A Short History of Dahlia Hybridization

The following is an adaptation of a wonderful and incredibly conclusive, well-referenced document prepared by Gerald Weland for the American Dahlia Society. Titled "The Alpha and Omega of Dahlias", the original document is a 51 page treatise on the history of Dahlias. It is highly recommended reading after these paraphrased notes and is available here.
This document is divided into sections based on the major floral types of dahlias:

Double | Cactus | Single | Collarette | Orchid
Anemone | Paeony | Mignon | Water Lily

          History of Discovery and Nomenclature

          Dahlia as a genus traces its ancestry to D. zimpanii. This simple or primitive species is morphologically closely related to plants in the genus Bidens, with identifying similarities in leaf shape, achene shape and pappus structure. Some initial confusion regarding the placement of this species relegated it at one point to the genus Bidens (as B. dahliaoides), in 1890. Other early systematists placed the genus close to Cosmos or Coreopsis. In addition to D. zimpanii, which is currently placed in Dahlia, there are some 20 additional species in the genus, and classifications of them have been quite varied throughout their history.

          The earliest western record of Dahlias comes from the physician Francisco Hernandez in 1570:

          The location referred to was later discovered by Harshberger to be the Sierra de Ajusco range in Mexico. The plants described were illustrated by Francisco Dominguez who accompanied Hernandez on a portion of his seven-year study of Mexican flora, and include many drawings showing marked degrees of doubling of ray flowers.

          The earliest known treatment of Dahlia dates to 1791, when Cavanilles, the Director of the Royal Gardens of Madrid described the original type of the genus as Dahlia pinnata, followed closed by D. rosea and D. coccinea in the same year based on grown tubers received from Cervantes collected from Mexico. The genus is named in honor of Andreas Dahl, a botanist and student of Linnaeus. In 1804; Willdenow re-described these three species, combining D. pinnata and D. rosea under the name Georgina variabilis, and calling D. coccinea Georgina coccinea. He believed Cavanilles has used an incorrect name (the genus Dalea is a group of pea-type plants), and honored the Russian botanist Dr. Georgi with his new appellation. He noted that early species were self-incompatible, requiring out-crossing to produce seed, which in turn produced considerable variation in the progeny, thus the name “variabilis.”

          In the same year, 1804, Thouin pictured and described three plants, which he called D. pinnata, D rosea, and D. purpurea, omitting D. coccinea. In 1808 Salisbury listed and described four species, using D. sambucifolia in lieu of D. pinnata and D. bidentifolia in lieu of D. coccinea. In 1809 Willdenow revised his original description to include varieties of his umbrella species Georgina variabilis, and in 1810 revised yet again from the genus Georgina to the genus Dahlia.

          In 1810 Aiton renamed D. pinnata and D. rosea as Dahlia superflua, and D. coccinea as D. frustanea, both of which were corroborated by DeCandolle and the editors of Curtis’ Botanical Magazine in 1817 as the only species in the genus.

          It appears as though much of this earlier confusion was confounded by rapid “discovery” of a number of new species, such that by the year 1829 no less than 22 different species has been described. In effect, all of these were later sunk into just a few species, with Dahlia variabilis the apparent choice to describe an extremely variable group of plants and flowers. De Candolle settled these disputes by publishing D. variabilis, D. coccinea, and D. cervantessii in 1836, in a treatment which remained uncontested for 43 years. These dahlias probably serve as the progenitors of modern day hybrids, and species described later have not played so pivotal a role.

          As of the present, Dahlias are classified based on Bailey into 15 species and six additional recordings for which insufficient data exists to verify accounts. It is common practice to change species names when warranted. Plant taxonomists are continually re-evaluating established genera and species and frequently decide, on the basis of available evidence, that what had been considered to be a single genera or species should be divided into two or more, or that several genera or several species should be combined into one. This is what happened to early dahlias, especially with the adoption of the name D. variabilis in 1829.

