The genus Paeonia encompasses some of the most sought-after flowering plants for temperate gardens, valued for their large, often fragrant blooms and perennial longevity. Correct identification is necessary for understanding specific care requirements, as different types have distinct needs for planting depth and winter preparation. Identification begins with observing the plant’s overall growth habit and structural features. The three primary groups of peonies—herbaceous, tree, and intersectional—are differentiated by their fundamental structure, providing the first step in the identification process.
Distinguishing the Three Main Types
The most fundamental way to identify a peony type is by observing its behavior during the dormant season. Herbaceous peonies, such as those derived from Paeonia lactiflora, are true perennials that die completely back to the ground each autumn. The above-ground stems are soft and non-woody, and their energy reserves are stored in large, fleshy root systems below the soil line. New growth in the spring emerges from reddish, dormant buds, often called “eyes,” which form directly on the crown of the root system.
Tree peonies, which belong to the Paeonia suffruticosa group, possess a drastically different growth habit, maintaining permanent, woody stems throughout the year. These plants function as small, deciduous shrubs, with the woody framework remaining above ground even after the leaves drop in the fall. Mature specimens can reach heights of four to seven feet, and new growth sprouts from scaly buds along the previous season’s woody stems.
Intersectional peonies, also known as Itoh peonies, represent a successful hybrid cross between the herbaceous and tree types. This hybridization results in a plant that combines the characteristics of both parents. Like an herbaceous peony, the intersectional type dies back to the ground in the winter, with its stems becoming semi-woody but not persisting above ground.
The defining feature of the intersectional type is its ability to produce the unique yellow colors and massive flowers previously exclusive to tree peonies, along with stronger stems that typically do not require staking. While they die back to the ground, new stems emerge from the crown, offering the winter hardiness of the herbaceous type coupled with the exotic flower characteristics of the woody type.
Identification by Vegetative Features
Peonies can be identified even when not in bloom by examining their vegetative structures, particularly the leaves and stems. The herbaceous peony is characterized by stems that are smooth and entirely soft, green, and succulent throughout the growing season until they naturally collapse with the first hard frost. Their leaves are typically deeply lobed and dark green, often forming a dense, handsome mound of foliage.
Tree peonies exhibit a distinct woody, shrub-like stem texture that feels rougher and is covered in bark, similar to a small tree branch. The leaves of the tree peony are often more deeply dissected than the herbaceous types, sometimes displaying a bronze or purple tint in autumn. The presence of dormant, pointed buds along these woody stems in the winter is a clear identifier for a tree peony.
Intersectional peonies display foliage that is often described as intermediate, having a leaf shape and texture that leans toward the tree peony parentage. Their leaves tend to be robust and remain attractive, sometimes displaying subtle color changes, well into the late fall. The stems of the intersectional type are stronger and more robust than those of herbaceous varieties, which helps them support their large blossoms without toppling.
Flower Morphology and Bloom Timing
The bloom itself provides detail for identification, allowing for the classification of specific cultivars. Peony flowers are categorized into several primary forms based on the arrangement and modification of their petals and stamens.
Peony Flower Forms
The simplest is the single form, which features one or two rows of broad outer petals, called guard petals, surrounding a prominent center of stamens and carpels. The semi-double displays multiple rows of guard petals with visible stamens interspersed among the petals. The double form is characterized by a dense, rounded ball of petals where stamens have been transformed into petal-like structures (petalodes), completely obscuring the reproductive parts. A variation is the bomb form, where a ring of guard petals surrounds a higher, dense puff of shorter, incurved petals in the center. The anemone form has one or more rows of guard petals encircling a center of thin, ribbon-like structures called staminodes, which are transformed stamens that lack anthers.
Bloom timing is an identification marker, as cultivars are classified by their bloom period.
Bloom Timing Classifications
Very Early
Early
Midseason
Late Midseason
Late
Very Late
Horticulturalists use these classifications to extend the peony season in a garden, with the entire procession lasting up to seven or eight weeks when various types are planted together. Early blooming varieties can begin weeks before the late-season Paeonia lactiflora cultivars finish their display. Intersectional peonies often bloom over an extended period of three to four weeks, sometimes producing multiple flushes of flowers, which significantly lengthens the garden display.
Separating Peonies from Look-Alikes
The visual similarity of a fully double peony bloom to other garden flowers can lead to misidentifications, but simple observations can help distinguish them. Large garden roses are frequently mistaken for peonies due to their ruffled, multi-layered appearance and similar color palette. The most obvious difference is the presence of sharp thorns on the stems of roses, a feature completely absent on any part of a peony plant.
Another common confusion is with camellias, which also produce large, layered, rounded blossoms, particularly those grown in warmer climates. Camellias are easily separated from peonies because they are evergreen shrubs with thick, glossy, leathery leaves that remain on the plant year-round. Peonies are deciduous, possessing softer, deeply lobed leaves that completely die back in the colder months.
Ranunculus, sometimes called Persian buttercups, can also resemble smaller peony blooms, especially in cut flower arrangements, due to their many layers of petals. However, ranunculus flowers are significantly smaller, typically only reaching a few inches in diameter. The overall plant structure is much more delicate and less woody than even an herbaceous peony, whose blooms are generally much larger, sometimes reaching a diameter of seven to ten inches on tree peony varieties.