the mid-1600s.<ref>{{cite journal | last1 = Baltet | first1 = Charles | year = 1906 | title = Comment le Dahlia est arrive du Mexique en Europe | journal = Revue Horticole | volume = 78 | pages = 209–212 }}</ref>
====European introduction====
{{multiple image
| align = right
| total_width = 320
| image1 = Scarlet-flowered dahlia.jpg
| alt1 = Dahlia coccinea
| caption1 = ''Dahlia coccinea'', parent of European "single" dahlias (i.e., displaying a single row of ligulate florets)
| image2 = Dahlia sambucifolia 1805.png
| alt2 = Dahlia sambucifolia
| caption2 = ''Dahlia sambucifolia''
| footer =
}}
In 1787, the French botanist [[Nicolas-Joseph Thiéry de Menonville]], sent to Mexico to steal the [[cochineal]] insect valued for its scarlet dye, reported the strangely beautiful flowers he had seen growing in a garden in Oaxaca.<ref>Menonville, ''Traité de la culture du nopal et de l'education de la cochenille dans les colonies françaises de l'Amérique'' 1787.</ref> In 1789, [[Vicente Cervantes]], director of the Botanical Garden at Mexico City, sent "plant parts" to Abbe [[Antonio José Cavanilles]], director of the [[Real Jardín Botánico de Madrid|Royal Gardens of Madrid]].<ref>From the director, Sr. Vicentes Cervantes, according to Augustin Legrand and Pierre-Denis Pépin, ''Manuel du cultivateur de dahlias'', "Introduction en Europe", Paris, 1848, p. 10.</ref> Cavanilles flowered one plant that same year, then the second one a year later. In 1791 he called the new growths "Dahlia" for [[Anders Dahl]].<ref name=Cavanilles/> The first plant was called ''Dahlia pinnata'' after its [[pinnate]] foliage; the second, ''Dahlia rosea'' for its rose-purple color. In 1796, from the parts sent by Cervantes, Cavanilles flowered a third plant, which he named ''[[Dahlia coccinea]]'' for its scarlet color.
In 1798, Cavanilles sent ''D.&nbsp;pinnata'' seeds to [[Parma]], Italy. That year, the Marchioness of Bute, wife of [[John Stuart, 1st Marquess of Bute|the Earl of Bute]], the English Ambassador to Spain, obtained a few seeds from Cavanilles and sent them to [[Kew Gardens]], where they flowered but were lost after two to three years.<ref name="autogenerated5">Dean, Richard, The dahlia: its history and cultivation, Macmillan, 1897, p.5.</ref>
[[File:Holland House in 1907 by J. Benjamin Stone - Dahlia Garden.jpg|thumb|right|The Dahlia Garden at Holland House in 1907]]
In the following years Madrid sent seeds to Berlin and Dresden in Germany, and to Turin and Thiene in Italy. In 1802, Cavanilles sent tubers of "these three" (''D.&nbsp;pinnata, D.&nbsp;rosea, D.&nbsp;coccinea'') to Swiss botanist [[Augustin Pyramus de Candolle]] at University of Montpelier in France, [[Andre Thouin]] at the [[Jardin des Plantes]] in Paris and Scottish botanist [[William Aiton]] at Kew Gardens.{{sfn|Weland|2015|loc=p.&nbsp;8}} That same year, John Fraser, English nurseryman and later botanical collector to the Czar of Russia, brought ''[[D. coccinea|D.&nbsp;coccinea]]'' seeds from Paris to the [[Chelsea Physic Garden|Apothecaries Gardens]] in England, where they flowered in his greenhouse a year later, providing ''Botanical Magazine'' with an illustration.
In 1804, a new species, ''Dahlia sambucifolia'', was successfully grown at [[Holland House, London|Holland House]], Kensington. Whilst in Madrid in 1804, [[Elizabeth Fox, Baroness Holland|Lady Holland]] was given either dahlia seeds or tubers by Cavanilles.<ref>{{cite book|last=Forbes|first=James|author2=John Russell Bedford|title=Hortus woburnensis|publisher=J. Ridgway|year=1833|page=[https://archive.org/details/hortuswoburnens00forbgoog/page/n282 246]|url=https://archive.org/details/hortuswoburnens00forbgoog}}</ref> She sent them back to England, to Lord Holland's librarian at Holland House, who successfully raised the plants<ref>{{cite book|last=Hogg|first=Robert|author-link=Robert Hogg (biologist)|title=The Dahlia; Its History and Cultivation|publisher=Groombidge and Sons|year=1853|page=[https://archive.org/details/dahliaitshistor00hogggoog/page/n34 5]|url=https://archive.org/details/dahliaitshistor00hogggoog}}</ref><ref>{{cite journal|journal=Transactions of the Horticultural Society of London|date=1808-04-05|volume=1|page=93|location=London|publisher=W. Bulmer & Co.|title=Observations on the different Species of Dahlia, and the best Method of Cultivating them in Britain.|last=Salisbury|first=R. A.}}</ref> and produced two double flowers a year later.{{sfn|Weland|2015|loc=p.&nbsp;2}} The plants raised in 1804 did not survive; new stock was brought from France in 1815.<ref name="autogenerated5"/> In 1824, Lord Holland sent his wife a note containing the following verse:<blockquote>The dahlia you brought to our isle<br />
Your praises for ever shall speak;<br />
Mid gardens as sweet as your smile,<br />
And in colour as bright as your cheek.<ref>{{cite book|last=Ward|first=Bobby J.|title=A Contemplation Upon Flowers|publisher=Timber Press|year=1999|page=119|url=https://books.google.com/books?id=n3MgSchHBjYC|isbn=978-0-88192-469-5}}
</ref></blockquote>
In 1805, German naturalist [[Alexander von Humboldt]] sent more seeds from Mexico to Aiton in England, Thouin in Paris, and [[Christoph Friedrich Otto]], director of the [[Berlin Botanical Garden]]. More significantly, he sent seeds to botanist [[Carl Ludwig Willdenow]] in Germany. Willdenow now reclassified the rapidly growing number of species, changing the genus from ''Dahlia'' to ''Georgina''; after naturalist [[Johann Gottlieb Georgi]]. He combined the Cavanilles species ''D.&nbsp;pinnata'' and ''D.&nbsp;rosea'' under the name of ''Georgina variabilis''; ''D.&nbsp;coccinea'' was still held to be a separate species, which he renamed ''Georgina coccinea''.