          Double | example - Formal Decorative | example - Informal Decorative

          Double forms, including Formal and Informal Decorative ostensibly have resulted from a hybrid involving D. pinnata and an early, possibly misnamed introduction of what was later termed D. coronata. Dahlia pinnata has naturally occurring multi-petaled forms; the D. coronata parent would therefore be to blame for the huge variety of colors exhibited by this group. There is some discrepancy as to who the other parent of the show double dahlia was; D. pinnata is certainly one parent. Dahlia coronata has been advanced as the other parent because it hybridizes easily with D. pinnata, and it is taxonomically close to D. pinnata, possibly hybridizing with it and other dahlias in the wild (a putative introgressed D. coccinea with some infusion of D. coronata has reported at least once in early 1845).

          During the years 1805 to 1810 several people claimed to have produced a double dahlia. Henry C. Andrews in 1805 made a drawing which has been referred to as the first Informal Decorative dahlia. Like other doubles of the time this shows twisting and turning of the florets with a large disc at the center. The drawing was made from a plant in the collection of Lady Holland grown from seeds he had sent from Madrid in May 1804. It must be stated that this dahlia in no way resembles the dahlias of that classification today. It was subsequently identified as D. pinnata; in addition to the winged leaves the foliage was quite dark, both features being highly characteristic of Dahlia pinnata, as well as the later Paeony-flowered dahlias.

          Additionally, Buonaiuti obtained double flowers of two seedlings in 1805 and F. Otto received the first double dahlia from Stuttgart, but produced one of his own in 1809. Otto reported the first double dahlia was obtained by Hartwig of Karlsruhe in 1808¸ and that Donckelaar obtained double forms about the same time. These are rather confusing statements as we know the earliest pictured dahlias were of double form. Could they have been referring to “fully doubled” forms? The credit for developing the first “fully double” appears to belong to the Belgians. Donckelaar, Director of the Botanic Garden at Louvain, selected plants for "doubleness" and sowed a large number of seed each year and within a few years secured three fully double forms. Hammersmith Nurseries in England produced a purple double dahlia called D. purpurea superba in 1816. By 1819 C. Arentz of Leyden, Holland had produced 72 different varieties and by 1821 the first double white dahlia. This was introduced to commerce in 1821 by A.C. Eeden and Son of Haarlem Holland under the name ‘Waverly’. By 1820 Donckelaar had produced more than 50 double varieties. In 1826 Reider reported there were over 100 varieties being grown in Germany.

          By 1826 double varieties were being grown almost exclusively, and there was very little interest in the single forms. However, up to this time all the double dahlias had been purple or tinged with purple; it was reported that "the new scarlets are perfectly pure," and so red-flowered doubles had begun to be produced. In this same year the first Anemone-flowered dahlia was reported by Drummond of Cork, Ireland and was pictured in a drawing by E.D. Smith and Riley published in 1822. This was a curiously shaped dahlia with two whorls of flat recurving rays issuing from and completely covering the disc. It was an extremely dark red variety named ‘Bella Donna’. In order to gain control of this “new” dahlia, J. Lee Hammersmith Nurseries of England purchased the complete stock of Mr. Drummond. Although this was referred to as “the first anemone-flowered dahlia” it was not until 1896 that Garden Chronicle described a new dahlia in which the disc florets were actually quilled as we know the anemone-flowered dahlia today. By 1828, plants of new varieties sold at prices from $2.50 to $25.00 in England.

          In 1829, The Florist's Guide and Cultivator's Directory shows a picture of a dark red "globe-flowered" dahlia. This was the first dahlia of the show type and was grown at the J. Lee Hammersmith Nursery in England and reported as Georgina variabilis var. sphaerocephala. Prior to this, dahlias were generally referred to as single, double or by several names which were subsequently discontinued. Harrison describes this flower in 1831 as “pink” and listed under the name ‘Springfield Rival’. The same publication also listed a second class of this type dahlia which was of several different color combinations, including variegated, bi-color or tinted with a modifying color of a pure ground (blends) which became known as the “Fancy Dahlia”.

