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Dahlia (, ) is a
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
of bushy,
tuberous Tubers are a type of enlarged structure used as storage organs for nutrients in some plants. They are used for the plant's perennation (survival of the winter or dry months), to provide energy and nutrients for regrowth during the next growing s ...
,
herbaceous Herbaceous plants are vascular plants that have no persistent woody stems above ground. This broad category of plants includes many perennials, and nearly all annuals and biennials. Definitions of "herb" and "herbaceous" The fourth edition o ...
perennial plant A perennial plant or simply perennial is a plant that lives more than two years. The term ('' per-'' + '' -ennial'', "through the years") is often used to differentiate a plant from shorter-lived annuals and biennials. The term is also wide ...
s native to Mexico and Central America. A member of the
Asteraceae The family Asteraceae, alternatively Compositae, consists of over 32,000 known species of flowering plants in over 1,900 genera within the order Asterales. Commonly referred to as the aster, daisy, composite, or sunflower family, Compositae ...
(former name: Compositae) family of
dicotyledon The dicotyledons, also known as dicots (or, more rarely, dicotyls), are one of the two groups into which all the flowering plants (angiosperms) were formerly divided. The name refers to one of the typical characteristics of the group: namely, t ...
ous plants, its garden relatives thus include the
sunflower The common sunflower (''Helianthus annuus'') is a large annual forb of the genus ''Helianthus'' grown as a crop for its edible oily seeds. Apart from cooking oil production, it is also used as livestock forage (as a meal or a silage plant), ...
,
daisy Daisy, Daisies or DAISY may refer to: Plants * ''Bellis perennis'', the common daisy, lawn daisy or English daisy, a European species Other plants known as daisy * Asteraceae, daisy family ** '' Euryops chrysanthemoides'', African bush daisy ** ' ...
, chrysanthemum, and
zinnia ''Zinnia'' is a genus of plants of the tribe Heliantheae within the family Asteraceae. They are native to scrub and dry grassland in an area stretching from the Southwestern United States to South America, with a centre of diversity in Mexi ...
. There are 49
species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...
of this genus, with hybrids commonly grown as garden plants. Flower forms are variable, with one head per stem; these can be as small as diameter or up to ("dinner plate"). This great variety results from dahlias being octoploids—that is, they have eight sets of homologous
chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins ar ...
s, whereas most plants have only two. In addition, dahlias also contain many
transposons A transposable element (TE, transposon, or jumping gene) is a nucleic acid sequence in DNA that can change its position within a genome, sometimes creating or reversing mutations and altering the cell's genetic identity and genome size. Tran ...
—genetic pieces that move from place to place upon an
allele An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution. ::"The chrom ...
—which contributes to their manifesting such great diversity. The stems are leafy, ranging in height from as low as to more than . The majority of species do not produce scented flowers. Like most plants that do not attract
pollinating Pollination is the transfer of pollen from an anther of a plant to the stigma of a plant, later enabling fertilisation and the production of seeds, most often by an animal or by wind. Pollinating agents can be animals such as insects, birds, a ...
insects through scent, they are brightly colored, displaying most hues, with the exception of blue. The dahlia was declared the
national flower In a number of countries, plants have been chosen as symbols to represent specific geographic areas. Some countries have a country-wide floral emblem; others in addition have symbols representing subdivisions. Different processes have been used to ...
of
Mexico Mexico (Spanish language, Spanish: México), officially the United Mexican States, is a List of sovereign states, country in the southern portion of North America. It is borders of Mexico, bordered to the north by the United States; to the so ...
in 1963. The tubers were grown as a food crop by the
Aztecs The Aztecs () were a Mesoamerican culture that flourished in central Mexico in the post-classic period from 1300 to 1521. The Aztec people included different ethnic groups of central Mexico, particularly those groups who spoke the Nahuatl ...
, but this use largely died out after the Spanish Conquest. Attempts to introduce the tubers as a food crop in Europe were unsuccessful.