===Classification===
[[File:Close up of a Dahlia x cultorum Thorsrud & Reisaeter.jpg|thumb|Close up of a Dahlia x cultorum Thorsrud & Reisaeter in [[Piracicaba]], Brazil]]
Since 1789 when Cavanilles first flowered the dahlia in Europe, there has been an ongoing effort by many growers, botanists and taxonomists, to determine the development of the dahlia to modern times. At least 85 species have been reported: approximately 25 of these were first reported from the wild; the remainder appeared in gardens in Europe. They were considered [[hybrid (biology)|hybrid]]s, the results of crossing between previously reported species, or developed from the seeds sent by Humboldt from Mexico in 1805, or perhaps from some other undocumented seeds that had found their way to Europe. Several of these were soon discovered to be identical with earlier reported species, but the greatest number are new varieties. [[Morphological variation]] is highly pronounced in the dahlia. [[William John Cooper Lawrence]], who hybridized hundreds of families of dahlias in the 1920s, stated: "I have not yet seen any two plants in the families I have raised which were not to be distinguished one from the other.<ref>Lawrence, W.J.C. "The Genetics and Cytologogy of Dahlia variabilis", ''Journal of Genetics'', July 24, 1931, p. 257.</ref> Constant reclassification of the 85 reported species has resulted in a considerably smaller number of distinct species, as there is a great deal of disagreement today between systematists over classification.{{sfn|Weland|2015|loc=p.&nbsp;13}}
In 1829, all species growing in Europe were reclassified under an all-encompassing name of ''D.&nbsp;variabilis, Desf.'', though this is not an accepted name.{{sfn|Bates|2015|loc=[http://www.dahliaworld.co.uk/dahlia.htm Dahlia types and international classification of dahlias]}} Through the interspecies cross of the Humboldt seeds and the Cavanilles species, 22 new species were reported by that year, all of which had been classified in different ways by several different taxonomists, creating considerable confusion as to which species was which. As of now Dahlias are classified into 15 different species by botanist [[Liberty Hyde Bailey]].<ref>{{Cite web |title=Stanford Dahlia Project Dahlia Hybridization History |url=https://web.stanford.edu/group/dahlia_genetics/dahlia_history.htm |access-date=2023-12-12 |website=web.stanford.edu}}</ref>
In 1830 William Smith suggested that all dahlia species could be divided into two groups for color, red-tinged and purple-tinged. In investigating this idea Lawrence determined that with the exception of ''D.&nbsp;variabilis'', all dahlia species may be assigned to one of two groups for flower-colour: Group I (ivory-magenta) or Group II (yellow-orange-scarlet).{{citation needed|date=September 2020}}
=== Modern classification ===
The genus ''Dahlia'' is situated in the [[Asteroideae]] [[subfamily]] of the [[Asteraceae]], in the [[Coreopsideae]] [[Tribe (biology)|tribe]]. Within that tribe it is the second largest genus, after ''Coreopsis'',<ref name=Saar/> and appears as a well defined [[clade]] within the Coreopsideae.<ref>{{citation | title = Phylogeny of Coreopsideae (Asteraceae) using ITS sequences suggests lability in reproductive characters | author = Rebecca T. Kimballa, Daniel J. Crawford | journal = Molecular Phylogenetics and Evolution | volume = 33 | year = 2004 | pages = 127–139 | doi = 10.1016/j.ympev.2004.04.022 | pmid = 15324843 | issue = 1 | bibcode = 2004MolPE..33..127K }}</ref>
=== 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/>
===Etymology===
The naming of the plant itself has long been a subject of some confusion. Many sources state that the name "Dahlia" was bestowed by the pioneering Swedish botanist and taxonomist [[Carl Linnaeus]] to honor his late student, [[Anders Dahl]], author of ''Observationes Botanicae''. However, Linnaeus died in 1778, more than eleven years before the plant was introduced into Europe in 1789, so while it is generally agreed that the plant was named in 1791 in honor of Dahl, who had died two years before,<ref>Stafleu, F. A.; Cowan, R.S., Taxonomic literature, vol. 1: A–G, Utrecht, 1976.</ref> Linnaeus could not have been the one who did so. It was probably Abbe [[Antonio Jose Cavanilles]], Director of the Royal Gardens of Madrid, who should be credited with the attempt to scientifically define the genus, since he not only received the first specimens from Mexico in 1789, but named the first three species that flowered from the cuttings.{{sfn|Weland|2015|loc=p.&nbsp;2}}
Regardless of who bestowed it, the name was not so easily established. In 1805, German botanist [[Carl Ludwig Willdenow]], asserting that the genus ''Dahlia'' Thunb. (published a year after Cavanilles's genus and now considered a synonym of ''[[Trichocladus]]'') was more widely accepted, changed the plants' genus from ''Dahlia'' to ''Georgina'' (after the [[Germany|German]]-born naturalist [[Johann Gottlieb Georgi]], a professor at the Imperial Academy of Sciences of [[St. Petersburg]], [[Russia]]).<ref>Willdenow. Species Plantarum. Ed. 4. vol. 3. pt. 3. pp. 2124-2125. 1800.[https://www.biodiversitylibrary.org/item/14564#page/650/mode/1up]</ref> He also reclassified and renamed the first three species grown, and identified, by Cavanilles. It was not until 1810, in a published article, that he officially adopted the Cavanilles's original designation of ''Dahlia''.<ref>Willdenow von, The Dahlia, Enumeratio Plantarum. Hor. Reg. Bot. Berolinensis, 899, 1809.</ref> However, the name ''Georgina'' still persisted in Germany for the next few decades. In Russian, it is still named Georgina ({{langx|ru|георгинa}}).
== Distribution and habitat ==
''Dahlia'' is found predominantly in [[Mexico]], but some species are found ranging as far south as northern [[South America]].<ref name=Kamenetsky/> ''[[Dahlia australis|D.&nbsp;australis]]'' occurs at least as far south as southwestern [[Guatemala]], while ''D.&nbsp;coccinea'' and ''D.&nbsp;imperialis'' also occur in parts of [[Central America]] and northern South America. ''Dahlia'' is a genus of the uplands and mountains, being found at elevations between {{Convert|1,500 and 3,700|m|abbr=on}}, in what has been described as a "pine-oak woodland" [[vegetative zone]]. Most species have limited ranges scattered throughout many mountain ranges in Mexico <ref name=Saar/>
== Ecology ==
The most common pollinators are bees and small beetles.<ref name=Saar/>
===Pests and diseases===
{{more citations needed section|date=October 2022}}
{{main|List of Dahlia diseases}}
[[Slugs]] and [[snails]] are serious pests in some parts of the world, particularly in spring when new growth is emerging through the soil. [[Earwigs]] can also disfigure the blooms and foliage.<ref>{{Cite web |last=Nash |first=Kim Ruddock-last modified by June |title=Pests & Diseases |url=https://www.dahlia-nds.co.uk/about-dahlias/pests-diseases/ |access-date=2024-05-22 |website=National Dahlia Society |language=en-GB}}</ref> The other main pests likely to be encountered are [[aphids]] (usually on young stems and immature flower buds), [[red spider mite]] (causing foliage mottling and discolouration, worse in hot and dry conditions) and [[capsid bug]]s (resulting in contortion and holes at growing tips).<ref>{{Cite web |last=Jaros |first=Liz |date=2022-04-19 |title=11 Dahlia Pests: How to Identify, Prevent, and Treat Them |url=https://www.epicgardening.com/dahlia-pests/ |access-date=2024-05-22 |website=Epic Gardening |language=en-US}}</ref> Diseases affecting dahlias include [[powdery mildew]],<ref>{{Cite web|title=Dahlia (group) - Plant Finder|url=https://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?taxonid=264590&isprofile=1&basic=dahlia|access-date=2021-10-03|website=www.missouribotanicalgarden.org}}</ref> grey mould (''[[Botrytis cinerea]]''), [[verticillium]] wilt, dahlia [[smut (fungus)|smut]] (''Entyloma calendulae'' f. ''dahliae''), [[phytophthora]] and some [[plant viruses]]. Dahlias are a source of food for the [[larva]]e of some [[Lepidoptera]] species including [[angle shades]], [[common swift (moth)|common swift]], [[ghost moth]] and [[large yellow underwing]].