          In 1831 another new type dahlia appeared in England. It was a bi-color (crimson with white tips) named ‘Levick’s Incomparable’. In 1832 a bi-color of single form where the maroon scarlet florets were edged white appeared; it was named ‘The Paragon’. Shortly thereafter a classification of dahlias issued in Germany listed several new forms of dahlias including the anemone-flowered, clematis-flowered, rose-flowered, carnation-flowered, aster-flowered, ranunculus-flowered, paeony- flowered, helianthus-flowered, camellia-flowered, pyrethum-flowered, poppy- flowered, hollyhock-flowered and globe-flowered. However, the newly formed Metropolitan Dahlia Society of England ruled that many of those forms were not eligible for prizes, signaling the annihilation of sales of many of those forms and concentrating public attention on the ranunculus-flowered type from which the Show dahlia was developed. It has been estimated that by 1834 over 20,000 seedlings of dahlia were grown annually in England alone.

          In 1841, Joseph Harrison reported that complete control of the stock of a new variety of merit was sold for as much as $2,500.00. An anonymous report in the Garden Chronicle of 1843 credits the first double dahlia of the cream-scarlet series to be in that year. Both Schlechtendahl and Pepin reported obtaining a double form of D. coccinea. These are both believed to be in error; both Johann Sieckman and Christian Deegen of Kostritz, Germany published hand painted catalogs of numerous Show and Fancy dahlias of cream colors in 1840. Sieckman reported he had "developed these over the years 1829 to 1840”. Several of these are illustrated in the German Yearbook of 1990/91. It is quite likely that the double credited to D. coccinea was instead a variety of D. crocea, the 1804 introduction of what was subsequently, in 1907, renamed D. coronata. In 1851 Joseph Sieckmann of Kostritz, Germany announced "I have been developing the Lilliput dahlias for six to eight years and am proud that I have the jump on the rest of the world." Regel's Gartenflora of 1852 shows a drawing of six dahlias of the same form as the Show and Fancy types but considerably smaller in size identified as Lilliput dahlias. It also shows one of dark red and the others light blends of both color groups. The first of the series was not announced, so we can not determine the name of the original of these "miniature Show types, " but six varieties, ‘Lilliput Nelke’, ‘Deutscher Jungling’, ‘Deutsche Lilliput Rose’, ‘Alexandra Nicolaiewna’, ‘Lilliput Viole’, and ‘Weiner Leibing’ must share title to first of the series. When these diminutive dahlias were introduced into France these imaginative people compared them to the red tassels on the caps of the French sailors of the period and dubbed them "pompones”. In English speaking countries this name was anglicized to pompon, the name they carry to this day. Other dahlias originally considered lilliputs were called ball-flowered, rose-flowered, chrysanthemum-flowered, zinnia-flowered, fircone-flowered, pearl- flowered, scale-flowered, aster-flowered, and cellformed- flowered. All soon apparently dropped from classifications.

          For about 15 years the Show and Fancy dahlias achieved great popularity, perhaps because of their uniform and refined nature. However, probably for this same reason after 1860 that popularity almost completely disappeared. An anonymous report in the Gardener's Chronicle of 1862 states that florists feared the dahlia was destined to comparative obscurity. This was changed by the introduction of a new species into the hybrid mix.

          Cactus | example

          In 1872 J.T. Van der Berg of Utrecht, Holland received a shipment of seeds, plants etc. from a friend in Mexico. The entire shipment was badly rotted and appeared to be ruined. Van der Berg said he examined the shipment carefully and saved every thing that seemed to have any promise at all. He found one small piece of root that seemed alive. It was carefully planted and tended and did grow into a plant which he identified as a dahlia. He made cuttings from the plant during the winter of 1872-1873. This was an entirely different type flower of a rich red color and a high degree of doubling. Affourit called it Dahlia juarezii for, or in memory of Benito Pablo Juarez, the President of Mexico, who had died earlier in the year 1872. In 1874 he catalogued it, and offered it for sale, as "New imported variety from Mexico, very large rich crimson flowers splendid fiery orange scarlet, equal to the beautiful color of the red poppy. Its form is very outstanding and different in every respect of all known dahlia flowers, at a distance one should believe to see the flowers of the Cereus speciossissimus but than with fine pipe-formy, rolled up flower leaves.” Comparison to this Cereus, a genus of the cactus, resulted in the name “cactus” for this new dahlia, and the name remains with us today. Various authorities have since unsuccessfully searched for this plant in the wild; it is reported to be a semi-fertile natural hybrid of or variety of D. popenovii. In any event, this plant is considered to be the parent of all cactus-type dahlias.