Description

Dahlias are perennial plants with tuberous roots, though they are grown as annuals in some 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. As a member of the
Asteraceae The family Asteraceae, alternatively Compositae, consists of over 32,000 known species of flowering plants in over 1,900 genera within the order Asterales. Commonly referred to as the aster, daisy, composite, or sunflower family, Compositae ...
, the dahlia has a flower head that is actually a composite (hence the older name Compositae) with both central disc
floret This glossary of botanical terms is a list of definitions of terms and concepts relevant to botany and plants in general. Terms of plant morphology are included here as well as at the more specific Glossary of plant morphology and Glossary o ...
s and surrounding ray florets. Each floret is a flower in its own right, but is often incorrectly described as a petal, particularly by horticulturists. The modern name Asteraceae refers to the appearance of a star with surrounding rays.


Taxonomy


History


Early history

Spaniards reported finding the plants growing in Mexico in 1525, but the earliest known description is by Francisco Hernández, physician to 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, and were both gathered in the wild and cultivated. The Aztecs used them to treat epilepsy, and employed the long hollow stem of the '' Dahlia imperialis'' for water pipes.Katz, Solomon H.; Weaver, William Woys Weaver, Encyclopedia of Food and Culture, The Gale Group, New York, 2002. The indigenous peoples variously identified the plants as "Chichipatl" (
Toltecs The Toltec culture () was a pre-Columbian Mesoamerican culture that ruled a state centered in Tula, Hidalgo, Mexico, during the Epiclassic and the early Post-Classic period of Mesoamerican chronology, reaching prominence from 950 to 1150 CE ...
) and "Acocotle" or "Cocoxochitl" (Aztecs). From Hernandez's perception of Aztec, to Spanish, through various other translations, the word is "water cane", "water pipe", "water pipe flower", "hollow stem flower" and "cane flower". All these refer to the hollowness of the plants' stem. 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, a 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. In 1578 the manuscript, entitled ''Nova Plantarum, Animalium et Mineralium Mexicanorum Historia'', was sent back to the Escorial in Madrid; they were not translated into Latin by Francisco Ximenes until 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 in two volumes as ''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.


