Paeonia (peony or paeony) is a genus of flowering plants, the only genus in the family Paeoniaceae. They are native to Asia, Southern Europe and Western North America. Boundaries between species are not clear and estimates of the number of species range from 25  to 40.
Most are herbaceous perennial plants 0.5 to 1.5 metres (1.5 to 5 feet) tall, but some resemble trees 1.5–3 m (5–10 ft) tall. They have compound, deeply lobed leaves and large, often fragrant, flowers, ranging from red to white or yellow, in late spring and early summer.
The peony is named after Paeon (also spelled Paean), a student of Asclepius, the Greek god of medicine and healing. Asclepius became jealous of his pupil; Zeus saved Paeon from the wrath of Asclepius by turning him into the peony flower.
The family name "Paeoniaceae" was first used by Friedrich K.L. Rudolphi in 1830, following a suggestion by Friedrich Gottlieb Bartling that same year. The family had been given other names a few years earlier. The composition of the family has varied, but it has always consisted of Paeonia and one or more genera that are now placed in Ranunculales. It has been widely believed that Paeonia is closest to Glaucidium, and this idea has been followed in some recent works. Molecular phylogenetic studies, however, have demonstrated conclusively that Glaucidium belongs in Ranunculaceae, but that Paeonia belongs in the unrelated order Saxifragales.
Peonies can be classified by both plant growth habit and flower type. Plant growth types are Herbaceous (nonwoody), Tree (shrub), and Itoh (or "Intersectional"), which is intermediate between herbaceous and tree forms. In winter herbaceous peonies die back to their underground parts, whereas tree peonies lose their leaves but retain viable woody stems above ground. The Itoh hybrids are intermediate between herbaceous and tree forms. They are named after Toichi Itoh, who first produced a successful intersectional hybrid in 1948.
The following sequence of flower types becomes more complex in its arrangement of petals. The flower types include Single (e.g., Athena, Scarlet O’Hara), Japanese (Nippon Beauty, Madame Butterfly), Anemone, Semi-Double (Paula Fay, Buckeye Belle), Double (Gardenia, Paul M. Wild) and Bomb-Double (Raspberry Sundae, Mons Jules Elie).
Chemistry and biological activities 
Over 262 compounds have been obtained so far from the plants of Paeoniaceae. These include monoterpenoid glucosides, flavonoids, tannins, stilbenoids, triterpenoids and steroids, paeonols, and phenols.
Biological activities include antioxidant, antitumor, antipathogenic, immune-system-modulation activities, cardiovascular-system-protective activities and central-nervous-system activities.
The herb known as Paeonia, in particular the root of P. lactiflora (Bai Shao, Radix Paeoniae Lactiflorae), has been used frequently in traditional medicines of Korea, China and Japan. Research suggests that constituents in P. lactiflora – paeoniflorin and paeonol – can modulate IgE-induced scratching behaviors and mast cell degranulation.
Herbaceous and Itoh peonies are propagated by root division, and sometimes by seed. Tree peonies can be propagated by grafting, division, seed, and from cuttings, although root grafting is most common commercially.
