Understanding Dahlia Forms and Classifications

There are currently over 20,000 recognized varieties of Dahlias. Given the large variety of shapes, sizes and types, a Dahlia classification system was developed to better organize the flowers. At the present, the American Dahlia Society, and other worldwide societies recognize 19 different forms. To correctly recognize the differences between the forms, it is important to have a good understanding of various terms and definitions as they relate to Dahlias.
  • Ray Floret
    For practical purposes, the term floret is used interchangeably with a flower petal. Dahlia flowers are typically comprised of many florets.

  • Disc
    In some Dahlia forms, notably Orchid Flowering and Singles, there exists a central part of the flower head called the disc. A good example of a disc is the central part of a daisy. The disc is comprised of a large number of small, tubular florets.

  • Collar
    The small inner ring of petals, or florets surrounding the central disc.

  • Involute
    The way a dahlia ray floret, or petal, curls along its length is fundamental to the way dahlias are classified. Two terms are used to describe this petal curl. they are Involute and Revolute. Petals that are involute curl inwards towards the center of the flower. Examine the graphic above. An involute petal will be curled upwards, towards the face of the flower or towards the sky.

  • Revolute
    The way a dahlia ray floret, or petal, curls along its length is fundamental to the way dahlias are classified. Two terms are used to describe this petal curl. they are Involute and Revolute. Revolute petals are effectively the opposite of involute. Revolute petals curl outwards down their length away from the center of the flower. They curl down, towards the stem of the plant or towards the ground.

  • Incurved
    Bent or curved inwards or forwards towards the front of the flower.

  • Recurved
    Curved downward or backward toward the flower stem.

    The Dahlia forms and classifications as they are currently recognized are identified below.

  • Formal Decorative (FD)
    Formal decorative Dahlias have relatively broad, flat ray florets with edges partially rolling back (revolute) or forward (involute). Ray florets are uniform and regularly arranged and tend to curve towards the stem of the plant (recurved). Flowers have no visible central disc and are fully double.
    View our catalog of Formal Decorative Dahlias.
    Informal Decorative (ID)
    Informal Decorative Dahlias have ray florets that are twisted, curled or wavy creating the overall effect that the petals are not flat. Ray florets exhibit somewhat random or irregular placement. Petals may be partially rolled back (revolute).
    View our catalog of Informal Decorative Dahlias.
    Cactus (C)
    Straight Cactus, or simply Cactus Dahlias, have fully double flowers with long, pointed ray florets. These may be either straight or may curve back towards the stem (recurved). Ray florets are rolled back (revolute) for more than 50% of their length and radiate in all directions from the center of the flower.
    View our catalog of Cactus Dahlias.
    Semi Cactus (SC)
    Semi Cactus Dahlias have fully double flower heads with pointed ray florets that are usually broader at the base than those of the cactus dahlia. Ray florets may be straight, incurved (Up, or towards the front of the flower) or recurved (towards the stem of the flower). Ray florets must be rolled back (revolute) for less than 50% of their length.
    View our catalog of Semi Cactus Dahlias.
    Incurved Cactus (IC)
    Incurved Cactus Dahlias have fully double flowers with pointed ray florets that are curve towards the front or center of the flower head (incurved). Individual ray florets are rolled back (revolute) for more than 50% of their length.
    View our catalog of Incurved Cactus Dahlias.
    Laciniated (L)
    Laciniated Dahlias have ray florets whose tips are split or laciniated. The length of the split should be in proportion to the length of the ray floret. There is an overall twisting in the area of the split creating an overall fringed effect. Ray florets may be either involute (rolled forward) or revolute (rolled back).
    View our catalog of Laciniated Dahlias.
    Ball (BA)
    Ball dahlias have fully double flowers, rounded or ball shaped and may be slightly flattened at the face. They must be 3.5 inches in diameter or greater. Ray florets are spirally arranged and either blunt, rounded or indented at the tips. Individual ray florets are fully involute (rolled up or forward) for up to 50% of their length, but partially involute for most of their length. View our catalog of Ball Dahlias.
    Mini Ball (MB)
    Miniature Ball dahlias are similar to Ball dahlias but are smaller, ranging in size from over 2 inches to 3.5 inches in diameter. They have fully double flowers that are rounded or ball shaped and again may be slightly flattened at the face. Ray florets are spirally arranged and are involute for most of their length but fully involute for up to 50% of their length.
    View our catalog of Mini Ball Dahlias.
    Pompon (P)
    Pompon dahlias have fully double flowers similar to the Ball and Mini Ball but are smaller. In fact, at less than 2 inches in diameter, they are the smallest of the dahlia forms. They are also more globular or spherical in shape. Ray florets are involute for their entire length and fully involute for at least 50% of their length.
    View our catalog of Pompon Dahlias.
    Stellar (ST)
    Stellar dahlias have fully double blooms with the depth, or thickness of the flower being between 50-66% of the diameter of the bloom. The ray florets gradually evolve from the more central immature florets to the fully developed outer ones. Both immature and fully developed Ray florets are narrow, partially involute (rolled up or forward) and feature a curve back towards the stem (recurved).
    View our catalog of Stellar Dahlias.
    Waterlily (WL)
    Waterlily dahlias have fully double and symmetrical blooms. The flowers are open faced and feature a delicate appearance. From the side, flowers should flat or saucer shaped. The center of the bloom should be closed and dome shaped breaking gradually to 4-7 rows of broad, flat or slightly cupped (involute), fully developed outer ray florets.
    View our catalog of Waterlily Dahlias.
    Peony (PE)
    Peony flowered dahlias resemble a double flower, but the central disc florets are visible. Surrounding the open center disc are two or more rows of surrounding ray florets. Those ray florets adjacent to the disc flowers may be smaller, twisted and or curled.
    View our catalog of Peony Dahlias.
    Anemone Flowering (AE)
    Anemone flowers are distinctive double flowers featuring a central, domed, pin cushion-like set of elongated tubular disc florets surrounded by one or more rings or rows of flattened ray florets.
    View our catalog of Anemone Flowered Dahlias.
    Collarette (CO)
    Collarettes are open faced dahlias with a visible central disc flower surrounded by a single row of flat, uniformly spaced ray florets. the ray florets may or may not overlap. Between the central disc and the ray florets is an inner ring, or collar, of small petaloids (half petals). These petaloids may be up to 50% of the length of the outer ray florets.
    View our catalog of Collarette Dahlias.
    Mignon Single (MS)
    Mignon Single dahlias must be less than 2 inches in diameter and are often on shorter plants. Otherwise, they are similar to Single dahlias with their visible central disk and a single row of evenly or uniformly spaced ray florets.
    View our catalog of Mignon Single Dahlias.
    Orchid Flowering (O)
    Orchid flowering dahlias are open centered with a visible central disc. Surrounding the disc is a single row of evenly spaced ray florets in a flat plane. Individual ray florets must be involute (rolled forward) for at least 2/3 (66%) of their length and fully involute for at least 1/3 or 33% of their length. In their entirety, the ray florets should appear long and vaguely tubular.
    View our catalog of Orchid Flowering Dahlias.
    Novelty(N)
    The American Dahlia Society currently recognizes three different Novelty Classifications. They represent Dahlias which do not fit into other classifications.
    View our catalog of Novelty Dahlias.

    A special thanks goes out to the American Dahlia Society, the Colorado Dahlia society, the Fraser Valley Dahlia society and many others for providing information that enabled this article to come together.
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