Habit and leaf form. Soft shrubs (or subshrubs), or herbs (usually). Sometimes tuberous. Leaves large; alternate; spiral; petiolate; non-sheathing; not gland-dotted; compound; ternate, or multiply compound (mostly ternately or ternate-pinnately twice or more compound or dissected). Lamina primarily palmately veined; cross-venulate. Leaves exstipulate; without a persistent basal meristem.
Leaf anatomy. Stomata present; anomocytic.
The mesophyll containing calcium oxalate crystals. The mesophyll crystals druses. Minor leaf veins without phloem transfer cells (Paeonia).
Stem anatomy. Nodes tri-lacunar, or penta-lacunar. Cortical bundles present. Secondary thickening developing from a conventional cambial ring. Xylem with vessels. Vessel end-walls oblique; scalariform, or scalariform and simple. Wood parenchyma very scarce apotracheal (limited to a few cells among the fibres). Sieve-tube plastids S-type.
Reproductive type, pollination. Plants hermaphrodite. Pollination entomophilous; commonly via diptera.
Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’ (few flowered), or solitary. Inflorescences or solitary flowers terminal. Flowers bracteate; medium-sized to large; regular to somewhat irregular (the sepals sometimes somewhat unequal); acyclic. The perianth acyclic, the androecium acyclic, and the gynoecium acyclic (the phyllotactic spiral continued through bracts, perianth, androecium trunk vascular bundles and (usually) gynoecium). Floral receptacle markedly hollowed to not markedly hollowed. Free hypanthium absent. Hypogynous disk present; intrastaminal; annular (lobed or forming a large, subglobose envelope around the gynoecium), or of separate members (interpreted as either receptacular, or modified androecium).
Perianth with distinct calyx and corolla; (8–)10–15(–20). Calyx (3–)5(–7); polysepalous; persistent (leathery); much imbricate. Corolla 5–8(–13); polypetalous; imbricate; regular (the petals large); white, or red, or purple. Petals sessile (orbicular).
Androecium 50–150 (‘many’). Androecial members branched (associated with five vascular trunks); maturing centrifugally; free of the perianth; free of one another (the vascular trunks not reflected in detectable clusters). Androecium exclusively of fertile stamens, or including staminodes (sometimes, if the intrastaminal glands are interpreted as androecial). Stamens 50–150 (‘many’); polystemonous. Anthers basifixed, or adnate; dehiscing via longitudinal slits; extrorse; tetrasporangiate. Microsporogenesis simultaneous. Anther wall initially with one middle layer, or initially with more than one middle layer; of the ‘dicot’ type. Tapetum glandular. Pollen shed as single grains. Pollen grains aperturate; 3 aperturate; colporate (colporoidate); 2-celled.
Gynoecium (2–)3–5(–15) carpelled; apocarpous; eu-apocarpous (the carpels arcuate-divergent); superior. Carpel non-stylate to stylate; apically stigmatic (the expanded, falcate stigma sessile or on a short, stout style); 10–100 ovuled (‘several to many’). Placentation marginal (the ovules biseriate). Stigmas wet type; papillate; Group III type. Ovules funicled; biseriate; arillate; anatropous; bitegmic (the outer integument thick, ultimately two-layered, resulting in a three-layered testa); crassinucellate (the nucellus degenerating after pollination). Outer integument contributing to the micropyle. Embryo-sac development Polygonum-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3; not proliferating; persistent. Synergids with filiform apparatus. Hypostase present. Endosperm formation nuclear. Endosperm haustoria present; chalazal. Embryogeny very peculiar — involving an unequal first zygotic division with degeneration of the smaller daughter cell, and nuclear divisions in the larger one resulting in a coenocytic, free-nuclear stage with the embryo formed by budding from the coenocyte.
Fruit non-fleshy; an aggregate. The fruiting carpel dehiscent; a follicle. Seeds endospermic. Endosperm oily. Seeds large (with a funicular aril); with amyloid. Embryo well differentiated (but minute). Cotyledons 2. Embryo achlorophyllous (1/4); about 0.2 the length of the seed. Testa red (at first), or black (subsequently, glossy).
Seedling. Germination phanerocotylar, or cryptocotylar.
Physiology, biochemistry. Not cyanogenic. Alkaloids absent (?). Iridoids not detected. Proanthocyanidins absent. Flavonols present; kaempferol and quercetin. Ellagic acid absent. Saponins/sapogenins absent. C3. C3 physiology recorded directly in Paeonia.
Geography, cytology. Holarctic. Temperate. North temperate, excluding Eastern America and Japan. X = 5.
Taxonomy. Subclass Dicotyledonae; Crassinucelli. Dahlgren’s Superorder Malviflorae; Paeoniales. Cronquist’s Subclass Dilleniidae; Dilleniales. APG 3 core angiosperms; core eudicot; unplaced at Superordinal level; Order Saxifragales.
Species 33. Genera 1; only genus, Paeonia.
Family circumscription discussed by Melville (1982).
• Technical details: Paeonia.
• Paeonia brownii: Bot. Reg. 1839, 30.
• Paeonia mascula (as P. corallina): Eng. Bot. 50, 1863.
Then glut thy sorrow on a morning rose,
Or on the rainbow of a salt sand-wave,
Or on the wealth of globèd peonies
(John Keats, ‘Ode on Melancholy’)