European introduction

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. In 1789,
Vicente Cervantes Vicente (Vincente) de Cervantes (Ledrada, Salamanca España; 1755 - México; 1829) was a notable Spanish and Mexican physician and botanist. Background Don Vicente Cervantes was a contemporary of Martín Sessé y Lacasta and corresponded with Je ...
, Director of the Botanical Garden at Mexico City, sent "plant parts" to Abbe Antonio José Cavanilles, Director of the Royal Gardens of Madrid. Cavanilles flowered one plant that same year, then the second one a year later. In 1791 he called the new growths "Dahlia" for Anders (Andreas) Dahl. The first plant was called ''Dahlia pinnata'' after its
pinnate Pinnation (also called pennation) is the arrangement of feather-like or multi-divided features arising from both sides of a common axis. Pinnation occurs in biological morphology, in crystals, such as some forms of ice or metal crystals, an ...
foliage; the second, ''Dahlia rosea'' for its rose-purple color. In 1796 Cavanilles flowered a third plant from the parts sent by Cervantes, which he named ''Dahlia coccinea'' for its scarlet color. In 1798, Cavanilles sent D. pinnata seeds to
Parma Parma (; egl, Pärma, ) is a city in the northern Italian region of Emilia-Romagna known for its architecture, music, art, prosciutto (ham), cheese and surrounding countryside. With a population of 198,292 inhabitants, Parma is the second m ...
, Italy. That year, the Marchioness of Bute, wife of 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.Dean, Richard, The dahlia: its history and cultivation, Macmillan, 1897, p.5. 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. pinnata, D. rosea, D. 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 William Aiton (17312 February 1793) was a Scottish botanist. Aiton was born near Hamilton. Having been regularly trained to the profession of a gardener, he travelled to London in 1754, and became assistant to Philip Miller, then superinten ...
at Kew Gardens. That same year, John Fraser, English nurseryman and later botanical collector to the Czar of Russia, brought '' D. coccinea'' seeds from Paris to the 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, Kensington. Whilst in Madrid in 1804, Lady Holland was given either dahlia seeds or tubers by Cavanilles. She sent them back to England, to Lord Holland's librarian Mr Buonaiuti at Holland House, who successfully raised the plants. A year later, Buonaiuti produced two double flowers. The plants raised in 1804 did not survive; new stock was brought from France in 1815. In 1824, Lord Holland sent his wife a note containing the following verse:
"The dahlia you brought to our isle
Your praises for ever shall speak;
Mid gardens as sweet as your smile,
And in colour as bright as your cheek."
In 1805, German naturalist
Alexander von Humboldt Friedrich Wilhelm Heinrich Alexander von Humboldt (14 September 17696 May 1859) was a German polymath, geographer, naturalist, explorer, and proponent of Romantic philosophy and science. He was the younger brother of the Prussian minister ...
sent more seeds from Mexico to Aiton in England, Thouin in Paris, and
Christoph Friedrich Otto Christoph Friedrich Otto (4 December 1783 – 7 December 1856) was a German gardener and botanist. He was born in Schneeberg, Saxony. From 1805 to 1843 he was inspector of the Botanical Garden in Berlin. Together with Albert Gottfried Dietrich ...
, director of the
Berlin Botanical Garden The Berlin Botanic Garden and Botanical Museum (german: Botanischer Garten und Botanisches Museum Berlin) is a botanical garden in the locality of the borough of , Berlin, Germany. Constructed between 1897 and 1910 under the guidance of arc ...
. More significantly, he sent seeds to botanist
Carl Ludwig Willdenow Carl Ludwig Willdenow (22 August 1765 – 10 July 1812) was a German botanist, pharmacist, and plant taxonomist. He is considered one of the founders of phytogeography, the study of the geographic distribution of plants. Willdenow was ...
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. pinnata'' and ''D. rosea'' under the name of ''Georgina variabilis''; ''D. coccinea'' was still held to be a separate species, which he renamed ''Georgina coccinea''.


Classification

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 hybrids, 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. 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. In 1829, all species growing in Europe were reclassified under an all-encompassing name of ''D. variabilis, Desf.'', though this is not an accepted name. 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 a botanist named Liberty Hyde Bailey. (Dr. Walbot). 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. 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).


Circumscription

The genus ''Dahlia'' is situated in the Asteroideae
subfamily In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus Genus ( plural genera ) is a taxonomic rank used in the biological classifica ...
of the
Asteraceae The family Asteraceae, alternatively Compositae, consists of over 32,000 known species of flowering plants in over 1,900 genera within the order Asterales. Commonly referred to as the aster, daisy, composite, or sunflower family, Compositae ...
, in the
Coreopsideae Coreopsideae is a tribe of flowering plants belonging to the Asteroideae subfamily. It includes widely cultivated genera such as ''Cosmos'' and '' Dahlia''. A similar group has been recognized since 1829, generally as part of the tribe Heliant ...
tribe The term tribe is used in many different contexts to refer to a category of human social group. The predominant worldwide usage of the term in English is in the discipline of anthropology. This definition is contested, in part due to confl ...
. Within that tribe it is the second largest genus, after ''Coreopsis'', and appears as a well defined
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English ter ...
within the Coreopsideae.


