Paeonia rockii((Hong, De-Yuan. “Peonies of the World. Taxonomy and phytogeography.” Kew: Royal Botanic Gardens, 2010, pp. 78-83.))
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:
1a. Leaflets lanceolate to ovate-lanceolate, all or mostly entire: subsp. rockii
1b. Leaflets ovate to ovate-orbicular, all or mostly lobed: subsp. atava
Paeonia rockii subsp atava
Chromosome number: 2n=10
Growing in deciduous forests at an altitude of 1,100—1,750 m.
According to our present knowledge, subsp. atava is conﬁned to E Gansu, S Ningxia and Shaanxi on northern slopes of the Qinling Range and further N.
The subspecies is clearly differentiated from the typical one in having the leaflets ovate or ovate-orbicular, mostly or all lobed. In this subspecies, the petals are usually white with a large, dark purple blotch at the base, but in the Longbagou Mountain, Xiashiwan Township (Ganquan County, Shaanxi Province), we found a population (D. Y. Hong, K. Y. Pan & Y. Ren H06003) in which white-ﬂowered and red- ﬂowered individuals coexisted.
Readers may feel surprised when we state that P. rockii subsp. atava (Brühl) D. Y. Hong is confined to a small area in eastern Gansu, southern Ningxia and Shaanxi, as the type was from Yadong, Xizang (Tibet). Hong (1997) explained this clearly. Paeonia rockii subsp. atava is native to the Qinling Range and further north. It is highly possible that Buddhist monks from Mt Taibai in the Qinling Range cultivated this peony. Many individuals of this striking peony are cultivated in front of the Dadian Lamasery on Mt Tabai and distributed to lamaseries elsewhere.