==Cultivation==
Dahlias grow naturally in climates that do not experience frost (the tubers are hardy to [[USDA Zone]] 8), consequently they are not adapted to withstand sub-zero temperatures. However, their tuberous nature enables them to survive periods of [[dormancy]], and this characteristic means that gardeners in temperate climates with frosts can grow dahlias successfully, provided the tubers are lifted from the ground and stored in cool yet frost-free conditions during the winter. Planting the tubers quite deep ({{Convert|10–15|cm|abbr=on|disp=or|frac=2}}) also provides some protection. When in active growth, modern dahlia hybrids perform most successfully in well-watered yet free-draining soils, in situations receiving plenty of sunlight. Taller cultivars usually require some form of staking as they grow, and all garden dahlias need [[Deadheading (flowers)|deadheading]] regularly, once flowering commences.<ref>{{cite web|url=https://www.gardenersworld.com/how-to/grow-plants/how-to-grow-dahlias/|title=How to Grow Dalias|publisher= BBC- Gardners World|access-date=1 February 2023}}</ref>
=== Horticultural classification ===
Horticulturally the garden dahlia is usually treated as the [[cultigen]] ''D.&nbsp;variabilis'' [[hort.]], which while being responsible for thousands of cultivars has an obscure taxonomic status.<ref name="Kamenetsky" />{{rp|41–42}}
==== History ====
The inappropriate term ''D.&nbsp;variabilis'' is often used to describe the cultivars of ''Dahlia'' since the correct parentage remains obscure, but probably involves ''[[Dahlia coccinea]]''.<ref name=Saar/>{{sfn|Bates|2015|loc=[http://www.dahliaworld.co.uk/dahlia.htm Dahlia types and international classification of dahlias]}} In 1846 the Caledonia Horticultural Society of [[Edinburgh]] offered a prize of 2,000 pounds to the first person succeeding in producing a blue dahlia.<ref>Wuyts, O.F., "Le Dahlia", Ledeberg-Gana Belgium, 1926.</ref> This has to date not been accomplished. While dahlias produce [[anthocyanin]], an element necessary for the production of the blue, to achieve a true blue color in a plant, the anthocyanin [[delphinidin]] needs six [[hydroxyl]] groups. To date, dahlias have only developed five, so the closest that breeders have come to achieving a "blue" specimen are variations of mauve, purples and lilac hues.<ref>Dietz, Deborah. (ed.), "Dahlia Genetics: Whence and Whither?", ''Dahlia Society of America Newsletter'', July 2009.</ref>
By the beginning of the twentieth century, a number of different types were recognised. These terms were based on shape or colour, and the National Dahlia Society included cactus, pompon, single, show and fancy in its 1904 guide. Many national societies developed their own classification systems until 1962 when the International Horticultural Congress agreed to develop an internationally recognised system at its Brussels meeting that year, and subsequently in Maryland in 1966. This culminated in the 1969 publication of ''The International Register of Dahlia Names'' by the Royal Horticultural Society which became the central registering authority.{{sfn|Bates|2015|loc=[http://www.dahliaworld.co.uk/dahlia.htm Dahlia types and international classification of dahlias]}}
This system depended primarily on the visibility of the central disc, whether it was open-centred or whether only ray florets were apparent centrally (double bloom). The double-bloom cultivars were then subdivided according to the way in which they were folded along their longitudinal axis: flat, involute (curled inwards) or revolute (curling backwards). If the end of the ray floret was split, they were considered fimbriated. Based on these characteristics, nine groups were defined plus a tenth miscellaneous group for any cultivars not fitting the above characteristics.{{sfn|RHS|2015|loc=[https://www.rhs.org.uk/plants/pdfs/Plant-register-supplements/Dahlias/13th-Dahlia-Supplement The International Dahlia Register 1969. Thirteenth Supplement (2002)]}} Fimbriated dahlias were added in 2004,{{sfn|RHS|2015|loc=[https://www.rhs.org.uk/plants/pdfs/Plant-register-supplements/Dahlias/15th-Dahlia-Supplement The International Dahlia Register 1969. Fifteenth Supplement (2004)]}} and two further groups (Single and Double orchid) in 2007.{{sfn|RHS|2015|loc=[https://www.rhs.org.uk/plants/pdfs/Plant-register-supplements/Dahlias/18th-Dahlia-Supplement The International Dahlia Register 1969. Eighteenth Supplement (2007)]}} The last group to be added, Peony, first appeared in 2012.{{sfn|RHS|2015|loc=[https://www.rhs.org.uk/plants/pdfs/Plant-register-supplements/Dahlias/22nd-Dahlia-Supplement The International Dahlia Register 1969. Twenty Second Supplement (2012)]}}
In many cases the bloom diameter was then used to further label certain groups from miniature to giant.{{sfn|Bates|2015|loc=[http://www.dahliaworld.co.uk/dahlia.htm Dahlia types and international classification of dahlias]}} This practice was abandoned in 2012.{{sfn|RHS|2015|loc=[https://www.rhs.org.uk/plants/pdfs/Plant-register-supplements/Dahlias/22nd-Dahlia-Supplement The International Dahlia Register 1969. Twenty Second Supplement (2012)]}}
==== Modern system (RHS) ====
There are now more than 57,000 registered [[cultivars]],{{sfn|Bates|2015|loc=[http://www.dahliaworld.co.uk/encyclo.htm Dahlia Encyclopaedia]}}
which are officially registered through the [[Royal Horticultural Society]] (RHS).{{sfn|RHS|2015|loc=[https://www.rhs.org.uk/plants/plantsmanship/plant-registration/Dahlia-cultivar-registration Dahlia cultivar registration]}} The official register is ''The International Register of Dahlia Names 1969'' (1995 reprint) which is updated by annual supplements. The original 1969 registry published about 14,000 cultivars adding a further 1700 by 1986 and in 2003 there were 18,000.{{sfn|Bates|2015|loc=[http://www.dahliaworld.co.uk/dahlia.htm Dahlia types and international classification of dahlias]}} Since then about a hundred new cultivars are added annually.{{sfn|RHS|2015|loc=[https://www.rhs.org.uk/plants/plantsmanship/plant-registration/Dahlia-cultivar-registration/Dahlia Dahlia publications]}}
{{see also|List of Dahlia cultivars}}
;Flower type
The official RHS classification lists fourteen groups, grouped by flower type, together with the abbreviations used by the RHS;{{sfn|RHS|2015|loc=[https://www.rhs.org.uk/plants/pdfs/Plant-register-supplements/Dahlias/24th-dahlia-supplement The International Dahlia Register (1969) Twenty-fourth Supplement 2014]}}{{sfn|Bates|2015|loc=[http://www.dahliaworld.co.uk/encyclo.htm Dahlia Encyclopaedia]}}{{sfn|NDS|2011|loc=[http://www.dahlia-nds.co.uk/about_dahlias/Dahlia_Classification.htm Dahlia Classification and Formation]}}
{{Dividing line}}
{{columns-list|colwidth=30em|
{{No col break|
* '''Group 1 – Single-flowered dahlias''' (''Sin'') – Flower has a central disc with a single outer ring of florets (which may overlap) encircling it, and which may be rounded or pointed.