Subdivision


Infrageneric subdivision

Sherff (1955), in the first modern taxonomy described three sections for the 18 species he recognised, ''Pseudodendron'', ''Epiphytum'' and ''Dahlia''. By 1969 Sørensen recognised 29 species and four sections by splitting off ''Entemophyllon'' from section ''Dahlia''. By contrast Giannasi (1975) using a phytochemical analysis based on
flavonoids Flavonoids (or bioflavonoids; from the Latin word ''flavus'', meaning yellow, their color in nature) are a class of polyphenolic secondary metabolites found in plants, and thus commonly consumed in the diets of humans. Chemically, flavonoids ...
, reduced the genus to just two sections, ''Entemophyllon'' and ''Dahlia'', the latter having three subsections, ''Pseudodendron'', ''Dahlia'', and ''Merckii''. Sørensen then issued a further revision in 1980, incorporating subsection ''Merckii'' in his original section ''Dahlia''. When he described two new species in the 1980s ('' Dahlia tubulata'' and '' D. congestifolia''), he placed them within his existing sections. A further species, '' Dahlia sorensenii'' was added by Hansen and Hjerting in (1996). At the same time they demonstrated that '' Dahlia pinnata'' should more properly be designated ''D. x pinnata''. ''D. x pinnata'' was shown to actually be a variant of ''D. sorensenii'' that had acquired hybrid qualities before it was introduced to Europe in the sixteenth century and formally named by Cavanilles. The original wild ''D. pinnata'' is presumed extinct. Further species continue to be described, Saar (2003) describing 35 species. However separation of the sections on morphological, cytologal and biocemical criteria has not been entirely satisfactory. To date these sectional divisions have not been fully supported phylogenetically, which demonstrate only section ''Entemophyllon'' as a distinct sectional
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English ter ...
. 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. tubulata'' and ''D. merckii'' as a polytomy. 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'').


= Sections

= Sections (including chromosome numbers), with geographical distribution; * ''Epiphytum'' Sherff (2n = 32) **10 m tall climber with aerial roots 5 cm thick and up to more than 20 m long; pinnules opposite ** 1 species, ''D. 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. 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'' (''D. imperialis'') and ''Dahlia'' (''D. australis'', ''D. coccinea'') occur outside Mexico.


=Species

= There are currently 42 accepted species in the genus ''Dahlia'' but new species continue to be described.


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 Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his ennoblement in 1761 as Carl von Linné Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalised binomial nomenclature, ...
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, 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. Regardless of who bestowed it, the name was not so easily established. In 1805, German botanist
Carl Ludwig Willdenow Carl Ludwig Willdenow (22 August 1765 – 10 July 1812) was a German botanist, pharmacist, and plant taxonomist. He is considered one of the founders of phytogeography, the study of the geographic distribution of plants. Willdenow was ...
, 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
German German(s) may refer to: * Germany (of or related to) **Germania (historical use) * Germans, citizens of Germany, people of German ancestry, or native speakers of the German language ** For citizens of Germany, see also German nationality law **Ge ...
-born naturalist Johann Gottlieb Georgi, a professor at the Imperial Academy of Sciences of St. Petersburg,
Russia Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the largest country in the world, with its internationally recognised territory covering , and encompassing one-ei ...
). 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''. However, the name ''Georgina'' still persisted in Germany for the next few decades. In Russian, it is still named Georgina (russian: георгинa). "Dahl" is a homophone of the Swedish word "dal", or "valley"; although it is not a true translation, the plant is sometimes referred to as the "valley flower".


Distribution and habitat

''Dahlia'' is found predominantly in
Mexico Mexico (Spanish language, Spanish: México), officially the United Mexican States, is a List of sovereign states, country in the southern portion of North America. It is borders of Mexico, bordered to the north by the United States; to the so ...
, but some species are found ranging as far south as northern
South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sou ...
. '' D. australis'' occurs at least as far south as southwestern
Guatemala Guatemala ( ; ), officially the Republic of Guatemala ( es, República de Guatemala, links=no), is a country in Central America. It is bordered to the north and west by Mexico; to the northeast by Belize and the Caribbean; to the east by Hon ...
, while '' D. coccinea'' and '' D. imperialis'' also occur in parts of
Central America Central America ( es, América Central or ) is a subregion of the Americas. Its boundaries are defined as bordering the United States to the north, Colombia to the south, the Caribbean Sea to the east, and the Pacific Ocean to the west. ...
and northern South America. ''Dahlia'' is a genus of the uplands and mountains, being found at elevations between 1,500 and 3,700 meters, in what has been described as a "pine-oak woodland" vegetative zone. Most species have limited ranges scattered throughout many mountain ranges in Mexico


Ecology

The most common pollinators are bees and small beetles.


