Peonies (Paeonia spp.) are available in about 30 species, but four species in particular are readily acquired and grown in gardens in temperate regions of the world. Many modern varieties have been developed by genetically crossing species, increasing the diversity in the colors available. In general, peonies need a cool to cold winter for dormancy each year and are best grown in U.S. Department of Agriculture hardiness zones 3 through 8.
The common peony (Paeonia officinalis) has origins in Europe and typically grows about 25 to 30 inches tall. Varieties are available in single and double flowers, which have extra petals to look full and fluffy. Single peony varieties display a central cluster of yellow stamens. Common peony flower colors range from deep red to pink to rose to white. Modern varieties are selected for more intense flower petal colors and some will reveal violet-pink, light purple, lavender and dark maroon-burgundy tones.
The Chinese peony (Paeonia lactiflora) is native to much of eastern Asia, not just China. Since these plants are also herbaceous and grow 20 to 28 inches tall, they tend to be grouped and are called common peonies by gardeners not enthralled by botanical taxonomy. The flowers are single or double, and the central core of stamens is pale yellow. Petals typical are white to pale pink and rose.
Not really "trees" but a species of peony that grows semiwoody stems that remain through the winter, tree peonies (Paeonia suffruticosa) are also called moutans. Plant breeders have crossed this species with Paeonia potaninii, another tree peony, to create a broader array of flower colors. Depending on variety, tree peony blossoms can be white or range from deep red to rosy pink and gold to canary yellow. Stamens in the flower centers are always a shade of yellow, and sometimes the lower bases of petals reveal a contrasting darker blotch of dark red, maroon or brown. Tree peonies typically grow 4 to 7 feet tall.
The fernleaf peony (Paeonia tenuifolia) bears frilly, lacy foliage that is attractive and topped by red flowers that have central clusters of yellow stamens. Plants grow about 24 inches tall.