Open-centered flowers, with only 1 row of ray florets, with the margins flat or nearly so, regardless of the number of florets.

Open centered flowers with one row of ray florets surrounding a disc similar to single flowering types. The florets involute for two-thirds or more of their length. Usually partially overlapping.

Open centered flowers, with 1 or more rows of ray florets regardless of form or number of the florets, with the tubular disc-florets elongated, forming a pincushion effect.

Open-centered flowers, with only 1 row of ray florets, with the addition of 1 or more rows of petaloids, usually of a different color, forming a collar around the disc.

Open-centered flowers with 2-5 rows of ray florets with or without the addition of smaller curled or twisted floral rays around the disc.

"Cactus" Dahlias originated from the species, Dahlia juarezi and were originally from Mexico. Their names comes from the fact that their petals are curved similar to the foliage of many cacti.

Incurved Cactus Dahlias: Fully double flowers, with the margins of the majority of the floral rays fully revolute for 1/2 or more of their length and the tips of the rays curving toward the center (involute) of the flower. Petals rolled or tubular for their full length, with tips of the petals curving toward the center of the flower.
 

Straight Cactus Dahlias: Fully double flowers, with the margins of the majority of the floral rays fully revolute for their length or more, the rays being straight, slightly incurved or recurved. Petals rolled for one-half their length, straight or nearly straight.

Semi-Cactus Dahlias: Fully double flowers, with the margins of the majority of the floral rays fully revolute for less than half their length and the rays broad below. Petals flat at the base, with less than half of the petals rolled or quilled.

Fully double flowers, with the margins of the floral rays slightly or not at all revolute, the rays generally broad, either pointed or rounded at tips, with outer rays tending to recurve and central rays tending to be cupped and the majority of all floral rays in a regular arrangement. Flat petals with an even, regular placement throughout the flowers

Fully double flowers, with the margins of the majority of the floral rays slightly or not all revolute, the rays generally long, twisted or pointed and usually irregular in arrangement. Generally flat petals, sometimes slightly rolled at the tips, but with irregular arrangement of formation

Fully double flowers, ball-shaped or slightly flattened, floral rays blunt or round at tips and quilled or with margins involute for more than half the length of the ray in spiral arrangement, the flowers over 3 inches in diameter.

Fully double flowers, ball-shaped or slightly flattened at the face, the ray florets blunt, rounded, or indented. Involute for most of their length, fully involute for about one-half their length and normally displayed in a spiral arrangement.

Dahlias which normally produce flowers less than 4 inches in diameter excluding pompon types.

Tom Thumb Dahlias - This is a very dwarf race, the plants forming little bushes, but they generally do not bloom freely. The habit is compact, dense and the single flowers are borne well above the mass of leaves.

Having the same characteristics as Ball Dahlias but, for show purposes, not more than 3 inches in diameter

Fully double flowers almost round in shape with tightly quilled petals. Flower size 3 inches or less in diameter. It is the smallest dahlia flower type.

Closed center with multiple rows of ray florets normally broad and flat or slightly incurved, depth usually less that one half the diameter.

"Star" or "Cosmos Flowered" Dahlias - These are medium size plants with single or semidouble flowers and produce many flowers.

Decorative shaped flowers with petals being creased causing them to be narrow and involute with a slight recurve to the stem.