Shrubs 0.2—1.8 m tall, glabrous throughout. Roots tuberous with tubers up to 8 cm long, 2 cm in diameter. Stems grey, 1.5 cm in diameter, shoots green, sometimes pink, with 5-9 yellow or pink scales at the base, simple but often with sterile branches in axils, occasionally branches developed and ﬂowering. Petioles 10—22 cm long; lower 2 or 3 leaves biternate or ternate—pinnate, ovate in outline, 15—30 cm long (excl. petioles), 10—22 cm wide; leaﬂets 9, more—or—less decurrent, ﬁrst divided into 3—11 primary segments; segments divided again mostly to near the base or halfway into 2—11 secondary segments, thus each lower leaf with (17-)40-100(-312) segments; petiolules of middle primary divisions 5-9 cm long, petiolules of lateral primary divisions 1-3 cm long, petiolules of secondary divisions much shorter; segments linear, linear-lanceolate, entire or occasionally lobed, 1.5—10 cm long, 0.5—4.5 cm wide; lobes similar to segments but shorter; segments and lobes acute at the apex. Flowers usually 2—3 on a shoot, terminal and axillary, forming a cyme, less frequently solitary and terminal, occasionally 4, more-or-less pendulous, the terminal one blooming ﬁrst, the third one from the top second, the fourth from the top the third, whereas the second from the top blooms last; involucrate bracts 1—5, leaf-like, the outer ones 2—4—segmented, green; sepals 2—9 in number, green outside, green but pink at the base inside, or entirely purple or purple-red, rounded or triangular-rounded, mostly caudate, rarely rounded at the apex. 1.3—3.7 cm long, 0.6—2.3 cm wide; petals 4—13, but mostly 7-11 in number, yellow, yellow with a red or purple—red spot at the base, red, dark red, or dark purple—red, sometimes white, orange, green-yellow, or yellow with red margins; stamens 25—160; ﬁlaments yellow, pink, red, or dark purple-red; anthers yellow, pink, red, or dark purple-red; disk ﬂeshy, short, annular or short-cylindrical, 1—3 mm high, incised, green, yellowish, yellow, red or dark red; carpels 2-4, very rarely 6-8; ovaries usually green, sometimes purple; stigmas sessile, yellow-green, yellow, red or purple-red; ovules 7—17 per carpel. Follicles oblong—ovoid, 2—4 cm long, 1-1.5 cm wide, brown at maturity. Seeds 1—6 in each follicle, brown-black, oblong, c. 10 mm long, c. 8 mm in diameter.
Chromosome number: 2n = 10 (diploid).
Paeonia delavayi was collected at altitudes from 1,900 to 4,000 m, primarily in sparse thickets or dry Pinus and Quercus woods, rarely on grassy slopes or glades of virgin Picea forests. The taxon is endemic to China and restricted to western Sichuan, eastern Xizang (Tibet) and Yunnan.
Plants of Paeonia delavayi are always dwarf shrubs. The tallest plants (ca. 1.8 m) were found in Yunshanping, Lijiang, northwestern Yunnan (D. Y. Hong et al. H97103), where they grew in Picea likiangensis (Franch.) E. Prit. forest at altitudes of c. 3,200 m. By contrast, the shortest plants (rarely reaching 1 m) were found in Ganghaizi, Lijiang (D. Y. Hong et al. H97095), about 20 km SE of the Yunshanping population, growing in dry, sparse Pinus densata—Quercus spinosa forest. Many dwarf individuals had woody parts underground, and only annual shoots emerged above ground. Plants of the other populations that we studied were intermediate between these two.
Although the leaves of Paeonia delavayi are biternate or ternate—pinnate, the leaf segments are quite variable in number, length and width. The number of segments ranged widely from 17 to 312 (Hong et al. 1998), and seemed to differ between populations. For example, segment number varied from 17 to 49 in the population D. Y. Hong et al. H96024 (A, K, MO, PE, US), and from 68 to 312 in the population D. Y. Hong et al. H95063 (A, K, MO, PE, US). However, the standard deviation of the variation in number of leaf segments (Hong et al. 1998) shows that these two populations are just the extremes of a wide range of variation that was also observed within given populations. Taking all the populations into consideration, the number of segments varied continuously in this species. Paeonia potaninii was described as new by Komarov in 1921 because it was considered to have narrower leaf segments than P. delavayi. However, the width of leaf segments also varies greatly, ranging from 0.4 to 2.8 cm within P. delavayi, and from 0.76 to 1.83 cm in the population D. Y. Hong et al. H95070 (PE) from the type locality of P. potaninii. The D. Y. Hong et al. H95070 population falls in the middle of the overall variation ranges for leaf-segment width (Hong et al. 1998) and length in this species. Therefore, it is evident that P. potaninii is similar to P. delavayi in this respect.