Pests and diseases

Slugs Slug, or land slug, is a common name for any apparently shell-less terrestrial molluscs, terrestrial gastropod mollusc. The word ''slug'' is also often used as part of the common name of any gastropod mollusc that has no shell, a very reduced ...
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. 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 bugs (resulting in contortion and holes at growing tips). Diseases affecting dahlias include powdery mildew, grey mould (''
Botrytis cinerea ''Botrytis cinerea'' is a necrotrophic fungus that affects many plant species, although its most notable hosts may be wine grapes. In viticulture, it is commonly known as "botrytis bunch rot"; in horticulture, it is usually called "grey mould" or ...
''),
verticillium ''Verticillium'' is a genus of fungi in the division Ascomycota, and are an anamorphic form of the family Plectosphaerellaceae. The genus used to include diverse groups comprising saprobes and parasites of higher plants, insects, nematodes, moll ...
wilt, dahlia smut (''Entyloma calendulae'' f. ''dahliae''), phytophthora and some plant viruses. Dahlias are a source of food for the
larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. ...
e of some
Lepidoptera Lepidoptera ( ) is an order of insects that includes butterflies and moths (both are called lepidopterans). About 180,000 species of the Lepidoptera are described, in 126 families and 46 superfamilies, 10 percent of the total described speci ...
species including angle shades, common swift, ghost moth and
large yellow underwing The large yellow underwing (''Noctua pronuba'') is a moth, the type species for the family Noctuidae. It is an abundant species throughout the Palearctic realm, one of the most common and most familiar moths of the region. In some years the speci ...
.


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 Dormancy is a period in an organism's life cycle when growth, development, and (in animals) physical activity are temporarily stopped. This minimizes metabolic activity and therefore helps an organism to conserve energy. Dormancy tends to be c ...
, 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 (10 – 15 cm) 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 regularly, once flowering commences.


Horticultural classification


History

The inappropriate term ''D. variabilis'' is often used to describe the cultivars of ''Dahlia'' since the correct parentage remains obscure, but probably involves ''
Dahlia coccinea ''Dahlia coccinea'' is a species of flowering plant in the daisy family Asteraceae. Its common name is red dahlia, although the flowers can be orange or occasionally yellow, as well as the more common red. The species is native to Mexico but has ...
''. In 1846 the Caledonia Horticultural Society of
Edinburgh Edinburgh ( ; gd, Dùn Èideann ) is the capital city of Scotland and one of its 32 Council areas of Scotland, council areas. Historically part of the county of Midlothian (interchangeably Edinburghshire before 1921), it is located in Lothian ...
offered a prize of 2,000 pounds to the first person succeeding in producing a blue dahlia. This has to date not been accomplished. While dahlias produce
anthocyanin Anthocyanins (), also called anthocyans, are water-soluble vacuolar pigments that, depending on their pH, may appear red, purple, blue, or black. In 1835, the German pharmacist Ludwig Clamor Marquart gave the name Anthokyan to a chemical com ...
, an element necessary for the production of the blue, to achieve a true blue color in a plant, the anthocyanin delphinidin needs six
hydroxyl In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydrox ...
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. 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. 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. Fimbriated dahlias were added in 2004, and two further groups (Single and Double orchid) in 2007. The last group to be added, Peony, first appeared in 2012. In many cases the bloom diameter was then used to further label certain groups from miniature to giant. This practice was abandoned in 2012.


