https://americanpeonysociety.org/learn/herbaceous-peonies/flower-types-anatomy/
Peony Flower Types and Anatomy | American Peony Society
Peony flowers are astounding in size, shape, form and structure The flower forms of peonies are wide and varied. Each flower form presents intrigue, beauty and contemplation for the viewer. The American Peony Society’s official standard includes six forms – Single, Japanese, Anemone, Semi-double, Bomb and Full double.