Perennials up to 1 m tall. Roots thick, carrot—shaped. Caudex (rhizomes) c. 2 cm in diameter, up to 15 cm long. Stems single, simple, glabrous. Lower leaves biternate, with some leaflets segmented; leaflets/leaf segments 13-24, but mostly 14—17 in number, oblong-ovate or oblong-lanceolate, 6—16.5 cm long, 1.8—7 cm wide, glabrous, cuneate at the base, usually acuminate or even caudate at the apex. Flowers solitary, terminal; involucrate bracts 1—3 in number, leaf—like or linear; sepals 3—5 in number, green, broadly ovate, all rounded or sometimes one caudate at the apex, 1-1.5 cm long, 0.9-1.2 cm wide; petals 7—9 in number, pink to red, obovate, 3.5-7 cm long, 2—4.5 cm wide, usually rounded at the apex; ﬁlaments purple-red; anthers yellow; disk yellow, annular, c. 1 mm high; carpels 2—3, rarely 1 in number, sparsely to densely yellow papillate to hispidulous, sometimes glabrous; styles up to 4 mm long; stigmas red, 1.2-1.5 mm wide. Follicles 3-3.5 cm long, 1—1.2 cm in diameter. Seeds black, oblong-spherical, 7-8 mm long, 4—5 mm in diameter.
Chromosome number: 2n=20 (Hong et al., 1988; Dr Q. E. Yang, personal communication, locality: Qiaojia County of Yunnan, the type locality). Leeper’s (1968) reports of 2n = 10 for this species seem doubtful. They failed in neither providing the vouchers nor indicating the origin of the materials they used. Our observations on the chromosomes of this species (Hong et al., 1988) and Yang’s work cover four localities in three provinces: Shaanxi in the N of the distribution range, Yunnan in the S, and Sichuan. All show 2n = 20.
Growing in deciduous broad-leaved forests at an altitude of 1,200—3,400 m, on limestones. In Chongqing, SE Gansu, W Hubei, S Shaanxi, C & S Sichuan, and NE Yunnan; endemic to China
Paeonia mairei is a very distinct species with no close relatives evident. It is characterised by caudate-acuminate or acuminate leaflets/leaf segments, conspicuous styles, single stems, and plants that are always entirely glabrous except for the carpels. The presence of indumentum on the carpels is unique in the whole genus.
- Hong, De-Yuan. “Peonies of the World. Taxonomy and phytogeography.” Kew: Royal Botanic Gardens, 2010, pp. 191-193.