Modern system (RHS)

There are now more than 57,000 registered
cultivars A cultivar is a type of cultivated plant that people have selected for desired traits and when propagated retain those traits. Methods used to propagate cultivars include: division, root and stem cuttings, offsets, grafting, tissue culture, ...
, which are officially registered through the
Royal Horticultural Society The Royal Horticultural Society (RHS), founded in 1804 as the Horticultural Society of London, is the UK's leading gardening charity. The RHS promotes horticulture through its five gardens at Wisley (Surrey), Hyde Hall (Essex), Harlow Carr (Nor ...
(RHS). 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. Since then about a hundred new cultivars are added annually. ;Flower type The official RHS classification lists fourteen groups, grouped by flower type, together with the abbreviations used by the RHS; ;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’. Some Dahlia Societies have continued this practice, but this is neither official nor standardised. As of 2013 The RHS uses two size descriptors * Dwarf Bedder (Dw.B.) – not usually exceeding in height, ''e.g.'' 'Preston Park' (''Sin/DwB'') * Lilliput dahlias (Lil) – not usually exceeding in height, with single, semi-double or double florets up to in diameter. ("baby" or "top-mix" dahlias), ''e.g.'' 'Harvest Tiny Tot' (''Misc/Lil'') Sizes can range from tiny micro dahlias with flowers less than 50mm to giants that are over 250mm in diameter. The groupings listed here are from the New Zealand Society: * Giant-flowered cultivars have blooms with a diameter over 250 mm. * Large-flowered cultivars have blooms with a diameter of 200–250 mm. * Medium-flowered cultivars have blooms with a diameter of 155–350 mm. * Small-flowered cultivars have blooms with a diameter of 115–155 mm. * Miniature-flowered cultivars have blooms with a diameter of 50–115 mm. * Pompom-flowered cultivars have blooms with a diameter less than 50 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.


Branding

Some plant growers include their brand name in the cultivar name. Thus Fides (part of the Dümmen Orange Group) in the Netherlands developed a series of cultivars which they named the Dahlinova series, for example Dahlinova 'Carolina Burgundy'. These are Group 10 Miscellaneous in the RHS classification scheme.


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. Many of the species of dahlias then, and now, have single-flowered blooms. ''D. 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. 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
Louvain Leuven (, ) or Louvain (, , ; german: link=no, Löwen ) is the capital and largest city of the province of Flemish Brabant in the Flemish Region of Belgium. It is located about east of Brussels. The municipality itself comprises the historic c ...
, selected plants for that characteristic, and within a few years secured three fully double forms. 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. ''D. crocea'', a fragrant variety grown from one of the Humboldt seeds, was probably interbred with the single ''D. coccinea''. A new scented species would not be introduced until the next century when the ''D. coronata'' was brought from Mexico to Germany in 1907. 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. coccinea speciosissima'' grown by William Leathe, of Cambridgeport, near Boston, around 1929. According to Edward Sayers, "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, 9 cultivars were already listed in the catalog from Thornburn, 1825. 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. 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. 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. In 1835 Thomas Bridgeman, published a list of 160 double dahlias in his "Florist's Guide". 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".


"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." 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) 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. Today it is assumed that ''D. 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.


Award of Garden Merit (RHS)

As of 2015, 124 dahlia cultivars have gained the
Royal Horticultural Society The Royal Horticultural Society (RHS), founded in 1804 as the Horticultural Society of London, is the UK's leading gardening charity. The RHS promotes horticulture through its five gardens at Wisley (Surrey), Hyde Hall (Essex), Harlow Carr (Nor ...
's
Award of Garden Merit The Award of Garden Merit (AGM) is a long-established annual award for plants by the British Royal Horticultural Society (RHS). It is based on assessment of the plants' performance under UK growing conditions. History The Award of Garden Merit ...
, including:- * "Bednall beauty" * " Bishop of Llandaff" * "Clair de lune" * "David Howard" * "Ellen Huston" * "Fascination" * "Gallery Art Deco" * "Gallery Art Nouveau" * "Glorie van Heemstede" * "Honka" * " Moonfire" * "Twyning's After Eight"


