Single Flower Form

One or more rows of large petals surround a band or row of natural, pollen bearing stamens, centered by a cluster of seed bearing structures, the carpels, usually topped by the natural, pollen-receiving stigma.

Japanese Flower Form

This form is similar to Singles except all of the stamens are transformed, also called "all-over transformation," into staminodes, petal-like segments which retain some of the yellow color of the pollen sacs but normally do not release pollen. For breeders, all-over transformation is inherited as a recessive.

Anemone Flower Form

Also similar to Singles and Japanese forms, except the stamen segments are further transformed into slender petals, called petalodes, often near the same hue as the guard petals. This form is less constant, inasmuch as lesser advancement of the center segments may result in near Japanese form staminodes. Greater advancement may result in larger center segments and a Bomb form. Exhibitions usually call for Anemone and Japanese forms to be judged together in the same classes.

Bomb Flower Form (Bomb Double)

Technically, the anatomy is the same as the singles, except the center petals, while smaller than the larger outer petals, have the same texture and color density.  Ideally, the center segments form a neatly tailored ball or mound, the "bomb," said to have been adopted from "bomb", the name of a molded frozen desert popular after World War I. The bomb is small as the flower bud first opens and grows dramatically larger as the flower matures. Rarely, a cultivar that has two stage-double anatomy but also forms a neatly tailored "bomb" is exhibited in this class, notably Mme de Verneville.

Semi-Double Flower Form

Also a flower-in-flower form, particularly in the Lactifloras, always having progressive stamen transformation, having a lesser quantity of inner petals and greater proportion of natural, pollen-bearing stamens. This results in a sufficiently large component of yellow stamens so that their yellow color is a prominent factor in the flower color. Oddly, perhaps, when a flower of this anatomy contains yellow staminodes instead of stamens, it may look similar, but does not meet the "pollen bearing stamens always prominent" condition of the Semi-Doubles classes. When an exhibition follows the rules, these end up a novelty in the Doubles classes.

Double Flower Form (Full Double)

This is the classic flower-in-flower peony form, sometimes described as "two-stage double," some actually triple-stage, resulting in the most massive of peony flowers. Some of these also have the "all-over" stamen transformation of the Bombs, where no stamens can be found in the depths of the flower. When the individual instead carries "progressive transformation" of the stamen segments, there will be a more or less thin circle of natural stamens seen defining the inner margin of each component flower. Only rarely will carpels useable for breeding be found in these more massive flowers. Traditionally, pollen bearing stamens, when their presence is obvious, have been "frowned upon" for the doubles show classes.