          Single | example

          Single-flowered forms, including Collarette, Orchid, and Mignon Single types, originated with Dahlia coccinea crossed over time with probably only one or two other species. This early series of single types were called "simplex" and described as 2-3 inch blooms with rays relatively long, slender, acuminate (with a long tapering point) notched at the end, and with such wide spaces between the tips of the rays as to give the flower a stellate appearance on 2-3 foot bushes. Such a description is quite representative of a drawing made in the garden of a Mr. John Fraser in 1803. Later color plates of these early dahlias show somewhat broader and less pointed rays indicating a developmental improvement through the process of divergent variation. However all reported singles of those early days were described as scarlet, crimson or red. In 1843 D. crocea and possibly D. barkerae was added to the mix, and hybrids with it resulted in the colors normally associated with modern dahlia breeding. These hybrids resulted in larger plants and greater flower color and (especially) foliage variability than in previous exercises.

          Collarette | example

          The first Collarette ‘President Viger’ was raised in France by Gerard in 1900 and first exhibited in 1901. In 1903 single giant dahlias, some more than nine inches in diameter were introduced into France from Holland. In 1912, J.K. Alexander, a dahlia specialist in East Bridgewater, Massachusetts, succeeded in developing the first collarette dahlia of American origination. Suptitz of Germany also originated a type of collarette shortly after the French in the early 1900s. These had more pointed petals, some revolute as in ‘Leitstern’, or involute as in ‘Katchen Von Schwarzatal’. These apparently failed to catch on in other countries. However the Germans can be credited with supplying the name. They called them ‘Halskrausen’ (neckcollar) which derives from the 16 th century ruffled collars, so often shown in portraits from that time.

          Orchid | example

          The Orchid-flowered dahlias originated with the French. In 1919 L. Martin and Sons introduced a type of dahlia they called Stellar. One of the first varieties was named ‘Orchis’, which is the French word for “orchid”. In 1920 Wouters of Holland originated a nearly identical type of flower he called “clematis-flowered”. These appear to be the last true forms to be introduced. There is little literature about these dahlias in historical documents. In 1921 the Royal Horticultural Society published the first "Official Accepted Classification of Dahlias”. The Orchid-flowered dahlia was not listed. In 1925 the Classification was officially accepted by the American Dahlia Society in its Bulletin of April 1925. In 1927 Foerster and Schneider published a Classification of dahlias in Germany. That document was updated in 1933 by adding Class IVa: Orchid-flowered Dahlias, but did not include any cultivar names. In 1942 still another German publication, listed six cultivars as orchid-flowered. One of these was ‘Orchis’ and presumably the reason for class name. When the first Joint Classification Guide sponsored by the American Dahlia Society and the Central States Dahlia Society was issued in 1949 the Orchid-flowered dahlias were listed as a class.

