Paeonia ludlowii

Paeonia ludlowii
↑flower, ↓habit, showing grey/brown old stems topped by new shoots
Scientific classification
Kingdom:	Plantae
(unranked):	Angiosperms
(unranked):	Eudicots
(unranked):	Core eudicots
Order:	Saxifragales
Family:	Paeoniaceae
Genus:	Paeonia
Species:	P. ludlowii
Binomial name
Paeonia ludlowii (Stern & G.Taylor) D.Y.Hong
Synonyms
P. lutea var. ludlowii P. delavayi ssp. ludlowii [1]

Paeonia ludlowii, is a medium high, deciduous shrub, belonging to the peonies, that is endemic to South-East Tibet. In Tibet it is known as lumaidao meaning "God’s flower". The vernacular name in China is 大花黄牡丹 (da hua huang mu dan) meaning "big yellow-flowered peony". In English it is sometimes called Tibetan tree peony or Ludlow's tree peony. It has pure yellow, slightly nodding, bowl-shaped flowers, and large, twice compounded, light green leaves.^[2][3][4]

Description

young shoot with two flowerbuds

P. ludlowii is a hairless, deciduous shrub of 2-3½ m high. It has ten chromosomes (2n=10).

Stems and leaves

The roots get narrower further down and are not fused together. There are no creeping stems (or stolons). The grey to light brown stems grow in clumps (or caespitose), do not branch often, remain approximately the same width during the growing season, and after some years may reach 4 cm in diameter. Young stems are light green, with at their base eight to twelve scales. Leaves are light green above and glaucous pale green below. In the lowest leaves, the leaf stalk is 9–15 cm long, while the leaf blade is twice compounded or deeply divided (or biternate), with the primary leaflets on a short stem of 2–3 cm, the leaflet blades 6-12 × 5–13 cm, those usually incised almost to the base, having three segments, at base extending along the stalk until disappearing (or decurrent). Each of the segments 4-9 × 1½-4 cm, mostly incised to midlength into three lobes of 2-5 × ½-1½ cm, with an entire margin or one or two teeth, pointy at their tips.^[3][4]

Inflorescence

The slightly nodding bisexual flowers grow with three to four on each shoot, extending from the axil of the leaves, they are 10–12 cm wide and sit on a flower stalk of 5–9 cm long, and open late May and early June. Each flower is subtended by four or five lance-shaped bracts. There are three to five green sepals with a rounded outline of 1½-2½ cm, which have a rounded tip that suddenly narrows into a point. The pure yellow, inverted egg-shaped petals are spreading but slightly curved inwards, 5-5½ × 2½-3½ cm and have a rounded tip. The numerous filaments are yellow, 1-1½ cm long, topped by yellow anthers of about 4 mm long. The yellow disk at the base of the carpels is ring-shaped, carries teeth, and about 1 mm high. At the centre of each flower are one or two carpels that are topped by yellow stigmas.^[3][4]

Fruit and seed

The carpels develop into cylindrical fruits (or follicles) of 4¾-7 × 2-3⅓ cm. These contain eventually dark brown, globose seeds of 1⅓ cm in August.^[3][4]

Differences with related species

Paeonia delavayi is closely related to P. ludlowii, but can easily be distinguished because it reproduces mainly by stolons, has fused roots, stems emerge from the ground individually, is only up to 1¾ m high, has segmented leaves with narrow and acute segments. Petals, stamens, disk, and stigmas may be yellow, maroon, orange or white. It has two to eight carpels, which develop in small follicles (2-3½ × 1-1½ cm) and rarely produce seeds. P. ludlowii on the other hand can only reproduce by seed and lacks creeping underground stems, has slender, regular roots, while the stems form a clump, grows to 2-3½ m high, has leaves with short and suddenly pointed lobes, petals, stamens, disk and stigmas are always yellow, only one or very rarely two carpels develop but this grows into a much larger follicle (4¾-7 × 2-3⅓ cm) which always develops seeds.^[5]

Other species of tree peony do not have yellow flowers, do not grow as large and generally have darker green foliage and darker brown bark. Some of the many cultivated cross-breeds of tree peonies may have yellow flowers, but these are not nodding, generally much larger, mostly double flowered, with darker green leaves and much lower.^[6]

Taxonomy

seeds

In 1886 P. delavayi with maroon-red and P. lutea with yellow flowers, both from Northwest Yunnan, were described respectively by Franchet and Delavay, on the same page of the same scientific article. In 1904 Finet and Gagnepain thought these should both be regarded varieties of P. delavayi. In 1953 F.C. Stern and George Taylor described one more taxon, P. lutea var. ludlowii, discovered in southeastern Tibet. In their description of Paeonia lutea var. ludlowii, these authors indicate that it is distinctly different from variety lutea. Recent analysis shows that these differences between ludlowii and the other described taxa in the P. delavayi-group are consistent whilst the character states within the other taxa occur in any combination. Therefore Hong concludes that ludlowii should be acknowledged as a distinct species, while the other taxa cannot be upheld and should be synonymized with P. delavayi.^[4][5]

Phylogeny

Paeonia is the only genus recognized in the Paeoniaceae family. Three sections are distinguished: an early branching Onaepia that consists of both native North-American species P. brownii and P. californica, section Paeonia, which comprises all Eurasian herbaceous species, and the section Moutan, which includes all woody species from China, including Tibet. These relations are represented by the following tree.^[5]

Etymology

The species was named in his honor Frank Ludlow who collected seed of Paeonia ludlowii in the Tsangpo Valley (upper Bhramaputra river) in 1936 for the first time known to western science, on his expedition with Major George Sherriff in South-East Tibet.^[2]

Distribution and ecology

Paeonia ludlowii is an endemic that is restricted to the Nyingchi, Mainling and Lhünzê counties of South-East Tibet. It grows in open forests, and thickets on dry rocky slopes at elevations of 3000-3500m.^[2][3][4] Individual populations are small in area but have a large number of individuals. Because the seeds are quite large, almost all seeds germinate close to the parent, and are often found in a large density. Perhaps rats are the most effective mains of seed dispersal to somewhat distanced new locations.^[4]

Cultivation

Paeonia ludlowii is sometimes grown as an ornamental, mostly for its delicate foliage. In cultivation, it does best in fertile, neutral to slightly alkaline, well-drained soil. Specimens prefer to be planted deep and dislike to much water. In early spring and during summer high-potash liquid feed stimulates richer flowering.^[2] When growing the species from seed, these can best first be soaked, mixed with damp vermiculite, and kept at room temperature until root emerges after one to three months. If kept cool afterwards, the shoot appears after a further two to three months. When these are planted into separate pots immediately and grown in daylight results are generally good.^[7]

The shoot only appears at a root length of at least 6 cm has developed. The epicotyl remains dormant until the GA3/ABA ratio is sufficiently different.^[8]

Tree peonies in general can suffer from peony wilt (Botrytis paeoniae, a grey mould blight) and verticillium wilt, which may cause wilting and dieback of young shoots. In infected soils, honey fungus can cause instant death.^[9]

Use

The species is used as a traditional medicin, and local people dig it up for its root bark. Exploitation by people from other parts of China is a serious threat to the survival of this species.^[4] It is sometimes used as an ornamental for its ferny foliage in botanical gardens and by plant collectors.

References

Media related to Paeonia ludlowii at Wikimedia Commons