Hydrangea anomala D.Don

This deciduous climber is very similar to the familiar H. petiolaris, and in Western cultivation this scarce plant is best viewed by comparison with that garden stalwart. The general view has been that H. anomala is less hardy, less showy and perhaps less vigorous (Dirr 2021; Edwards & Marshall 2019; Foster 2023; van Gelderen & van Gelderen 2004), but this might not reflect untapped variation in this widespread Asiatic species.

H. anomala and H. petiolaris together belong to Section Calyptranthe, and their close relationship is confirmed by molecular studies (De Smet et al. 2015) although a thorough taxonomic study of the complex, using both molecular and morphological evidence and including all island populations, is much needed. The most reliable way to distinguish the two is stamen number, usually under 15 in H. anomala, over 15 in H. petiolaris (McClintock 1957). Their distributions are also distinct, H. anomala on the mainland (and Taiwan, but see taxonomic note above), H. petiolaris in Japan and on some Korean and Russian islands. In leaf H. anomala seems much more variable than H. petiolaris. An informal sample of herbarium specimens from across mainland China using the PlantPlus website (Chinese Academy of Sciences 2024) showed leaf shape ranging from narrowly elliptic/ovate to almost orbicular, often with a cuneate base not normally seen in H. petiolaris. Number and size of sterile flowers also varied considerably, although in cultivation H. anomala has a reputation for having fewer, smaller ones (Foster 2023). Garden literature (e.g. Bean 1981) often suggests a more domed inflorescence than the very flat heads seen in H. petiolaris, something relevant to older garden stocks but probably not diagnostic. In contrast to H. petiolaris, pink flowered plants turn up now and then; ‘Crûg Coral’ (see below) is one such, but seedlings from pink parents sometimes prove white (Foster 2023). 20th century experience has suggested that at least those forms more widely grown are rather less hardy than garden forms of H. petiolaris. Certainly, H. anomala is widespread both in warm southern China and at low altitudes to the south of the Himalayas, but this does not mean that there are not extremely hardy populations to be found somewhere in its vast range.

A conspicuous plant, H. anomala was clearly well known to various indigenous peoples. In southern Nepal it is recorded as grown on house walls and used as medicine as well as for ornament and firewood; decoctions are traditionally used to treat kidney and bladder stones, while bark paste is applied to wounds and burns, and the roots used against malaria (Singh 2016). In a neighbouring part of India it is used for animal fodder (Pant & Samant 2010), and leaves have been used in some way medicinally in China (Wei & Bartholomew 2001). It was described scientifically (Don 1825) from herbarium specimens collected in Nepal by the colonial era surgeon-botanist Nathaniel Wallich.

Bean (1981) gives 1839 as the date of introduction to Western gardens (probably to Kew), an early date which might imply Indian or Nepalese rather than Chinese origin. Ernest Wilson collected various specimens in Hubei and Sichuan (Sargent 1913), some of which were much more impressive in flower than cultivated plants of the day (Haworth-Booth 1984); seed from Hubei (under W 491, like most of the specimens) was established at the Arnold Arboretum, though now lost (Arnold Arboretum 2024). Of the many more recent collections, few stand out other than the two (below) given cultivar names. Some relatively widely distributed examples from across the wild range include SICH 1798 (Sichuan 1996, grown at Quarryhill, Howick and RBG Edinburgh), HNE 171 (N. Vietnam, 2014, grown at Logan among other places), DJHC 15119 (Hunan, 2015, nearly evergreen in the Puget Sound area, WA), HWJK 2065 (E Nepal 2002, sometimes evergreen at Crûg Farm, UK), BWJ 8052 (Emei Shan, Sichuan, 2000), and BSWJ 6804 (from an isolated population in NE Taiwan, 1999) (Quarryhill Botanical Garden 2024; Royal Botanic Garden Edinburgh 2024; Hinkley 2023; Crûg Farm Plants 2024).

Hardiness (probably along with lack of interest) has restricted its use in Europe to milder western areas. A record from Arboretum Kalmthout, Belgium shows roughly how far it has penetrated into more continental areas. Most North American records are from Pacific Coast gardens (e.g. Hoyt Arboretum 2024; University of Washington Botanic Gardens 2024; University of California Botanical Garden 2024). On the eastern seaboard there are plants from DJHC 15119 at the US National Arboretum (US National Arboretum 2024).