**(e.g. 'Twyning's After Eight'{{sfn|RHS|2015|loc=[https://www.rhs.org.uk/Plants/219157/Dahlia-Twyning-s-After-Eight-%28Sin%29/Details ''Dahlia'' 'Twyning's After Eight' (Sin)]}})
<gallery>
File:TWYNINGS AFTER EIGHT.jpg|'Twyning's After Eight' (''Single'')
File:HS WINKweb.jpg|Dahlia "Happy Single Wink" (''Single'')
</gallery>
{{Dividing line}}}}
{{No col break|
* '''Group 2 – Anemone-flowered dahlias''' (''Anem'') – The centre of the flower consists of dense elongated tubular florets, longer than the disc florets of Single dahlias, while the outer parts have one or more rings of flatter ray florets. Disc absent.
**(e.g. 'Boogie Woogie'{{sfn|Dave's Garden|2015|loc=[http://davesgarden.com/guides/pf/go/62361/ Anemone Flowered Dahlia ''Dahlia'' 'Boogie Woogie']}})
<gallery>
File:Dahlia 'Boogie Woogie'.jpg|'Boogie Woogie' (''Anemone'')
File:COMETweb.jpg|Dahlia "Comet" (''Anemone'')
</gallery>
{{Dividing line}}}}
{{No col break|
* '''Group 3 – Collerette dahlias''' (''Col'') – Large flat florets forming a single outer ring around a central disc and which may overlap a smaller circle of florets closer to the centre, which have the appearance of a collar.{{sfn|Bates|2015|loc=[http://www.dahlias.co.uk/dahlia_types/collerette_dahlias.php Collarette Dahlias]}}
**(e.g. 'Starsister',<ref>[http://www.vanmeuwen.com/flowers/flower-plants/patio-plants/dahlia-star-sister-red-and-yellow/V52768VM Van Meuwen: ''Dahlia'' 'Star Sister']</ref> 'Lilian Alice', 'Apple Blossom')
<gallery>
File:Collarette Dahlia - "Apple Blossom" cultivar.jpg| 'Apple Blossom' (''Collerette'')
File:FASHION MONGERweb.jpg| 'Fashion Monger' (''Collerette'')
</gallery>
{{Dividing line}}}}
{{No col break|
* '''Group 4 – Waterlily dahlias''' (''WL'') – Double blooms, broad sparse curved, slightly curved or flat florets and very shallow in depth compared with other dahlias. Depth less than half the diameter of the bloom.
**(e.g. 'Cameo'{{sfn|Dave's Garden|2015|loc=[http://davesgarden.com/guides/pf/go/127958/ Waterlily Dahlia ''Dahlia''  'Cameo']}})
<gallery>
File:Dahlia - "Cameo" cultivar.jpg|'Cameo' (''Waterlily'')
File:BRACKENRIDGE BALLERINAweb.jpg|'Brackenridge Ballerina' (''Waterlily'')
</gallery>
{{Dividing line}}}}
{{No col break|
* '''Group 5 – Decorative dahlias''' (''D'') – Double blooms, ray florets broad, flat, involute no more than seventy five per cent of the longitudinal axis, slightly twisted and usually bluntly pointed. No visible central disc.{{sfn|Bates|2015|loc=[http://www.dahlias.co.uk/dahlia_types/decorative_dahlias.php Decorative Dahlias]}}
**(e.g. 'Berliner Kleene'{{sfn|Dave's Garden|2015|loc=[http://davesgarden.com/guides/pf/go/127287/Border Dahlia, Decorative Dahlia ''Dahlia''  'Berliner Kleene']}})
<gallery>
File:Dahlia 'Berliner Kleene'.jpg|'Berliner Kleene' (''Decorative'')
File:CAFE AU LAIT web.jpg|'Cafe au lait'  (''Decorative'')
File:Dahlia Woodland Merinda.jpg|'Woodland Merinda' (''Decorative'')
File:DAVID HOWARDweb.jpg|Dahlia 'David Howard' (''Decorative'')
</gallery>
{{Dividing line}}}}
{{No col break|
* '''Group 6 – Ball dahlias''' (''Ba'') – Double blooms that are ball shaped or slightly flattened. Ray florets blunt or rounded at the tips, margins arranged spirally, involute for at least seventy five percent of the length of the florets. Larger than Pompons.
**(e.g. 'Barbarry Ball'{{sfn|Dave's Garden|2015|loc=[http://davesgarden.com/guides/pf/go/133888/Ball Dahlia ''Dahlia''  'Barbarry Ball']}})
<gallery>
File:BARBARRYBALL.jpg|'Barbarry Ball' (''Ball'')
File:MARY'S JOMANDAweb.jpg|Dahlia "Mary's Jomanda" (''Ball'')
</gallery>
{{Dividing line}}}}
{{No col break|
* '''Group 7 – Pompon dahlias''' (''Pom'') – Double spherical miniature flowers made up entirely from florets that are curved inwards (involute) for their entire length (longitudinal axis), resembling a [[pompon]].
**(e.g. 'Small World'{{sfn|RHS|2015|loc=[https://www.rhs.org.uk/Plants/66966/i-Dahlia-i-Small-World-%28Pom%29/Details ''Dahlia'' 'Small World' (Pom)]}})
<gallery>
File:Dahlia - "Small World" cultivar.jpg|'Small World' (''Pompon'')
File:FRANZ KAFKAweb.jpg|Dahlia 'Franz Kafka' (''Large Pompon'')
</gallery>
{{Dividing line}}}}
{{No col break|
* '''Group 8 – Cactus dahlias''' (''C'') – Double blooms, ray florets pointed, with majority [[wikt:revolute|revolute]] (rolled) over more than fifty percent of their longitudinal axis, and straight or incurved. Narrower than Semi cactus.
**(e.g.  'Nuit d'Eté'{{sfn|Dave's Garden|2015|loc=[http://davesgarden.com/guides/pf/go/95672/ Cactus Dahlia ''Dahlia'' 'Nuit D'Ete']}})
<gallery>
File:Dahlia 'Nuit d'Eté'.jpg|'Nuit d'Eté' (''Cactus'')
File:Dahlia karmasangria.jpg|'Karma Sangria' (''Cactus'' cultivar)
File:JALDECJOKER.jpg|'Jaldec Joker' (small ''Cactus'')
File:ALFRED GRILLEweb.jpg|Dahlia 'Alfred Grille' (''Cactus'')
</gallery>
{{Dividing line}}}}
{{No col break|
* '''Group 9 – Semi cactus dahlias''' (''S–c'') – Double blooms, very pointed ray florets, revolute for greater than twenty five percent and less than fifty percent of their longitudinal axis. Broad at the base and straight or incurved, almost spiky in appearance.
**(e.g. 'Mick's Peppermint'{{sfn|Dave's Garden|2015|loc=[http://davesgarden.com/guides/pf/go/133874/ Semi-Cactus Dahlia ''Dahlia'' 'Mick's Peppermint']}})
<gallery>
File:MICKS PEPPERMINTweb.jpg|Dahlia 'Mick's Peppermint' (''Semi-cactus'')
File:3265 ALOHA (BRIDGE VIEW).jpg|Dahlia 'Bridge view aloha' (''Semi-cactus'')
</gallery>
{{Dividing line}}}}
{{No col break|
* '''Group 10 – Miscellaneous dahlias''' (''Misc'') –  not described in any other group.
**(e.g. [[Dahlia 'Akita'|'Akita']])
<gallery>
File:AKITAweb.jpg|Dahlia 'Akita' (''Miscellaneous'')
File:RAGGED ROBINweb.jpg| 'Ragged Robin' (''Miscellaneous'')
</gallery>
{{Dividing line}}}}
{{No col break|
* '''Group 11 – Fimbriated dahlias''' (''Fim'') – ray florets evenly split or notched into two or more divisions, uniformly throughout the bloom, creating a [[fimbriated]] (fringed) effect. The petals may be flat, involute, revolute, straight, incurving or twisted.