           Mignon Single | example

          In 1873 Benedict Roezl introduced into Europe a deep orange colored single form which because of its petite and graceful form was given the descriptive species name “Dahlia gracilis”. It was so well received that it was the immediate cause of a reawakened interest in the single types. By 1880 numerous novelty forms of this dahlia had been introduced including ‘Mignon Stars’ and ‘Tom Thumb’. The first true Mignon dahlias were introduced by Dominicus of Rotterdam, Holland at about the same time and had slightly larger flowers that the original ‘Tom Thumb’ varieties. ‘Tom Thumb’ dahlias were developed by T.W. Girdlestone and introduced about 1880. These plants were quite dwarf, about 15 inches in height, while the early true Mignons were more like their parents in the 4-5 foot range. Hence these early Mignons were practically forgotten and the ‘Tom Thumb’ type promoted; these were eventually reclassified as the true Mignon. In about 1910-1920 Vervooren and Dominicus began developing smaller plants as well as blooms. One of the earliest was named ‘Red Riding Hood’. Perhaps the smallest dwarf ever produced, the plant never exceeded 5 inches in height even in the lush black, peaty soil of Holland.

          In 1921 when the Royal Horticultural Society established the first “Official Classification of Dahlias”, Mignon was described as not exceeding 18 inches in height, and in 1925 the American Dahlia Society adopted the classification as well. The designation was subsequently dropped by the RHS prior to 1961 and Mignon listed under the “singles” class. The Mignon remained as a classification in the US until 1963 when it was treated as a sub-class to the standard singles. In 1964 it was dropped from the ADS Classification Guide. When the current Class Number system was adopted in 1977 it was again reinstated, although the definition was changed to limit bloom size rather than plant size in the category.

          Anemone | example

          Dahlias with anemone-like flowers were first reported from Ireland 1n 1826. The first was grown by Mr. Drummond of Cork and brought to notice under the name ‘Bella Donna’. Pictured in Flora and Pomona, Plate 18 in 1829 shows it to have one or two outer rows of flat radiating rays with a distinctively different center area of many laciniated and involute, but not quilled petals. A flower named ‘Aegir’ was introduced in Germany in 1894, and seems to be generally considered the first true anemone-flowered dahlia. It is said to resemble D. excelsa. The principle resemblances are the partially tubulated center and the peduncle of the flowers as mentioned in the type description. From this it apparently was considered to have developed from D. excelsa. Interestingly, however, D. excelsa is considered a tree dahlia, 15-30 feet in height and blooms in mid-winter to spring in the Northern Hemisphere.

          G. Wouters of Leiden, Holland introduced a new type flower named ‘Ada Finch’ in 1917, and called “clematis-flowered”. It appears to not have caught on as an exhibition dahlia, due to a 1932 ruling by the Metropolitan Dahlia Society if England that anemone forms were not eligible for prizes. However, the plant remained in European gardens for at least several years. After the Anemone-flowered dahlias were established as a class it was reclassified with this group and continued to be reported until about 1940.

          In 1952 the paragon of all anemone-flowered dahlias was introduced by the Van Oostens Garden of Hillegom, Holland with the name of ‘Comet’. This bright red flower, with two or three rows of radiating petals tending to recurve surrounding an immense center disc of long almost totally quilled florets, has dominated the anemone-flowered class of dahlias throughout the world for the past fifty years. Characteristics of ‘Comet’ suggest it is highly probable that the modern anemone-flowered dahlias of that type have developed from variations of D. pinnata, D. crocea / D. coronata and D. juarezii.

          Paeony | example

          There have been several versions of the Paeony type of dahlias. The first of record were termed as a “sunflower” type six inches in diameter called ‘Will’s Sunflower’, described as an exceptionally beautiful, dark, scarlet-red variety with large semi-double blooms. It apparently looked very much as though it were a larger double-flowered form of D. coccinea with ray florets arranged as to resemble a double sunflower and not at all like the show and fancy types so popular a few years later. Of particular interest is that D. coccinea has not ever been found to naturally produce double flowers. In 1833 a dark red fully double Formal Decorative named ‘Turban’ was reported. A colored illustration of this dahlia appeared in the 1833 issue of the same series of publications. Another colored illustration in the same volume shows the variety ‘Aurantiaca Magnifica’, an almost fully double bloom of a scarlet color. Each of these was in their turn referred to as Paeony dahlias. Like most other novelty dahlias these apparently received little recognition by growers of the day and likely were rejected by the Metropolitan Dahlia Society dicta in 1832.

