THE GROWING WORLD OF DAHLIAS

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DAHLIA TYPES

AND

INTERNATIONAL CLASSIFICATION OF DAHLIAS

The dahlia is a flower of many forms, the master of flower disguise and indeed continues to evolve with new developments around 2006.

In order to help identify the many varieties that have existed, attempts have been made to identify characteristics that would allow the flowers to be categorised. This process formed the basis for classification.

In the early days, most dahlias were species types and single flowered. They were mainly grown by botanists in Europe who identified them by their species names.

Eventually hybrids appeared to give rise to Dahlia variabilis, and this began to give rise to identification problems as some flowers now had several rows of "petals". As a member of the Compositae, the dahlia flower is comprised of disc and ray florets, each a flower in its own right, although most horticulturists describe them as petals of the dahlia flower. Once double and semi double forms appeared, other breaks in formation also arose including the pompon type (like the pompon on the top of a sailor's hat) and the collerette type.

By 1900, a few different types were recognised, based on overall shape or colour. Cactus, pompon, single, show and fancy were included in an NDS Guide of varieties in 1904.

During the 1900's more types appeared and by 1950, provisional classifications were possible, but these differed from country to country.

In 1962, at the International Horticultural Congress in Brussels and subsequently at the Congress in Maryland in 1966 an international group of botanists and dahlia lovers (supported by the British, Dutch and American Dahlia Societies) got together to find a way of classifying dahlias in a way that was acceptable to all, and would last for all time.. In order to do this, major and minor characteristics were identified, and classification became a relatively simple matter. This was published in 1969 by the RHS, who had been appointed as the International Registration Authority for Dahlias. To this day, the International Registrar holds a list of all registered dahlias along with much information about them, and in 2003 it holds some 18000 different cultivars.

So what were the major botanical characteristics they defined?

Issues of colour and size were discounted as these could be arbitrary and open to individual interpretation as well as differing growing conditions and climates, and shape was seen to be the defining characteristic. It was essential that a flowchart or decision table of the classifying characteristics be developed so it was not open to interpretation and thus a firm basis for the classification process was found.

Firstly, is the central disk visible (open centred), or is the flower fully double (ie only ray florets visible at the centre). In the case of open centred, the overall appearance of the bloom was then considered.

Secondly in the case of fully double blooms, the folding of the individual ray florets along their longitudinal axis was considered. It could be flat, involute (ie curling inwards) or revolute (ie curling backwards), or even a mixture of these.

As a minor characteristic, the end of any ray floret may be split into two or more divisions. This characteristic was defined as Fimbriation of the petals, and once a flower is put into the appropriate group, the bloom may be sub-defined on this minor character.

The outcome of the discussions was a classification table that had nine clearly defined groups, and a tenth group to incorporate any varieties that did not fit the characteristics of any of the other nine groups. Many of these groups were sub-divided into a set of diameter sizes which were purely arbitrary, but were essentially <4" for Miniature, <6" for Small, <8" for Medium, <10" for Large, and >10" for Giants.

CLASSIFICATION GROUPS

GROUP 1 - SINGLE FLOWERED DAHLIAS.

These have a single ring of ray florets (petals) which may overlap surrounding the central disc. The petals may have rounded or pointed ends.

GROUP 2 - ANEMONE FLOWERED DAHLIAS.

The central disc florets are elongated with tubes that form a dense group and show no disc. There are one or more rings of generally flattened ray florets.

GROUP 3 - COLLERETTE DAHLIAS.

These have a single outer ring of generally flat ray florets, which may overlay, with a ring of small florets (the collar), the centre forming a disc.

GROUP 4 - PAEONY FLOWERED DAHLIAS.

These have two or more rings of generally flattened florets, the centre forming a disc.

GROUP 5 - DECORATIVE DAHLIAS

Decorative dahlias have fully double blooms showing no disc.

The ray florets are broad, scarcely revolute or involute along their length (longitudinal axis), generally flat or slightly twisted and usually bluntly pointed

GROUP 6 - BALL DAHLIAS

Ball Dahlias have fully double blooms, ball shaped or slightly flattened. The ray florets blunt or rounded at the tips, with margins spirally arranged and involute for more than half the length of the florets.

GROUP 7 - POMPON DAHLIAS

Pompon Dahlias have blooms similar to that of Ball Dahlias, but more globular and of miniature size (not exceeding 2 inches (51mm) in diameter for exhibition) with florets involute for the whole of their length (longitudinal axis).

