Paeonia rockii((Hong, De-Yuan. “Peonies of the World. Taxonomy and phytogeography.” Kew: Royal Botanic Gardens, 2010, pp. 78-79.))
Shrubs to 1.8 m tall. Roots cylindrical, attenuate downwards. Turions absent. Stems grey or grey—brown, peeling off in ﬂakes. Lower leaves ternate—pinnate, ternate—bipinnate or biternate—pinnate, with 17-33 leaﬂets; leaflts lanceolate to ovate—lanceolate and mostly entire, or ovate to ovate-orbicular and mostly lobed, 2—11 cm long, 1.5-4.5 cm wide, glabrous above, villose along veins beneath, truncate to cuneate at the base, acute or acuminate at the apex. Flowers solitary, terminal; involucrate bracts 3—4 in number, leaf—like; sepals 4—7 in number, green, ovate-lanceolate, ovate-orbicular or orbicular, all caudate at the apex, 3—4 cm long, 3—4.5 cm wide; petals 8—13 in number, obovate, entire or irregularly incised, white or rarely red, with a large and dark purple blotch at the base, 5-9 cm long, 4—7 cm wide; filaments yellow; anthers yellow; disk entirely enveloping carpels at anthesis, pale yellow, leathery, dentate or lobed at the apex; carpels 5, rarely 6, densely tomentose; styles 0.5-2 mm long, tomentose; stigmas pale yellow. Follicles oblong, densely yellow tomentose, c. 3 cm long.
Chromosome number: 2n=10 (diploid)
In deciduous broad-leaved forests, forest margins or thickets, on shady slopes of limestone areas, at altitudes from 850 to 2,800 m.
Conﬁned to S Gansu, W Henan, W Hubei, S Ningxia, Shaanxi, and N Sichuan.
This species is characterised by having lower leaves ternate-pinnate, biternate-pinnate or ternate—bipinnate; leaflets usually number 19-33, very rarely fewer than 19, the ﬁlaments are yellow, with the disk yellowish white and the stigmas yellow, as well as the highly distinctive petals of white, rarely red, with a large dark purple blotch at the base. Thus, this species is clearly distinguished from the remaining four in the Paeonia suffruticosa complex: P. jishanensis, P. ostii, P. qiui and P. cathayana. Its petals are the largest in the whole genus, reaching to 9 x 7 cm in length and width, respectively.
Two allopatric subspecies can be readily recognised by the key couplet below:
Paeonia rockii subsp rockii
Chromosome number: 2n = 10 (diploid)
Usually growing in deciduous forests, usually in limestone areas at an altitude of 850—2,800 m.
Relatively widely distributed in five provinces: SE Gansu, W Henan, W Hubei, S Shaanxi and N Sichuan.