Uses


Floriculture

The asterid eudicots contain two economically important
geophyte A storage organ is a part of a plant specifically modified for storage of energy (generally in the form of carbohydrates) or water. Storage organs often grow underground, where they are better protected from attack by herbivores. Plants that have ...
genera, ''Dahlia'' and ''
Liatris ''Liatris'' (), commonly known as gayfeather and blazing star. is a genus of flowering plants in the tribe Eupatorieae within the family Asteraceae native to North America (Canada, United States, Mexico and the Bahamas). Some species are used ...
''. Horticulturally the garden dahlia is usually treated as the cultigen ''D. variabilis'' hort., which while being responsible for thousands of cultivars has an obscure taxonomic status (see also Cultivation).


Other

Today the dahlia is still 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 Central America ( es, América Central or ) is a subregion of the Americas. Its boundaries are defined as bordering the United States to the north, Colombia to the south, the Caribbean Sea to the east, and the Pacific Ocean to the west. ...
. In Europe and America, prior to the discovery of
insulin Insulin (, from Latin ''insula'', 'island') is a peptide hormone produced by beta cells of the pancreatic islets encoded in humans by the ''INS'' gene. It is considered to be the main anabolic hormone of the body. It regulates the metabolism ...
in 1923, diabetics—as well as consumptives—were often given a substance called ''Atlantic starch'' or ''diabetic sugar'', derived from inulin, a naturally occurring form of fruit sugar, extracted from dahlia tubers. Inulin is still used in clinical tests for kidney functionality.


Bloemencorso Zundert

The Bloemencorso Zundert is the largest
flower parade A flower parade is a parade in which the floats, vehicles, boats, participants, animals and other things are decorated or covered in flowers. Often there are other elements like marching bands and people in costumes. Flower parades are held in ...
in the world entirely made by volunteers using the dahlia. The parade takes place on the first Sunday of September in Zundert,
Netherlands ) , anthem = ( en, "William of Nassau") , image_map = , map_caption = , subdivision_type = Sovereign state , subdivision_name = Kingdom of the Netherlands , established_title = Before independence , established_date = Spanish Netherl ...
. 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. It was founded in 1936.


Name

The flower species ''Dahlia'' is also a name used for children, especially daughters. The Swedish word ''dal'' means val, so Dahlia is sometimes referred to as ''valley flower''. The Dahlia symbolizes eternal bonds of commitment, so it is a popular flower of choice for weddings. Dahlia was first listed on the American female naming charts in 2006. The name's popularity has skyrocketed since around 2005. Since 2016, the number of babies named Dahlia per year has stayed at 839. It has reached the top 10 female baby names only once, but is still popular, especially in Montana, Alaska, Maine, and Rhode Island.


See also

* List of dahlia diseases * Dahlia symbolism


References


Bibliography

* * * * * * * *


Articles

* * Sherff, Earl Edward, 1951: Epiphytum, a new section of the genus Dahlia Cav. Bot Leaflets: 4,21 *
Saar, Dayle Ellyn. A phylogenetic analysis of the genius Dahlia (asteraceae): An interdisciplinary study. Ph D Thesis, Northern Illinois University, 1999
* *


Societies

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Dahlia
* *

* *


External links

* *


The United Kingdom National Dahlia Collection

North American Dahlia Shows

Dahlia
Flower Care
Dahlia Pinnata Eatable Plans

Info about care for dahlias
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''Dahlia rosea'' at pfaf
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''Dahlia pinnata'' at pfaf

Gallery of Dahlia Images

Hans V. Hansen. Native (wild) Dahlias – taxonomy, historical review, and the derivation of cultivars, in Trial of Dahlia 2008, Final Report. Royal Horticultural Society



Databases


Global Compositae Checklist
{{Authority control Asteraceae genera Crops originating from Mexico Oaxacan cuisine Garden plants of North America National symbols of Mexico Perennial plants Flora of Mexico Flora of South America Plants used in Native American cuisine Crops originating from indigenous Americans Taxa named by Antonio José Cavanilles