**(e.g. 'Marlene Joy'{{sfn|RHS|2015|loc=[https://www.rhs.org.uk/Plants/109241/Dahlia-Marlene-Joy-%28Fim%29/Details ''Dahlia'' 'Marlene Joy' (Fim)]}})
<gallery>
File:MARLENE JOYweb.jpg|'Marlene Joy' (''Fimbriated'')
File:NARGOLDweb.jpg|'Nargold' (''Fimbriated'')
</gallery>
{{Dividing line}}}}
{{No col break|
* '''Group 12 – Single Orchid (Star) dahlias''' (''SinO'') – single outer ring of florets surround a central disc. The ray florets are either involute or revolute.
**(e.g. 'Marie Schnugg')
<gallery>
File:MARIE SCHNUGGweb.jpg|'Marie Schnugg' (''Single orchid (Star)'')
File:HONKA FRAGILEweb.jpg|'Honka Fragile' (''Single orchid (Star)'')</gallery>
{{Dividing line}}}}
{{No col break|
* '''Group 13 – Double Orchid dahlias''' (''DblO'') – Double blooms with triangular centres. The ray florets are narrowly lanceolate and are either involute or revolute. The central disc is absent.
**(e.g. 'Pink Giraffe'{{sfn|National Dahlia Collection|2015|loc=[http://www.dahliaworld.co.uk/douborch.htm Double Orchid Dahlias. Pink Giraffe]}}{{sfn|RHS|2015|loc=[https://www.rhs.org.uk/Plants/53441/i-Dahlia-i-Pink-Giraffe-%28DblO%29/Details ''Dahlia'' 'Pink Giraffe' (DblO)]}})
<gallery>
File:Dahlia - "Pink Giraffe" cultivar.jpg|'Pink Giraffe' (''Double Orchid'')
File:JULIE ONEweb.jpg|Dahlia "Julie one" (''Double Orchid'')
</gallery>
{{Dividing line}}}}
{{No col break|
* '''Group 14 – Peony-flowered dahlias''' (''P'') – Large flowers with three or four rows of rays that are flattened and expanded and arranged irregularly. The rays surround a golden disc similar to that of Single dahlias.
**(e.g. [[Dahlia 'Bishop of Llandaff'|'Bishop of Llandaff']]{{sfn|RHS|2015|loc=[https://www.rhs.org.uk/plants/details?plantid=621 ''Dahlia'' 'Bishop of Llandaff' (P)]}})
<gallery>
File:DahliaLlandaff.jpg|'[[Dahlia 'Bishop of Llandaff'|'Bishop of Llandaff' (''Peony'')]]
File:FASCINATIONweb.jpg|Dahlia "Fascination" (''Peony'')
</gallery>
{{Dividing line}}}}
}}
;Flower size
Earlier versions of the registry subdivided some groups by flower size. Groups 4, 5, 8 and 9 were divided into five subgroups (A to E) from Giant to Miniature, and Group 6 into two subgroups, Small and Miniature. Dahlias were then described by Group and Subgroup, e.g. 5(d) ‘Ace Summer Sunset’.{{sfn|RHS|2015|loc=[https://www.rhs.org.uk/plants/pdfs/Plant-register-supplements/Dahlias/13th-Dahlia-Supplement The International Dahlia Register 1969. Thirteenth Supplement (2002)]}} Some Dahlia Societies have continued this practice, but this is neither official nor standardised. As of 2013 The RHS uses two size descriptors{{sfn|RHS|2015|loc=[https://www.rhs.org.uk/plants/pdfs/Plant-register-supplements/Dahlias/24th-dahlia-supplement The International Dahlia Register 1969. Twenty-fourth Supplement (2014)]}}
* '''Dwarf Bedder (Dw.B.)''' – not usually exceeding {{convert|600|mm|in|abbr=on}} in height, e.g. 'Preston Park' (''Sin/DwB''){{sfn|RHS|2015|loc=[https://www.rhs.org.uk/Plants/66186/i-Dahlia-i-Preston-Park-%28Sin-DwB%29/Details ''Dahlia'' 'Preston Park' (Sin/DwB)]}}
* '''Lilliput dahlias (Lil)''' – not usually exceeding {{convert|300|mm|in|abbr=on}} in height, with single, semi-double or double florets up to {{convert|26|mm|in|abbr=on}} in diameter. ("baby" or "top-mix" dahlias), e.g. 'Harvest Tiny Tot' (''Misc/Lil''){{sfn|RHS|2015|loc=[https://www.rhs.org.uk/Plants/116490/Dahlia-Harvest-Tiny-Tot-(Misc-Lil)/Details ''Dahlia'' 'Harvest Tiny Tot' (Misc/Lil)                            ]}}
Sizes can range from tiny micro dahlias with flowers less than 50''&nbsp;''mm to giants that are over 250''&nbsp;''mm in diameter. The groupings listed here are from the New Zealand Society:{{sfn|NDSNZ|2015|loc=[http://www.nzdahliasociety.50megs.com/varieties.html Dahlia varieties]}}
* '''Giant-flowered cultivars''' have blooms with a diameter over 250&nbsp;mm.
* '''Large-flowered cultivars''' have blooms with a diameter of 200–250&nbsp;mm.
* '''Medium-flowered cultivars''' have blooms with a diameter of 155–350&nbsp;mm.
* '''Small-flowered cultivars''' have blooms with a diameter of 115–155&nbsp;mm.
* '''Miniature-flowered cultivars''' have blooms with a diameter of 50–115&nbsp;mm.
* '''Pompom-flowered cultivars''' have blooms with a diameter less than 50&nbsp;mm.
In addition to the official classification and the terminology used by various dahlia societies, individual horticulturalists use a wide range of other descriptions, such as 'Incurved' and abbreviations in their catalogues, such as CO for Collarette.{{sfn|Linda's Dahlias|2015|loc=[http://www.lindasdahlias.com/Form___Size_Description.html#BloomType Bloom Type]}}
==== Branding ====
[[File:Dahlia 'Carolina Burgundy'.JPG|thumb|Dahlinova 'Carolina Burgundy' (''Misc'')]]
Some plant growers include their brand name in the cultivar name. Thus Fides{{sfn|Fides|2015}} (part of the Dümmen Orange Group{{sfn|Dümmen Orange|2015}}) in the Netherlands developed a series of cultivars which they named the Dahlinova series,{{sfn|Dahlinova|2008}} for example Dahlinova 'Carolina Burgundy'.{{sfn|Dahlinova|2008|loc=[http://dahlinova.com/product-range-dahlinova/carolina-burgundy.html Carolina Burgundy]}} These are Group 10 Miscellaneous in the RHS classification scheme.{{sfn|RHS|2015|loc=[http://apps.rhs.org.uk/planttrials/TrialReports/Dahlia2004.pdf Trials Report 2004. Dahlia. Miscellaneous Dahlinova Series]}}
===Double dahlias===
In 1805, several new species were reported with red, purple, lilac, and pale yellow coloring, and the first true double flower was produced in Belgium. One of the more popular concepts of dahlia history, and the basis for many different interpretations and confusion, is that all the original discoveries were single-flowered types, which, through hybridization and selective breeding, produced double forms.{{sfn|Weland|2015|loc=pp.&nbsp;4–5}} Many of the species of dahlias then, and now, have single-flowered blooms. ''D.&nbsp;coccinea'', the third dahlia to bloom in Europe, was a single. But two of the three drawings of dahlias by Dominguez, made in Mexico between 1570 and 1577, showed definite characteristics of doubling. In the early days of the dahlia in Europe, the word "double" simply designated flowers with more than one row of petals. The greatest effort was now directed to developing improved types of double dahlias.