GROUP 8 - CACTUS DAHLIAS

Cactus Dahlias have fully double blooms, the ray florets are usually pointed, the majority narrow and revolute for more than half their length (longitudinal axis) and either straight or incurving.

GROUP 9 - SEMI-CACTUS DAHLIAS

Semi-Cactus Dahlias have fully double blooms. The ray florets are usually pointed, the majority narrower than those of Decorative Dahlias, but broader than those of Cactus Dahlias, and revolute for half their length (longitudinal axis) or less, broad at the base, and either straight or incurving.

GROUP 10 - MISCELLANEOUS DAHLIAS

Any Dahlias that do not fall into one of the foregoing groups, eg Orchid Flowering dahlias (flowers as in Single Dahlias excepting that the rays are involute, their margins meeting or overlapping for at least two thirds of their length from tip towards base), etc.

Minor Characteristics

A fimbriated type is one where the ends of the petal are split into two or more divisions.

Dwarf bedding dahlias which do not usually exceed 609 mm. (24in.) in height.

Liliput dahlias are of exceptionally short growth habit, do not usually exceed 304 mm. (12in.) in height.

A waterlily type is a decorative dahlia that has cupped petals and is very shallow in depth due to the presence of less rings of petals than in fully developed decoratives.

COLOURS.

Having determined a classification by shape, an attempt was then made to classify by colour to obtain uniformity of definition around the world.

COLOUR CLASSIFICATION

For the purpose of Colour Classification, all colours, shades, tints hues and combinations thereof found in the cultivated forms of the dahlia have been grouped in the following thirteen classes.

Colour Classification is determined by the predominant colour or colours which appear on the face of the ray florets and in such classification the colour of the reverse of the ray florets is not generally taken into consideration. An exception is made in the case of certain orchid-flowered, pompon or ball dahlias.

In the case of Blended, Bicolours or Variegated varieties the first colour indicated is the dominant colour.

COLOUR DIVISION OF DAHLIAS

The agreed abbreviation follows the colour.

WHITE. (W.) Includes pale cream, ivory and colours that are nearly white or cream.

YELLOW. (Y.) All shades of yellow including dresden, primrose, sulphur, mimosa, straw, lemon, amber yellow, chrome yellow (light) and maize

ORANGE. (O.) All shades of orange including saffron, cadmium, apricot, tangerine and Indian orange.

FLAME. (Fl.) Includes spectral blends, xanthic in origin, of scarlet red or orange with yellow including saturn red, mars orange, nasturtium, fire red and poppy red.

BRONZE. (Br.) Includes buff, yellow ochre, majolica yellow, spanish orange, ochraceous orange, tan, zinc orange, terracotta, burnt orange, cinnamon and greyed suffusions and blends of such tones with pink and lavender.

RED (R.) Includes all shades of red from mandarin red to scarlet and crimson and also is to include cherry, claret rose, currant red, vermilion and carmine.

DARK RED. (Dk.R.) Includes cardinal, ox blood, and chrysanthemum crimson.

LIGHT PINK (Lt.Pk.) includes pale tints of orange-red and scarlets including salmon, peach, orient pink, shell pink, azalea pink, coral pink, venetian pink, french rose, porcelain rose, delft rose and empire rose.

DARK PINK. (Dk.Pk.) Includes tints and pinks of bluish tones including carmine rose, camellia rose, dawn pink, neyron rose, tyrian rose pink, china rose, phlox pink, spinel pink, rose pink, rhodamine pink and fuchsine pink.

LILAC, LAVENDER OR MAUVE. (L.) Includes all light tints of magenta, purple and violet and to include mauve, heliotrope, lilac and lavender.

PURPLES, WINES OR VIOLETS. (Pu.) Includes solferino purple, indian lake, magenta, magenta rose, ruby red, garnet lake, purple madder, paeony purple, dianthus purple, beetroot purple, maroon, petunia purple, imperial purple, royal purple, amethyst violet and violet.

BLENDS. (Bls.) Varieties in which two or more colours are intermingled and gradually merge into each other and are not provided for above.

BICOLOURED. (Bic.) Varieties in which the ground colour is tipped with another colour.

VARIEGATED. (Var.) Varieties in which the ground colour is striped or splashed with another colour.