Deciduous and caespitose shrubs, up to 3.5 m tall, glabrous throughout. Roots attenuate downward, not fusiform. Stems grey, up to 4 cm in diameter. Shoots green, with 8-12 scales at the base. Lower leaves biternate, green above, pale glaucous beneath; petioles 8-18 cm long; leaﬂets 9, lateral 3 leaﬂets on each side with main petiolules 2-3.5 cm long, terminal 3 leaﬂets with main petiolules 5-11 cm long; leaﬂets nearly sessile, but not decurrent, 6—19 cm long, 5—15 cm wide, 3—segmented to halfway or nearly to the base; segments 4—12 cm long, 1.5—5.5 cm wide, mostly 3—lobed to the middle; lobes 2—5 cm long, 0.5—2.5 cm wide, entire or with 1 or 2 teeth, segments, lobes, and teeth all acuminate at the apex. Flowers 3 or 4 on each shoot, both terminal and axillary, with the terminal one blooming ﬁrst, forming a cyme; pedicels slightly curved, 5-14 cm long, naked or with a leafy bract; involucrate bracts 4 or 5, green; sepals 3 or 4, grading into one another, all or all except one caudate at the apex; petals pure yellow, spreading, obovate rounded at the apex, 4—5.5 cm long, 2.5-3.5 cm wide; ﬁlaments yellow, 1.1—1.5 cm long, anthers yellow, c. 4 mm long; disk ﬂeshy, 1 mm high, yellow, waved; carpels mostly single, very rarely 2; stigmas sessile, yellow. Follicles cylindrical, 4.7—7 cm long, 2—3.3 cm in diameter. Seeds kidney-shaped, dark brown, c. 1.5 cm long, 1.2 cm in diameter.
Chromosome number: 2n=10 (diploid).
Paeonia ludlowii was collected from sparse forests and thickets, on granites at altitudes of 2,870—3,450 m. This is a narrow endemic in southeastern Xizang (Tibet) and known from Nyingchi, Mailing, and Lhünzê counties at 28.4—29.9°N, 92.4—94.8°E.
This species is also a medicinal plant and is often dug out by local people for its root bark. In three of the five populations studied (D. Y. Hong et al. H96007, H96014, H96030), hundreds of individuals were dug out by people from Gansu and Qinghai provinces (Hong, 1997). This has caused a serious threat to the survival of this species. Effective measures must be taken to conserve this beautiful ﬂower.
In the description of Paeonia lutea var. ludlowii, Stern and Taylor (1951, 1953) indicated that the taxon was distinctly different from the variety lutea, distinguished by its long, commonly unbranched stems to 8 feet (2.4 m) vs. 5 feet (1.5 m) in var. lutea, its larger and more open ﬂowers, with up to 2 carpels that are twice as large as those of var. lutea. These differences have been conﬁrmed upon examination of plants in ﬁve populations in Mailing and Nyingchi counties and ﬁve populations of var. lutea (= P. delavayi). As shown in Hong (1997), plants of P. ludlowii are tall from a caespitose base, and have relatively large, pure yellow ﬂowers, yellow ﬁlaments, acuminate leaf segments and lobes, and typically one carpel per ﬂower (more than 97% of the ﬂowers examined had a single carpel and fewer than 3% had two). Furthermore, P. ludlowii produces very large follicles that contain the largest seeds in the genus. By contrast, plants of P. delavayi are not caespitose and have much shorter stems, acute leaf lobes and segments, smaller ﬂowers, yellow petals that are nearly always red-blotched at the base, purple-red ﬁlaments, and three or four, rarely two, much smaller carpels. These differences clearly support the recognition of the variety ludlowii as a distinct taxon and species.
Paeonia ludlowii is a tall shrub that often forms large and dense clumps with dozens of stems. A single individual can have up to 105 ﬂowers (Hong, 1997). All of the five populations studied were small in area, and the largest population was about 200 m in diameter. Except for the Quenima Village population (D. Y. Hang et al. H96020), which had only four individuals, all the populations observed consisted of many rather densely packed individuals, and the species was a dominant element in the community. Two factors may explain the small population areas that contain a large number of individuals. First, this species has a high seed-set, and its seeds appear to have a high germination rate. Nearly 100 seedlings were found in an area of a square meter under a large individual in the Nanyigou population (D. Y. Hang et al. H196030). Second, the seeds of P. ludlowii are large (ca. 1.2 cm diameter) and are not adapted to long-distance dispersal; perhaps they are mostly moved by rats. The species is obligately sexual, and no vegetatively produced individuals or plantlets have been found in any of the populations. More than 20 small plantlets were dug out, and all were found to be seedlings, a sharp contrast to P. delavayi, which reproduces both sexually and vegetatively.
- Hong, De-Yuan. “Peonies of the World. Taxonomy and phytogeography.” Kew: Royal Botanic Gardens, 2010, pp. 61-64.