Stern (1946) distinguished Paeonia delavayi from its allies by the presence of a conspicuous involucre immediately below the calyx. Across the genus, however, it is difficult to distinguish clearly between involucrate bracts and sepals, and there is also a gradation between leaves and involucrate bracts. We designate the laminae borne some distance below the ﬂowers as leaves, and those at the top of shoots and immediately below the calyx as involucrate bracts. lnvolucrate bracts, so designated, have various forms, ranging from segmented and leaf-like to entire and sepal-like. The sepals have a much broader proximal part and a dark green, smaller and narrower distal part that has a mucronate or rounded apex. The total number of bracts and sepals varies greatly both within and between populations of P. delavayi. The population D. Y. Hong et al. H97103 (A, K, MO, PE, US), with dark red ﬂowers, at Yunshanping, Lijiang, which corresponds to the type locality of P. delavayi (Stern 1946), indeed had the highest number of bracts and sepals (10 or 11) forming the so-called conspicuous involucre, whereas other populations observed by us had fewer bracts and sepals. However, the difference was not signiﬁcant (Hong et al. 1998). Another population D. Y. Hong et al. H97095 (A, K, MO, PE, US), only about 20 km from H97103, was variable in number of both bracts and sepals, and some ﬂowers had 10 or 11 bracts and sepals (Hong et al. 1998), similar to those in the H97103 population. The same total number of bracts and sepals were found in these populations and in D. Y. Hong et al. H97087 (A, K, MO, PE, US), which had pure yellow or yellow petals with a dark red blotch at the base. Plate 1 in Hong et al (1998) and the remarks above demonstrate clearly that there is a continuous variation in the number of bracts and sepals, and that no correlation exists between petal colour and the total number of bracts and sepals. Therefore, P. delavayi cannot be separated from P. potaninii, P. lutea, P. trollioides and similar names.
Variation in the number and colour of ﬂoral parts extends to the sepals, which vary in colour both on a single ﬂower and within populations (Hong et al., 1998). They are usually green, but sometimes dark red or purple (Hong et al., 1998). In addition, the sepals vary greatly in size both within and between populations, and the variation was seen as continuous (Hong et al., 1998). Although population H97103 from Yunnan had larger sepals than other populations, the formation of a conspicuous involucre is not unique in this species as alleged by Stern (1946).
Petal colour has been much emphasised in the taxonomy of the Paeonia delavayi complex, used by various authors (Finet & Gagnepain, 1904; Stern, 1946; Fang, 1958) in distinguishing the yellow corollas in P. lutea from the dark red ones seen in P. delavayi. As shown by Hong and his co-workers (Hong et al. 1998), petal colour is extremely variable between and within populations (Hong et al. 1998). In the populations D. Y. Hong et al. H97112 and H97128 from Xianggelila, Yunnan, various petal colours appeared, and a few individuals in the latter population even had white petals. On the basis of the literature and our own observations, red, dark red or dark purple-red petals occur in the northeastern portion of the distributional range, while yellow petals or yellow petals with a dark red spot at the base were found in the northeast, west, and south. Therefore, petal colour is very variable within a given region or population, showing only a weak geographical differentiation, and is not correlated with other characters. Furthermore, petal colour was extremely variable in populations such as H97112 and H97128, both from northwestern Yunnan.
Unlike the ﬂoral disk of the other species of sect. Moutan, the disk in Paeonia delavayi and P. ludlowii is generally short and ﬂeshy. In the populations H97112 and H97119, the disk secreted abundant nectar in some ﬂowers, and it seems likely that this secretion made these ﬂowers more scented. The disk, including the incised teeth, varied in height from 1 to 3 mm, and in colour from pale yellow or yellow to red, even within a single population (e.g. H97112). Therefore, these disk characters are also of little, if any, taxonomic importance in this group.
Paeonia delavayi has the widest geographical range in section Moutan. The plants predominantly reproduce vegetatively, and cloning by stolons (Hong et al., 1998) was commonly seen in every population visited except for the population D. Y. Hong et al. H97103 (A, K, MO, PE, US) in Picea likiangensis forest in Yunshanping, Lijiang, Yunnan. Vegetative reproduction probably predominates in P. delavayi, and seedlings were very rarely found in the ﬁeld. It was even more predominant at the northwestern and northern boundaries of the distributional range. In Yajiang County, in western Sichuan, the population H95070 was found near a village, where some individuals were growing by fences and on newly stabilised debris. In this population, only about 50% of the follicles were developed and, because of insect damage, only 20% had seeds. Cloning by stolons, however, was common. Additionally, examination in the spring of 1996 of all follicles from the ﬁve populations in Xizang (Tibet) produced in 1995 found no seeds. No follicles were observed in a population (from temple ruins in the village of Xituan, Gengzhanglungba Valley, Nyingchi County, Xizang (Tibet)) that consisted of numerous individuals over an area of about 250 m2. This population probably developed from individuals produced by cloning. Clonal growth by stolons was found in every population visited (Hong et al., 1998). The roots of P. delavayi are always fusiformly thickened (Hong et al., 1998). Such roots and stolons probably make the species more adapted to open, somewhat dry and disturbed habitats, and enable the species to establish rapidly forming a new population. It may also account for the scattered distribution of the species and the large number of individuals in any given population. Paeonia delavayi (var. lutea) has been listed as an endangered species in the China Plant Red Data Book (Feng in Fu & Jin, 1992). On the basis of its vegetative reproduction and relatively wide distribution, however, it is reasonable to conclude that this species will not become extinct so long as wanton digging is controlled (Hong et al., 1998, 2003).
- Hong, De-Yuan. “Peonies of the World. Taxonomy and phytogeography.” Kew: Royal Botanic Gardens, 2010, pp. 66-71.