How to identify your peony species?
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| 1A. Shrubs; disk leathery and halfway to wholly enveloping carpels until mid-anthesis, or fleshy and short, enveloping only the base of carpels: sect. Moutan | |
| 1B. Herbaceous perennials; disk fleshy and short, enveloping only base of carpels | |
| 2A. Petals nearly equal in size to or smaller than sepals; disk dentate, almost interrupted; lower leaves ternate or biternate, with leaflets 3 or 9, lateral roots slightly fusiform: sect. Onaepia | |
| 2B. Petals much larger than sepals; disk annular, waved or flat; lower leaves biternate or triternate, with leaflets 9 or more; lateral roots carrot-shaped, fusiform or tuberous: sect. Paeonia | |
| 2A. Flowers usually 2-4 in a cyme, more or less pendent; disk fleshy, enveloping only the base of the carpels; carpels always glabrous: subsect. Delavayanae |
| 2B. Flowers solitary, erect; disk leathery, enveloping carpels halfway or completely until mid- anthesis; carpels tomentose or glabrous: subsect. Vaginatae |
| 3A. Carpels glabrous, 2-5; disk enveloping carpels halfway or up to the base of the styles until mid-anthesis; lower leaves decompound with leaflets (29-)33-63 in number, all lobed | |||
| 4A. Carpels almost always 5, rarely 4 or 3; disk enveloping carpels halfway at anthesis; leaflets 35-63 in number, elliptic to narrowly rhomboid: P. decomposita | |||
| 4B. Carpels mostly 3, less often 4 or 2, rarely 5; disk enveloping carpels up to base of styles at anthesis; leaflets (19-)25-35(-39) in number, rhomboid to nearly orbicular: P. rotundiloba | |||
| 3B. Carpels densely lanate or tomentose, 5(-7); disk completely enveloping carpels until mid-anthesis; lower leaves biternate, biternate-pinnate or ternate-bipinnate; leaflets usually fewer than 20(-33) in number, if more at least some of them entire | |||
| 4A. Lower leaves biternate; leaflets 9 in number, very occasionally 11 or 15 in P. jishanensis | |||
| 5A. Leaflets ovate or ovate-orbicular, mostly entire, often reddish above; petals often with a reddish blotch at the base: P. qiui | |||
| 5B. Leaflets oval, ovate or nearly orbicular, mostly or all lobed; green above; petals without a blotch at the base | |||
| 6A. Leaflets oval or ovate, terminal leaflets 3- or 5-cleft, with additional 1 to several lobes, lateral leaflets mostly 2- or 3-lobed, less frequently entire; lobes acute at apex; leaves glabrous on lower surface; sepals all caudate or mucronate: P. cathayana | |||
| 6B. Leaflets ovate-orbicular to orbicular, all 3-cleft; segments lobed, acute to rounded at apex; leaves villose along veins on lower surface; sepals all rounded at apex: P. jishanensis | |||
| 4B. Lower leaves ternate-pinnate, ternate-bipinnate or biternate-pinnate; leaflets more than 9 in number, usually oval to lanceolate, mostly entire, less frequently oval-orbicular and mostly lobed | |||
| 5A. Lower leaves ternate-pinnate; leaflets no more than 15 in number, ovate to ovate-lanceolate, mostly entire; petals white, rarely pale pink, without a blotch: P. ostii | |||
| 5B. Lower leaves ternate-bipinnate (rarely biternate-pinnate); leaflets (17-)19-33 in number, lanceolate or ovate-lanceolate and mostly entire, or ovate to ovate-orbicular and mostly lobed; petals white, rarely red, always with a large, dark purple blotch at the base: P. rockii | |||
3A. Lower leaves biternate; leaf segments and final lobes 55-110 in number, acute to rounded at apex; carpels usually 5, rarely 3, 4 or 6 in number; sepals exceeding petals: P. brownii
3B. Lower leaves ternate; leaf segments and final lobes 30-78 in number, mostly acute at apex; carpels usually 3, rarely 2 or 4; sepals slightly smaller than, or subequal to, petals: P. californica
| 3A. Flowers several to a stem, less frequently solitary but with 1-2 undeveloped flower buds at axils, rarely really solitary; sepals mostly caudate at apex; leaves usually with bristles along veins above: subsect. Albiflorae | |
| 3B. Flowers always solitary and terminal; sepals mostly rounded at apex; leaves glabrous or with bristles along veins above. | |
| 4A. Lateral roots always tuberous; leaflets or leaf segments of lower leaves mostly more than 20 in number, rarely fewer; leaves covered with bristles along veins above, or, if glabrous above, nearly always villose beneath: subsect. Paeonia | |
| 4B. All roots carrot-shaped; leaflets or leaf segments of lower leaves numbering up to 21 (only in P. broteri up to 32 and in P. clusii 23—95); leaves always glabrous above: subsect. Foliolatae | |
| 5A. Leaves cartilaginous and denticulate on margin, pubescent along veins or glabrous beneath; carpels glabrous, very rarely hairy: P. lactiflora | ||
| 5B. Leaves smooth on margin, glabrous beneath; carpels glabrous or hairy | ||
| 6A. Leaflets or leaf segments of lower leaves 70-100 in number: P. anomala | ||
| 6B. Leaflets or leaf segments of lower leaves fewer than 30 in number | ||
| 7A. Carpels 1, rarely 2 in number, mostly tomentose, less frequently glabrous; flowers often several per stem: P. emodi | ||