          Further developments of the paeony line were relatively slow to proceed. In 1884 Revoire of Lyon, France introduced the first all black foliage dahlia under the name ‘Lucifer’. This dark foliage has figured prominently in the modern Paeony- lowered dahlias. The next versions were reported by M.H. Hornsveld of Baarn, Holland about 1900 and said to be intermediate between decorative and single types. They too were referred to as Paeony dahlias by other growers of the day. Between 1900 and 1903 he exhibited them at the shows throughout Europe, and within the next 10 years had introduced a total of about 20 varieties. Kelway's Manual of Horticulture for 1909-1910 lists 35 Paeony dahlias and pictures one by the name of ‘H. Hornsveld’. It shows a large flower Salmon in color, with the typical brown or dark purple center disc and with two to three rows of petals. In 1923 Emile Nagels of Belgium began cross-breeding ‘Lucifer’ with a Decorative type called ‘Lemur’ in an attempt to develop a double dahlia with dark foliage. In 1927 he released ‘Congo Belge’, a red dahlia that met the definition of the new Paeony-flowered class adopted by the Royal Horticultural Society in 1921. Between 1930 and 1939 he introduced an additional 19 varieties all with the dark foliage of ‘Lucifer’.

          At about the same time (1927) Stephen Treseder of Cardiff, Wales introduced a dark Red Paeony type also with dark foliage and disc called ‘Bishop Hughes’. It is reported the namesake preferred the name be changed, and consequently it was next called ‘The Bishop’. However, modern rules of nomenclature forbade (and still forbids) use of articles in cultivar names. Consequently it was again renamed to simply ‘Bishop of Llandaff’. The plant ostensibly originated with Nagels in Holland; it definitely had the characteristic dark foliage. Until 1960 this dahlia had the Paeony class almost completely to itself, although other dahlias with the Paeony classification now and then showed up at shows; also-rans apparently soon dropped out of the picture. This appears to be the last of the true Paeony types. Several Paeony types have been reported but have generally been reclassified, determined to be in error or simply dropped out of circulation.

          Water Lily (Nymphaea) | example

          Although flowers of this type have been reported since 1828, they have generally been received with little favor. There has been two considerably different forms sharing this name for many years. In 1828, the first types were classified as “double camellia-flowered” with six inch diameter blooms. They were not received with favor at first and were not grown generally outside of Germany until after 1880. In 1890 L.K. Peacock discovered a somewhat similar form of Formal Decorative dahlia in a rural garden in New Jersey. In 1893 he introduced it as a Nymphaea dahlia. This would be the first time that name (the scientific name of Water Lilies) was used in connection with dahlias. In the 1921 Royal Horticultural Society's first "Official Classification of Dahlias" these were listed as "camellia-flowered dahlias” and described as “fully double; petals arranged regularly, petal edges a bit involute so they look like widely open tubes”. The doyen originated in 1919 by Schone of Leipzig, Germany, was called ‘Aureole’, and in 1933 a German classification included two new classes: Hybrid Cactus (later to be known as Semi-Cactus) and Decorative Dahlias, Subclass VIId, Nymphaea-flowered Dahlias. Although they gave no description, twenty one cultivars were listed under that class, including ‘Aureole’. All identifiable cultivars had previously been considered “camellia-flowered”.

          Sometime subsequent to the acceptance of the RHS Classification, both the RHS and the ADS apparently discontinued the use of the term “camellia-flowered”. Neither the RHS or ADS would again recognize this type of flower until 1964. In that year the ADS included the designation “Water Lily” as a sub-type of the Formal Decoratives but with no description. In 1977 the Water Lily form received recognition as a class by itself and described as "fully double flowers characterized by large, broad, and generally rather sparse ray florets which are straight or slightly incurved giving the flower a flat appearance, the depth being no more than half the diameter of the flower head." Neither the RHS or the ADS have ever officially recognized the classification Nymphaea although it has been and still is used in several countries.

A detailed timeline of important dates in Dahlia cultivation and hybridization
Dahlia History (.doc)