- Herbaceous species (about 30 species)
- Paeonia abchasica
- Paeonia anomala
- Paeonia bakeri
- Paeonia broteri
- Paeonia brownii (Brown's peony)
- Paeonia californica (California peony)
- Paeonia cambessedesii (Majorcan peony)
- Paeonia caucasica
- Paeonia clusii
- Paeonia coriacea
- Paeonia daurica
- Paeonia emodi
- Paeonia hirsuta
- Paeonia intermedia
- Paeonia japonica (Japanese peony)
- Paeonia kesrouanensis (Keserwan peony)
- Paeonia lactiflora (Chinese peony)
- Paeonia macrophylla
- Paeonia mairei
- Paeonia mascula (Balkan peony)
- Paeonia mlokosewitschii (golden peony)
- Paeonia obovata
- Paeonia officinalis (European peony, type species)
- Paeonia parnassica (Greek peony)
- Paeonia peregrina
- Paeonia rhodia
- Paeonia sinjiangensis
- Paeonia sterniana
- Paeonia steveniana
- Paeonia tenuifolia
- Paeonia tomentosa
- Paeonia veitchii (Veitch's peony)
- Paeonia wittmanniana
- Woody species (about 8 species)
- Paeonia decomposita
- Paeonia delavayi (Delavay's tree peony)
- Paeonia jishanensis (syn. P. spontanea; Jishan peony)
- Paeonia ludlowii (Ludlow's tree peony)
- Paeonia ostii (Osti's peony)
- Paeonia qiui (Qiu's peony)
- Paeonia rockii (syn. P. suffruticosa subsp. rockii; Rock's peony or tree peony)
- Paeonia suffruticosa (Chinese tree peony)
Symbolism and uses 
The peony is among the longest-used flowers in Eastern culture and is one of the smallest living creature national emblems in China. Along with the plum blossom, it is a traditional floral symbol of China, where the Paeonia suffruticosa is called 牡丹 (mǔdān). It is also known as 富贵花 (fùguìhuā) "flower of riches and honour" or 花王 (huawang) "king of the flowers", and is used symbolically in Chinese art. In 1903, the Qing Dynasty declared the peony as the national flower. Currently, the Republic of China on Taiwan designates the plum blossom as the national flower, while the People's Republic of China has no legally designated national flower. In 1994, the peony was proposed as the national flower after a nationwide poll, but the National People's Congress failed to ratify the selection. In 2003, another selection process has begun, but to date, no choice has been made.
The ancient Chinese city Luoyang has a reputation as a cultivation centre for the peonies. Throughout Chinese history, peonies in Luoyang have been said to be the finest in the country. Dozens of peony exhibitions and shows are still held there annually.
In Japan, Paeonia lactiflora used to be called ebisugusuri ("foreign medicine"). Pronunciation of 牡丹 (peony) in Japan is "botan." In kampo (the Japanese adaptation of Chinese medicine), its root was used as a treatment for convulsions. It is also cultivated as a garden plant. In Japan Paeonia suffruticosa is called the "King of Flowers" and Paeonia lactiflora is called the "Prime Minister of Flowers."
In 1957, the Indiana General Assembly passed a law to make the peony the state flower of Indiana, a title which it holds to this day. It replaced the zinnia, which had been the state flower since 1931.
Mischievous nymphs were said to hide in the petals of the Peony, giving it the meaning of Shame or Bashfulness in the Language of Flowers. While the peony takes several years to re-establish itself when moved, it blooms annually for decades once it has done so.
Peonies are also extensively grown as ornamental plants for their very large, often scented flowers.
Peonies are a common subject in tattoos, often used along with koi-fish. The popular use of peonies in Japanese tattoo was inspired by the ukiyo-e artist Utagawa Kuniyoshi's illustrations of the Suikoden, a serialized novel from China. His paintings of warrior-heroes covered in pictorial tattoos included lions, tigers, dragons, koi fish, and peonies, among other symbols. The peony became a masculine motif, associated with a devil-may-care attitude and disregard for consequence.
A cultivar of Paeonia lactiflora
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- Family and Suprafamilial Names At: James L. Reveal
- Shuguang Jian et alii on phylogeny of Saxifragales doi:10.1080/10635150801888871
- Paeoniaceae in Topwalks
- Germplasm Resources Information Network: Paeonia
- Flora Europaea: Paeonia
- Ornamental Plants from Russia: Paeonia
- The Peony Society (UK)
- Canadian Peony Society
- U.S. Peony Society
- Carsten Burkhardt's Open Source Peony Project
- German Peony Group
- China Daily article on the 2003 national flower selection process
- Rockii Tree Peony
- Paeonia mascula in the National Park of Alta Murgia, Apulia - Southern Italy