Dahlia Types and their Classification
ACOLLECTION of dahlias is probably without equal among garden plants both for garden decoration and indoor flower arrangement. They can adapt themselves to a variety of soil and weather conditions, and the hybridists have developed a wide range of colours and forms.
The dahlia, named in honour of Dr. Andreas Dahl, a Swedish botanist and pupil of Linnaeus, originated in Mexico and was first introduced into the British Isles from Spain in about 1798. Many new varieties have recently been raised in England, Holland, Germany, America and Australia, and it is now a truly cosmopolitan flower.
The dahlias first introduced into the British Isles were wild species such ascoccinea, D. Imperialis, D. Merckii and D.juarezii. The latter is probably a hybrid of the D. variabilis type, into which class all the present-day varieties are grouped. Continuous crossing and selection between varieties, and originally between species, have resulted in the present large and exotic range of dahlias.
A classification of the various forms of dahlia has been adopted by the Royal Horticultural Society and the National Dahlia Society and, although there are a number of border-line cases, most new varieties fall quite readily into one of the classes, each of which has certain common characteristics. There are eleven distinct classes, which are decided on the basis of the shape and formation of flower and petal, and the size of the bloom. Some of the classes are sub-divided according to the size of their flowers.
CLASSIFICATION OF DAHLIAS
CLASS 1: SINGLE-FLOWERED DAHLIAS
Single blooms, up to 4 in. in diameter, having one row of smooth ray florets surrounding a central disk. This class is sub-divided into: (a) Show Singles, with round-ended, overlapping petals. (b) Singles, with more pointed petals which do not overlap as much.
CLASS 2: STAR-FLOWERED DAHLIAS
Small flowers, having two or three rows of pointed petals which overlap very slightly, are somewhat recurved at the edges and form a shallow cup-shaped flower round a central disk.
CLASS 3: ANEMONE-FLOWERED DAHLIAS
This class has an outer row of ray florets surrounding a central zone of comparatively long, tubular florets, which gives the flower an attractive, domed centre, often of a contrasting colour.
CLASS 4: COLLARETTE DAHLIAS
An unusual and brightly coloured class, with one or more rings of flat ray florets, and a ring or collar of smaller florets about half the length of the ray florets, usually contrasting in colour with both the ray florets and the disk.
CLASS 5: PAEONY-FLOWERED DAHLIAS
This class is sub-divided into three groups, all of which have two or three rows of broad and usually flat petals surrounding a central disk: (a) Large-flowered, diameter of flowers over 7 in. (b) Medium-flowered, diameter of flowers 5 to 7 in. (c) Small-flowered, diameter of flowers up to 5 in.
CLASS 6: DECORATIVE DAHLIAS
This class covers a wide range, from near pompon to near cactus forms. The fully double flowers have broad petals which are normally flat (though they are sometimes slightly twisted) and bluntly pointed or rounded at their flattened tips. This class is sub-divided into four groups: (a) Large-flowered, diameter over 8 in. (b) Medium-flowered, diameter 6 to S in. (c) Small-flowered, diameter 4 to 6 in. (d) Miniature, diameter up to 4 in.
CLASS 7: DOUBLE SHOW AND FANCY DAHLIAS
Fully double, very regular, almost globular flowers, 4 in. or more in diameter, the central florets being slightly smaller than the outer ones, with blunt mouths and incurved edges. The show types are self-coloured, and the fancy types are bi-coloured or variegated. It is one of the oldest classes, and some varieties are still popular in spite of their tendency to produce weak stems.
CLASS 8: POMPON DAHLIAS
This class has the same characteristics as Class7, except that the blooms are smaller and often more globular and are usually borne on strong stems. The class is subdivided into:
(a) Large-flowered, diameter 3 to 4 in.
(b) Medium-flowered, diameter 2 to 3 in.
(c) Small-flowered, diameter up to 2 in.
CLASS 9: CACTUS DAHLIAS
Cactus dahlias show no disk unless the weather is unfavourable or the blooms are old. The fully double flowers have straight or incurving petals which are partially revolute (inturned along their length), and tend to be narrow and pointed, which gives the flowers a star-like appearance. The tips of the petals of several new varieties are laciniated or split, thus giving the flowers an added lacy charm which makes them popular for flower arrangements. This class is subdivided into:
(a) Large-flowered, diameter over 8 in.
(b) Medium-flowered, diameter 6 to 8 in.
(c) Small-flowered, diameter 4 to 6 in.
(d) Miniature, diameter up to 4 in.
CLASS 10: MISCELLANEOUS
Several of the varieties in this class (types which do not fit easily into any other class) are also useful for flower arrangement, such as the double orchid-flowered Giraffe and the smaller-flowered Disneyland.
CLASS 11: DWARF BEDDING
The flower type in this section can be any of the foregoing ten classes. Good varieties are found in single, decorative, paeony-flowered, cactus and anemone-flowered forms, the common factor being that they do not usually exceed 24 in. in height and are therefore well suited for bedding purposes. A strain known as Topmix, recently introduced from Holland, carries small flowers of l to 2 in. in diameter on plants about 12 to 15 in. high.