During the years 1805 to 1810 several people claimed to have produced a double dahlia. In 1805 Henry C. Andrews made a drawing of such a plant in the collection of Lady Holland, grown from seedlings sent that year from Madrid.<ref>Andrews, Henry C., Botanist's Repository Vol. III, Plate 483, 1805.</ref> Like other doubles of the time it did not resemble the doubles of today. The first modern double, or full double, appeared in Belgium; M. Donckelaar, Director of the Botanic Garden at [[Leuven|Louvain]], selected plants for that characteristic, and within a few years secured three fully double forms.<ref>Wuyts, O. F., Le Dahlia. Ledeberg-Gana, Belgium. 1926.</ref> By 1826 double varieties were being grown almost exclusively, and there was very little interest in the single forms. Up to this time all the so-called double dahlias had been purple, or tinged with purple, and it was doubted if a variety untinged with that color was obtainable.
In 1843, scented single forms of dahlias were first reported in Neu Verbass, Austria.<ref>Michigan Special Bulletin #266. Ag. Exp. Sta., Mich. State College, 1935.</ref> ''D.&nbsp;crocea'', a fragrant variety grown from one of the Humboldt seeds, was probably interbred with the single ''D.&nbsp;coccinea''. A new scented species would not be introduced until the next century when the ''D.&nbsp;coronata'' was brought from Mexico to Germany in 1907.<ref>Anonymous, "A Scented Dahlia", ''Garden Chronicles'', 3rd Ser. 43, 1908, p. 128.</ref>
The exact date the dahlia was introduced in the United States is uncertain. One of the first dahlias in the USA may have been the ''D.&nbsp;coccinea speciosissima'' grown by William Leathe, of Cambridgeport, near Boston, around 1929. According to Edward Sayers,<ref>{{cite book | last = Sayers | first = Edward | year = 1839 | title = A treatise on the culture of the dahlia and cactus | doi = 10.5962/bhl.title.35596 | doi-access = free | page = 14 | url = https://www.biodiversitylibrary.org/bibliography/35596 | publisher = Weeks, Jordan and company | hdl = 2027/loc.ark:/13960/t77s8647h | hdl-access = free }}</ref> "it attracted much admiration, and at that time was considered a very elegant flower, it was however soon eclipsed by that splendid scarlet, the Countess of Liverpool". However, nine cultivars were already listed in the catalog from Thornburn, 1825.<ref>A G. Thorburn & Son. Catalogue of kitchen garden, herb, tree, flower, and grass seeds, bulbous flower roots, &c. &c. &c., 1825, p49, {{doi|10.5962/bhl.title.79195}}{{free access}}</ref> And even earlier reference can be found in a catalogue from the Linnaean Botanical Garden, New York, 1820, that includes one scarlet, one purple, and two double orange Dahlias for sale.<ref>Catalogue of Bulbous and Fibrous Rooted Plants, Cultivated and For Sale at the Linnaean Botanic Garden, Flushing, Long Island, near New York. 1820, {{doi|10.5962/bhl.title.68584}}{{free access}}</ref>
Sayers stated that "No person has done more for the introduction and advancement of the culture of
the Dahlia than George C. Thorburn, of New York, who yearly flowers many thousand plants at his place at Hallet's Cove, near Harlaem.{{Clarify|date=May 2021|reason=maybe Harlem?}}{{Citation needed|date=May 2021}} The show there in the flowering season is a rich treat for the lovers of floriculture : for almost every variety can be seen growing in two large blocks or masses which lead from the road to the dwelling-house, and form a complete field of the Dahlia as a foreground to the house. Mr. T. Hogg, William Read, and many other well-known florists have also contributed much in the vicinity of New York, to the introduction of the Dahlia. Indeed so general has become the taste that almost every garden has its show of the Dahlia in the season." In Boston too there were many collections, a collection from the Messrs Hovey of Cambridgeport was also mentioned.{{Citation needed|date=May 2021}}
In 1835 Thomas Bridgeman, published a list of 160 double dahlias in his "Florist's Guide".<ref>Thomas Bridgeman, "Florists' guide..., 1835, p.48–56, {{doi|10.5962/bhl.title.69431}}{{free access}}</ref> 60 of the choicest were supplied by Mr. G. C. Thornburn of Astoria, New York, who got most of them from contacts in the UK. Not a few of them had taken prizes "at the English and American exhibitions".{{Citation needed|date=May 2021}}
==="Stars of the Devil"===
In 1872 J. T. van der Berg of Utrecht in the Netherlands received a shipment of seeds and plants from a friend in Mexico. The entire shipment was badly rotted and appeared to be ruined, but van der Berg examined it carefully and found a small piece of root that seemed alive. He planted and carefully tended it; it grew into a plant that he identified as a dahlia. He made cuttings from the plant during the winter of 1872–1873. This was an entirely different type of flower, with rich, red color and a high degree of doubling. In 1874 van der Berg catalogued it for sale, calling it ''Dahlia juarezii'' to honor Mexican President [[Benito Pablo Juarez]], who had died the year before, and described it as "...equal to the beautiful color of the red poppy. Its form is very outstanding and different in every respect of all known dahlia flowers."<ref>van der Berg, J. T., "Dahlia juarezii", ''Gardeners Chronicle'', 1879.</ref>
This plant has perhaps had a greater influence on the popularity of the modern dahlia than any other. Called "Les Etoiles du Diable" (Stars of the Devil)<ref>"Die Dahlien. Ihre Geschichte, Kultur and Verwendung", ''German Dahlia Society'', Ch. VIII, 1926.</ref> in France and "Cactus dahlia" elsewhere, the edges of its petals rolled backwards, rather than forward, and this new form revolutionized the dahlia world. It was thought to be a distinct mutation since no other plant that resembled it could be found in the wild.<ref>Michigan Special Bulletin #266. Ag. Exp. Sta. Mich. St. Col. 1935.</ref> Today it is assumed that ''D.&nbsp;juarezii'' had, at one time, existed in Mexico and subsequently disappeared. Nurserymen in Europe crossbred this plant with dahlias discovered earlier; the results became the progenitors of all modern dahlia hybrids today.{{sfn|Weland|2015|loc=p.&nbsp;40}}