| 7B. Carpels mostly 2 or 3 in number, rarely 4, always glabrous; flowers nearly always solitary, rarely 2 in number, but sometimes with 1-2 undeveloped flower buds at axils: P. sterniana | ||
| 5A. Stems mostly hirsute; sepals mostly hairy on abaxial side; leaves always glabrous or rarely villose at base above, more or less villose beneath | |||
| 6A. Leaflets or leaf segments of lower leaves mostly more than 20, very rarely as few as 11 in number, linear-elliptic or lanceolate; sepals hispidulous or glabrous on abaxial side: P. officinalis | |||
| 6B. Leaflets or leaf segments of lower leaves mostly less than 20, occasionally up to 32 in number; elliptic, oblong or ovate-lanceolate; sepals densely villose on abaxial side | |||
| 7A. Flowers rose to red; anthers yellow; leaflets or leaf segments of lower leaves 11-25, occasionally up to 32 in number: P. arietina | |||
| 7B. Flowers dark purple; anthers orange; leaflets or leaf segments of lower leaves 9-15, occasionally up to 25 in number: P. parnassica | |||
| 5B. Stems glabrous; sepals always glabrous; leaves mostly with bristles along veins above | |||
| 6A. Leaflets or leaf segments always dentate-lobed, with lobes less than 1 cm long; stigmas yellow or pale pink: P. peregrina | |||
| 6B. Leaflets or leaf segments entire or rarely deeply lobed; stigmas red | |||
| 7A. Leaflets or leaf segments of lower leaves 19-45 in number; leaves hispidulous beneath: P. saueri | |||
| 7B. Leaflets or leaf segments of lower leaves more than 70 in number; leaves always glabrous beneath | |||
| 8A. Leaflets or leaf segments of lower leaves 130-340 in number, mostly filiform, 0.5—8 mm wide: P. tenuifolia | |||
| 8B. Leaflets or leaf segments of lower leaves 70-100 in number, linear, 4-18 mm wide: P. intermedia | |||
| 5A. Leaflets or leaf segments of lower leaves 23-95 in number, linear to ovate: P. clusii | |||||||
| 5B. Leaflets or leaf segments of lower leaves numbering less than 21 (up to 32 in P. broteri), broad elliptic to obovate | |||||||
| 6A. Leaflets or leaf segments acuminate to caudate-acuminate at apex; carpels densely brown-papillose or hispidulous, rarely glabrous: P. mairei | |||||||
| 6B. Leaflets or leaf segments acute to mucronate at apex; carpels tomentose or glabrous | |||||||
| 7A. Lower leaves with 9 or fewer leaflets; carpels always glabrous | |||||||
| 8A. Carpels 3-10, mostly 4-6 in number; plants purple-red and glabrous throughout: P. cambessedesii | |||||||
| 8B. Carpels mostly 2 or 3, rarely 1, 4 or 5 in number; plants usually green; leaves more or less hirsute beneath: P. obovata | |||||||
| 7B. Lower leaves usually with 10-15 leaflets or segments, less frequently 9 or more; carpels mostly tomentose | |||||||
| 8A. Carpels 1, less frequently 2 in number, nearly always glabrous, very occasionally sparsely hairy; follicles columnar, 4-5.4 cm long: P. algeriensis | |||||||
| 8B. Carpels (1-)2-4 in number, rarely more, mostly tomentose; follicles long-ovoid or ellipsoid, up to 4 cm long | |||||||
| 9A. Styles 1.5-3.5 mm long; leaflets or leaf segments of lower leaves 11-14, rarely up to 17 in number, densely or sparsely villose beneath; carpels always glabrous: P. kesrouanensis | |||||||
| 9B. Styles usually absent (only in P. corsica 1.5-3 mm long); leaflets/leaf segments of lower leaves 9-20 in number, glabrous, sparsely hispid, puberulent or villose beneath; carpels tomentose or glabrous | |||||||
| 10A. Carpels always lanate or tomentose with hairs 2-3 mm long; styles absent | |||||||
| 11A. Leaflets usually entire, leaflets or leaf segments of lower leaves 9, rarely 10, very occasionally 11 in number, usually ovate, rounded, nearly truncate with a mucro, or rounded, less frequently acute at apex: P. daurica | |||||||
| 11B. Leaflets at least some segmented, leaflets or leaf segments of lower leaves usually numbering 10 or more, very occasionally 9, usually acute at apex | |||||||
| 12A. Leaflets or leaf segments of lower leaves mostly (11-)15-21, rarely up to 32 in number, 4-10(-15) cm long, 1.5-5(-6.5) cm wide; leaves always glabrous; hairs on carpels 2 mm long: P. broteri | |||||||
| 12B. Leaflets or leaf segments of lower leaves mostly (9-)11-15, rarely up to 21 in number, 9-18 cm long, 4.5-9 cm wide; leaves sparsely hispid or glabrous; hairs on carpels 3 mm long: P. mascula | |||||||
| 10B. Carpels glabrous or tomentose with hairs 1.5 mm long; styles present or absent | |||||||
| 11A. Carpels tomentose, rarely glabrous; leaflets or leaf segments of lower leaves usually 9, rarely up to 20 in number, holosericeous beneath; styles 1.5-3 mm long: P. corsica | |||||||
| 11B. Carpels glabrous, very occasionally sparsely hairy; leaflets or leaf segments of lower leaves 10-15 in number, glabrous, very occasionally sparsely hairy (hairy leaves always accompanied by hairy carpels); styles lacking: P. coriacea | |||||||
Source: “Key to species.” In: Hong De-Yuan. “Peonies of the World. Polymorphism and diversity.” Royal Botanic Gardens: Kew, 2011, pp. XII-XV.
Some paeonia species:
A/ P. jishanensis B/ P. decomposita C/ P. rockii D/ P. ostii
E/ P. qiui F/ P. delavayi G/ P. ludlowii H/ P. lactiflora
I./ P. mairei J/ P. sterniana K/ P. anomala L/ P. obovata
