Paeonia lactiflora, commonly known as the Chinese peony or common garden peony, is a herbaceous perennial species prized for its lush, often fragrant flowers. From a botanical perspective, its cultivars are primarily classified based on the morphology and arrangement of their floral organs—specifically the petals, stamens, and carpels. This results in several distinct flower forms, each with a unique genetic expression.
This form represents the most basic and wild-type flower structure. A single-form bloom consists of one or two whorls of broad, guard petals surrounding a central cluster of functional reproductive organs: numerous prominent stamens with pollen-bearing anthers and visible carpels (the female parts that develop into seed follicles). This form is highly attractive to pollinators like bees, as it provides easy access to nectar and pollen.
Botanically, the Japanese form is an intermediate stage between the single and double forms. The flower retains the single whorl of guard petals. However, the stamens have undergone a transformation; the filaments may widen, and the anthers become staminodial. These staminodes are petaloid structures that retain a filament-like base but develop a flattened, often colorful and decorative tip, which can be yellow, pink, or matching the guard petals. The functional carpels remain exposed and fertile in the center.
This form is often confused with the Japanese form but is distinct. The outer ring consists of standard guard petals. The center, however, is filled with a dense, pompom-like cluster of elongated, tubular staminodes. These staminodes are much more fully transformed into petal-like structures than in the Japanese form and are typically a different color, often white or yellow, creating a striking contrast. The true reproductive parts are often hidden within or are sterile.
As the name suggests, this form exhibits a transition towards doubling. The flower features multiple rows of petals interspersed with functional stamens, which may be scattered throughout the bloom or concentrated in patches. The central carpels are usually visible but may be partially obscured. This form displays a mix of reproductive function and ornamental showiness, with a looser, more layered appearance than the single forms.
The double form is characterized by the transformation of almost all stamens and sometimes even carpels into petals (petalody). This results in a large, densely packed bloom with no visible reproductive parts. Two main subtypes exist from a structural viewpoint. The Bomb type has a high, rounded central mass of petaloids ( transformed stamens) surrounded by broader guard petals, creating a globular shape. The Crown type displays a distinct tiered structure: an outer ring of guard petals, a middle ring of smaller, sometimes incurved petaloids, and a central crown or dome of even larger, erect petaloids.
Regardless of flower form, all Paeonia lactiflora cultivars share the same fundamental herbaceous plant structure. They form a clump of annual stems that emerge from subterranean buds on a woody crown each spring. After flowering, the foliage performs photosynthesis, building energy reserves in the roots before the stems die back completely to the ground in autumn. This cyclical growth habit is a key characteristic separating them from their woody relatives, the tree peonies.