=== Award of Garden Merit (RHS) ===
{{main|List of Award of Garden Merit dahlias}}
As of 2015, 124 dahlia cultivars have gained the [[Royal Horticultural Society]]'s [[Award of Garden Merit]],{{sfn|RHS|2015|loc=[http://apps.rhs.org.uk/agm/Award2.asp?User2=Hrb&crit=Dahlia Search for AGM Plants: Dahlia]}} including:
{{div col|colwidth=15em}}
* "Bednall beauty"<ref>{{cite web|url=https://www.rhs.org.uk/Plants/87446/Dahlia-Bednall-Beauty-(Misc-DwB)/Details |title=RHS Plant Selector Dahlia 'Bednall Beauty' (Misc/DwB) AGM / RHS Gardening |publisher=Apps.rhs.org.uk |access-date=2020-04-17}}</ref>
* "[[Dahlia 'Bishop of Llandaff'|Bishop of Llandaff]]"{{sfn|RHS|2015|loc=[https://www.rhs.org.uk/Plants/96238/Dahlia-Bishop-of-Llandaff-(P)/Details ''Dahlia'' 'Bishop of Llandaff' (P)]}}
* "Clair de lune"<ref>{{cite web|url=https://www.rhs.org.uk/Plants/51299/Dahlia-Clair-de-Lune-(Col)/Details |title=RHS Plant Selector Dahlia 'Clair de Lune' (Col) AGM / RHS Gardening |publisher=Apps.rhs.org.uk |access-date=2020-04-17}}</ref>
* "David Howard"<ref>{{cite web|url=https://www.rhs.org.uk/Plants/57111/Dahlia-David-Howard-(D)/Details |title=RHS Plant Selector Dahlia 'David Howard' (MinD) AGM / RHS Gardening |publisher=Apps.rhs.org.uk |access-date=2020-04-17}}</ref>
* "Ellen Huston"<ref>{{cite web|url=https://www.rhs.org.uk/Plants/43463/Dahlia-Ellen-Huston-(Misc-DwB)/Details |title=RHS Plant Selector Dahlia 'Ellen Huston' (Misc/DwB) AGM / RHS Gardening |publisher=Apps.rhs.org.uk |access-date=2020-05-23}}</ref>
* "Fascination"<ref>{{cite web|url=https://www.rhs.org.uk/Plants/227178/Dahlia-Fascination-(P)/Details |title=RHS Plant Selector Dahlia 'Fascination' (P) AGM / RHS Gardening |publisher=Apps.rhs.org.uk |access-date=2020-05-23}}</ref>
* "Gallery Art Deco"<ref>{{cite web|url=https://www.rhs.org.uk/Plants/143517/Dahlia-Gallery-Art-Deco-(PBR)-(Gallery-Series)-(D)/Details |title=RHS Plant Selector Dahlia 'Gallery Art Deco' PBR (Gallery Series) (SD) AGM / RHS Gardening |publisher=Apps.rhs.org.uk |access-date=2020-05-23}}</ref>
* "Gallery Art Nouveau"<ref>{{cite web|url=https://www.rhs.org.uk/Plants/143522/Dahlia-Gallery-Art-Nouveau-(PBR)-(Gallery-Series)-(D)/Details |title=RHS Plant Selector Dahlia 'Gallery Art Nouveau' PBR (Gallery Series) (MinD) AGM / RHS Gardening |publisher=Apps.rhs.org.uk |access-date=2020-05-23}}</ref>
* "Glorie van Heemstede"<ref>{{cite web|url=https://www.rhs.org.uk/Plants/58631/Dahlia-Glorie-van-Heemstede-(WL)/Details |title=RHS Plant Selector Dahlia 'Glorie van Heemstede' (SWL) AGM / RHS Gardening |publisher=Apps.rhs.org.uk |access-date=2020-05-23}}</ref>
* "Honka"<ref>{{cite web |url=http://apps.rhs.org.uk/plantselector/plant?plantid=2649 |archive-url=https://archive.today/20121225005424/http://apps.rhs.org.uk/plantselector/plant?plantid=2649 |url-status=dead |archive-date=2012-12-25 |title=RHS Plant Selector Dahlia 'Honka' (SinO) AGM / RHS Gardening |publisher=Apps.rhs.org.uk |access-date=2013-04-29 }}</ref>
* "[[Dahlia 'Moonfire'|Moonfire]]"{{sfn|RHS|2015|loc=[https://www.rhs.org.uk/Plants/47506/Dahlia-Moonfire-(Sin)/Details ''Dahlia'' 'Moonfire' (Misc/DwB)]}}
* "Twyning's After Eight"{{sfn|RHS|2015|loc=[https://www.rhs.org.uk/Plants/219157/Dahlia-Twyning-s-After-Eight-(Sin)/Details ''Dahlia'' 'Twyning's After Eight' (Sin)]}}
{{div col end}}
==Uses==
The Aztecs used dahlias to treat [[epilepsy]],<ref name=":0" /> and employed the long hollow stem of the ''D.&nbsp;imperialis'' for water pipes.<ref name="autogenerated2002" /> Europeans attempted to introduce the tubers as a food crop, but this was unpopular.<ref>{{Cite web |title=Aztec Dahlias - Dahlia History |url=http://www.aztecdahlias.com/azdahlhistory.htm |url-status=dead |archive-url=https://web.archive.org/web/20170617184659/http://www.aztecdahlias.com/azdahlhistory.htm |archive-date=2017-06-17 |access-date=2013-12-14}}</ref>
The dahlia is considered one of the native ingredients in Oaxacan cuisine; several cultivars are still grown especially for their large, sweet potato-like tubers. Dacopa, an intense mocha-tasting extract from the roasted tubers, is used to flavor beverages throughout [[Central America]].<ref name="autogenerated2002"/>
=== Medicine ===
In Europe and America, prior to the discovery of [[insulin]] in 1923, [[diabetes|diabetics]]—as well as [[tuberculosis|consumptives]]—were often given a substance called ''Atlantic starch'' or ''diabetic sugar'', derived from [[inulin]], a naturally occurring form of [[fructose|fruit sugar]], extracted from dahlia tubers.<ref>{{cite journal |last1= Williams |first1= Francis M. |date= 1895 |title= Report on Therapeutics, On the effect of giving levulose and inulin to patients suffering diabetes mellitus |journal= [[The Boston Medical and Surgical Journal]] |publisher=  [[Massachusetts Medical Society]], New England Surgical Society |volume= 133 |issue=2 |pages= 37|doi= 10.1056/NEJM189507111330204 }}</ref> Inulin is still used in clinical tests for kidney functionality.
==In culture==
Founded in 1936, the [[Bloemencorso Zundert]] is the largest [[flower parade]] in the world entirely made by volunteers using the dahlia. The parade takes place on the first Sunday of September in [[Zundert]], Netherlands. The floats are large artworks made of steel wire, cardboard, [[papier-mâché]] and flowers. In the Bloemencorso Zundert, mostly dahlias are used to decorate the objects and it takes thousands of them just to cover one float. Around 8 million dahlias are needed for the entire corso. Of these, around 6 million are cultivated in Zundert.
