Paeonia delavayi Franch.

This familiar suckering shrub shows great diversity in height and flower colour, but the attractive, finely divided leaves are a constant, and probably the best reason to grow it. It forms a natural group (subsection Delavayanae) with P. ludlowii, also from western China, but is unlikely to be confused with other woody peonies of subsection Vaginatae. The flowers, while individually attractive, are smaller than those of P. ludlowii and sometimes partly hidden by the leaves. It has proved an adaptable garden plant in Britain, thriving on rich soils but tolerant of chalk, and not badly affected by late spring frosts (Bean 1976).

Paeonia delavayi became known to western botany in the 1880s through herbarium specimens collected in Yunnan by the missionary-botanist Père Jean-Marie Delavay. Delavay’s close collaborator in France, Adrien Franchet, named it in his honour, taking a specimen with very dark red flowers (Delavay 1142) as the type (Franchet 1886). Plants of this sort were first brought to Western gardens in the early 20th century, by George Forrest around 1910 (Stern 1946) and perhaps by Ernest Wilson under W 1333 of 1908 (Sargent 1913; Bean 1976).

As well as being geographically widespread and the only relatively common woody peony in the wild (Zhou et al. 2014), this is an extremely variable species which has vexed taxonomists (Hong 2010). It varies in height from almost 2 m down to 20 cm; there are even individuals in some populations whose woody stems are entirely underground, with only annual shoots above the surface. Petal colour ranges from red, through orange and yellow to white, with various types of bicolored flower known. There is significant variation in the breadth of the leaf lobes. A stoloniferous habit is very common, but the experience of cultivation is that this is far more apparent in some individuals than others. Low seed set and vegetative increase by stolons seems to be the norm in the wild (Hong 2010). In gardens, seed propagation has been usual, sometimes giving rise to novel colour combinations; the highly stoloniferous Potaninii Group is often divided (Bean 1976; Clarke 1988).

Taxonomists working outside China with limited material have attempted to categorise this variation in numerous unsatisfactory ways; several full species have been described, including P. lutea, P. trollioides and P. potaninii. More recently, thorough work by Chinese botanists involving population studies at numerous sites, suggests that while P. ludlowii is distinct, no infraspecific classification can meaningfully subdivide P. delavayi (Hong 2010 and references therein). A population genetic study using molecular characters confirms the distinctness of P. ludlowii; it further suggests that Tibetan populations of P. delavayi are diverging from those in Sichuan and Yunnan, but that this distinction is not reflected in the plants’ morphology (Zhang et al. 2018). Even in China, though, there is not unanimity: some workers still distinguish P. lutea and P. potaninii (Yang et al. 2020).

In cultivation it is important to have names for variants that are commonly grown, even if this is only because they reflect those points in the variation which happened to be introduced early. Names such as P. trollioides and P. potaninii are still seen, even though they might have little meaning in the context of wild plants. We choose to treat these variants as either botanical forms, where published, or as cultivar groups for which there are also precedents. This allows recognisable, horticulturally significant ‘high points’ in variation to be identified without requiring every individual to fit somewhere in a hierarchical classification. This is in contrast to the treatment of Haw (2001), adopted by some in Britain (Edwards & Marshall 2019), which divides the species into var. delavayi (height over 1 m) and var. angustiloba Rehd. & Wils. (height 1 m or less), then lists botanical forms within each variety; this seems to us to force a complex pattern of variation into an arbitrarily hierarchical scheme.

P. delavayi in its various forms is widely grown and offered by nurseries in western Europe and North America, although aerial stems are often killed in winter in colder parts of North America (Bremer 2019). An unusually broad range of variants, many of wild origin, is grown at RBG Edinburgh (Royal Botanic Garden Edinburgh 2020).

P. delavayi has not been a significant parent of hybrids in East Asia. From the early 20th century onwards, in Europe and especially North America, it has been hybridised with Central Plains and Japanese cultivars to produce an important group of garden shrubs, slighly comnfusingly known as the Lutea Hybrids; a couple of Irish hybrids with P. ludlowii are also known (for these see Paeonia Hybrid Cultivars Involving P. delavayi).