They are native to Asia, Europe and Western North America. The current consensus is 33 known species. The relationships between the species need to be further clarified.
Most are floral perennial plants 0.25– 1 metre (1– 3 ft) high, yet some are woody hedges 0.25– 3.5 metres (1– 11 ft) tall. They have compound, deeply lobed leaves as well as big, frequently aromatic flowers, in colors ranging from purple as well as pink to red, white or yellow, in late spring and very early summertime. The blossoms have a brief flowering season, generally only 7– 10 days.
Peonies are amongst one of the most popular garden plants in temperate regions. Floral peonies are likewise offered as cut flowers widespread, although normally just readily available in late springtime as well as very early summer.  An emerging source of peonies in mid to late summertime is the Alaskan market. One-of-a-kind expanding problems because of lengthy hours of sunlight produce availability from Alaska when various other resources have actually finished harvest
All Paeoniaceae are deciduous perennial natural herbs or shrubs, with thick storage space roots as well as thin favor collecting water as well as minerals. Some varieties are caespitose (tufted), since the crown generates adventitious buds, while others have stolons. They have rather huge compound leaves without glands and also stipules, and also with anomocytic stomata. In the woody species the new growth arises from scaly buds on the previous flush or from the crown of the rootstock.
The huge bisexual blossoms are mainly single at the end of the stem. In P. emodi, P. lactiflora, P. veitchii and a lot of the cultivars these contributed to, couple of additional blossoms establish in the axils of the leaves. Flowers close at night or when the skies is overcast. Each flower is subtended by a variety of bracts, that may form a type of involucre, has 3-7 challenging complimentary sepals and also mostly 5-8, yet sometimes approximately 13 complimentary petals.
These categories however are intergrading, making it hard to appoint a few of them, as well as the number of these parts may vary. Within are numerous (50– 160) complimentary stamens, with anthers fixed at their base to the filaments, as well as are sagittate in shape, open with longitudal slits at the outer side as well as cost-free plant pollen grains which have three slits or pores and include two cells.
Within the circle of stamens is a basically noticeable, lobed disc, which is presumed not to excrete nectar. Within the disk is a differing number (1-15) of different carpels, which have a very short style and also a decurrent stigma. Each of these becomes a dry fruit (which is called a roots), which opens with a lengthwise suture and each of which includes one or a few large fleshy seeds. The annual growth is determined: if the expanding suggestion of a shoot is removed, no new buds will develop that season
About half of the species of the section Paeonia however is tetraploid (4n= 20), particularly many of those in the Mediterranean region. Both autotetraploids and allotetraploids are known, and some diploid species are also of hybrid origin.
The section Onaepia only includes P. brownii and P. californicum. The section Moutan is divided into P. delavayi and P. ludlowii, together making up the subsection Delavayanae, and P. catayana, P. decomposita, P. jishanensis, P. osti, P. qiui and P. rockii which constitute the subsection Vaginatae. P. suffruticosa is a cultivated hybrid swarm, not a naturally occurring species.
The remainder of the species belongs to the section Paeonia, which is characterised by a complicated reticulate evolution. Only about half of the (sub) species is diploid, the other half tetraploid, while some species both have diploid and tetraploid populations.
In addition to the tetraploids, are some diploid species also likely the result of hybridisation, or nothospecies. Known diploid taxa in the Paeonia-section are P. anomala, P. lactiflora, P. veitchii, P. tenuifolia, P. emodi, P. broteri, P. cambedessedesii, P. clusii, P. rhodia, P. daurica subsps. coriifolia, macrophylla, daurica and mlokosewitschii. Tetraploid taxa are P.
arietina, P. officinalis, P. parnassica, P. banatica, P. russi, P. peregrina, P. coriacea, P. mascula subsps. hellenica and mascula, and P. daurica subsps. tomentosa and wittmanniana. Species that have both diploid and tetraploid populations include P. clusii, P. mairei and P. obovata. P. anomala was proven to be a hybrid of P. lactiflora and P. veitchii, although being a diploid with 10 chromosomes. P. emodi and P. sterniana are diploid hybrids of P. lactiflora and P. veitchii too, and radically different in appearance. P. russi is the tetraploid hybrid of diploid P. lactiflora and P. mairei, while P. cambedessedesii is the diploid hybrid of P.
lactiflora, likely P. mairei, but possibly also P. obovata. P. peregrina is the tetraploid hybrid of P. anomala and either P. arietina, P. humilis, P. officinalis, P. parnassica or less likely P. tenuifolia, or one of their (now extinct) common ancestors. P. banatica is the tetraploid hybrid of P. mairei and one of this same group. P. broteri, P. coriacea, P. clusii, P. rhodia, P. daurica subsp. mlokosewitschi, P. mascula subsp. hellenica and ssp. mascula, and P. daurica subsp. wittmanniana are all descendants of hybrids of P. lactiflora and P. obovata.  
According to recent genetic analyses, the monogeneric family Paeoniaceae is related to a group of families with woody species in the order Saxifragales. This results in the following relationship tree.  One dissertation suggests the section Onaepia branches off earliest. A later publication of the same author and others suggests the Moutan-section splits off first. Within that section P. ludlowii and P. delavayi are more related to each other than to any other species
The section Moutan is divided into P. delavayi and P. ludlowii, together making up the subsection Delavayanae, and P. catayana, P. decomposita, P. jishanensis, P. osti, P. qiui and P. rockii which constitute the subsection Vaginatae. Known diploid taxa in the Paeonia-section are P. anomala, P. lactiflora, P. veitchii, P. tenuifolia, P. emodi, P. broteri, P. cambedessedesii, P. clusii, P. rhodia, P. daurica subsps. Tetraploid
taxa are P. arietina, P. officinalis, P. parnassica, P. banatica, P. russi, P. peregrina, P. coriacea, P. mascula subsps. P. russi is the tetraploid hybrid of diploid P. lactiflora and P. mairei, while P. cambedessedesii is the diploid hybrid of P. lactiflora, likely P. mairei, but possibly also P. obovata. P. peregrina is the tetraploid hybrid of P. anomala and either P. arietina, P. humilis, P. officinalis, P. parnassica or less likely P. tenuifolia, or one of their (now extinct) common ancestors.