The dahlia was declared the [[national flower]] of [[Mexico]] in 1963.<ref>{{cite book |last=Harvey |first=Marian |url=https://books.google.com/books?id=n2EWryQkeXYC |title=Mexican Crafts and Craftspeople |publisher=Associated University Presses |year=1987 |isbn=978-0-87982-512-6 |page=19}}</ref>
==See also==
* [[List of dahlia diseases]]
* [[Plant symbolism|Dahlia symbolism]]
[[File:DAHLIA COLLECTION.jpg|thumb|Dahlias from the UK National Collection of dahlias]]
==References==
{{Reflist|3|refs=
* <ref name=Saar>{{Cite journal|doi=10.1043/01-78.1|jstor=25063902|title=A Phylogenetic Analysis of the Genus Dahlia (Asteraceae) Based on Internal and External Transcribed Spacer Regions of Nuclear Ribosomal DNA|journal=Systematic Botany|volume=28|issue=3|pages=627–639|last1=Saar|first1=Dayle E.|last2=Polans|first2=Neil O.|last3=Sørensen|first3=Paul D.|year=2003|doi-broken-date=1 November 2024}}</ref>
}}
== Bibliography ==
{{refbegin|30em}}
* {{cite web|last1=Bates|first1=Dave|title=The Growing World of Dahlias|url=http://www.dahliaworld.co.uk/|date=2015}}
* {{cite web|title=Linda's Dahlias|url=http://www.lindasdahlias.com/Home_Page.php|access-date=21 June 2015|date=2015|ref={{harvid|Linda's Dahlias|2015}}|archive-url=https://web.archive.org/web/20150621211154/http://www.lindasdahlias.com/Home_Page.php|archive-date=21 June 2015|url-status=dead}}
* {{cite web|last1=Dave's Garden|title=Welcome to Dave's Garden!|url=http://davesgarden.com/|publisher=Internet Brands|access-date=14 June 2015|date=2015}}
* {{cite web|title=The National Dahlia Collection|url=http://www.national-dahlia-collection.co.uk/en/the-collection|access-date=25 June 2015|ref={{harvid|National Dahlia Collection|2015}}|archive-date=11 October 2015|archive-url=https://web.archive.org/web/20151011131811/http://www.national-dahlia-collection.co.uk/en/the-collection|url-status=dead}}
* {{cite web|last1=Culbertson|first1=Tim|title=The Stanford Dahlia Project|url=https://web.stanford.edu/group/dahlia_genetics/index.htm|access-date=2 July 2015|ref={{harvid|Stanford Dahlia Project|2015}}}}
* {{cite web|last1=Fides|title=Fides: Our Roots, Your Success|url=http://www.fides.nl/site|date=2015|access-date=2 July 2015}}
* {{cite web|last1=Dümmen Orange|title=One Mission|url=http://dummenorange.com/|access-date=2 July 2015|date=2015}}
* {{cite web|last1=Dahlinova|title=Welcome at Dahlinova|url=http://dahlinova.com/|access-date=2 July 2015|date=2008}}
=== Articles ===
* {{cite journal|last1=Harshberger|first1=John W.|title=The Native Dahlias of Mexico|journal=Science|series=New Series|date=December 17, 1897|volume=6|issue=155|pages=908–910|jstor=1623914|doi=10.1126/science.6.155.908|pmid=17740849|bibcode=1897Sci.....6..908H|url=https://zenodo.org/record/1448291}}
* Sherff, Earl Edward, 1951: Epiphytum, a new section of the genus Dahlia Cav. Bot Leaflets: 4,21
* {{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 }}
* [https://web.archive.org/web/20140810095901/http://commons.lib.niu.edu/handle/10843/10845 Saar, Dayle Ellyn. A phylogenetic analysis of the genius Dahlia (asteraceae): An interdisciplinary study. Ph D Thesis, Northern Illinois University, 1999]
* {{cite journal |author=Whitley- GR |title=The medicinal and nutritional properties of Dahlia spp |journal=J Ethnopharmacol |volume=14 |issue=1 |pages=75–82 |date=September 1985 |pmid=3910964 |doi=10.1016/0378-8741(85)90031-5}}
* {{cite web|last1=Weland|first1=Gerald|title=The Alpha-Omega of Dahlias|url=https://web.stanford.edu/group/dahlia_genetics/supplemental/the_alpha_and_omega_of_dahlias.pdf|publisher=American Dahlia Society|access-date=2 July 2015|ref={{harvid|Weland|2015}}}}
=== Societies ===
* {{cite web|last1=RHS|title=Royal Horticultural Society|url=https://www.rhs.org.uk/|access-date=19 June 2015|date=2015}}
** [https://www.rhs.org.uk/advice/profile?PID=592 Dahlia]
* {{cite web|title=National Dahlia Society (U.K.)|url=http://www.dahlia-nds.co.uk/index.htm|access-date=17 June 2015|date=2011|ref={{harvid|NDS|2011}}|archive-url=https://web.archive.org/web/20150607195443/http://www.dahlia-nds.co.uk/index.htm|archive-date=7 June 2015|url-status=dead}}
** [http://www.dahlia-nds.co.uk/about_dahlias/Specie_Dahlia.htm Dahlia species; The National Dahlia Society (U.K.)]
* {{cite web|title=The American Dahlia Society|url=http://www.dahlia.org/|access-date=17 June 2015|ref={{harvid|ADS|2015}}}}
* {{cite web|title=National Dahlia Society Of New Zealand|url=http://www.nzdahliasociety.50megs.com/|access-date=17 June 2015|ref={{harvid|NDSNZ|2015}}}}
{{refend}}
==External links==
*{{commons category-inline|Dahlia}}
*{{wikispecies-inline|Dahlia (Asteraceae)|Dahlia}}
*{{wiktionary-inline}}
* [http://wilddahlias.com/Aboutwhilddahlias.html D E Saar. Wild Dahlias]
* [http://www.national-dahlia-collection.co.uk The United Kingdom National Dahlia Collection] {{Webarchive|url=https://web.archive.org/web/20081018203906/http://www.national-dahlia-collection.co.uk/ |date=2008-10-18 }}
* [https://web.archive.org/web/20090828034433/http://www.dahlia.org/index.php?page=dahlia-events-calendar North American Dahlia Shows]
* [https://web.archive.org/web/20070614203633/http://www.homegardenguides.com/wiki/Dahlia Dahlia] Flower Care
* [https://www.eattheweeds.com/dahlia-pinnata/ Dahlia Pinnata Eatable Plans]
* [https://web.archive.org/web/20070102213714/http://www.theflowerbulb.com/plants/Dahlia.php Info about care for dahlias]
** [https://web.archive.org/web/20070428210448/http://ibiblio.org/pfaf/cgi-bin/arr_html?Dahlia+rosea&CAN=LATIND ''Dahlia rosea'' at pfaf]
** [https://web.archive.org/web/20070428210422/http://ibiblio.org/pfaf/cgi-bin/arr_html?Dahlia+pinnata&CAN=LATIND ''Dahlia pinnata'' at pfaf]
* [https://web.archive.org/web/20080724081108/http://www.dahlia.com/gallery2/ Gallery of Dahlia Images]
* [http://apps.rhs.org.uk/planttrials/TrialReports/Dahlia%202008.pdf Hans V. Hansen. Native (wild) Dahlias – taxonomy, historical review, and the derivation of cultivars, in Trial of Dahlia 2008, Final Report. Royal Horticultural Society] {{Webarchive|url=https://web.archive.org/web/20140811212615/http://apps.rhs.org.uk/planttrials/TrialReports/Dahlia%202008.pdf |date=2014-08-11 }}
* [https://web.archive.org/web/20160418212045/https://bigbooklet.com/dahlia.html A history of Dahlia, from «Oxford Junior Encyclopedia»]
=== Databases ===
* [https://www.compositae.org/gcd/aphia.php?p=taxdetails&id=1075641  Global Compositae Database]
{{Taxonbar|from=Q130918}}
{{Authority control}}
[[Category:Dahlia| ]]
[[Category:Asteraceae genera]]
[[Category:Crops originating from Mexico]]
[[Category:Oaxacan cuisine]]
[[Category:Garden plants of North America]]
[[Category:National symbols of Mexico]]
[[Category:Perennial plants]]
[[Category:Flora of Mexico]]
[[Category:Flora of Southern America]]
[[Category:Plants used in Native American cuisine]]
[[Category:Crops originating from indigenous Americans]]
[[Category:Taxa named by Antonio José Cavanilles]]