Symplocos Desf.

For the temperate gardener, Symplocos is an ‘iceberg genus’, only a few of whose species, if any, will float into consciousness. This is a shame; Tom Hudson, who has botanised extensively in east Asian forests rich in this genus and who gardens at Tregrehan in Cornwall, UK, where the mild winters and humid summers allow many trees from such areas to thrive, considers them ‘wonderful plants’ (pers. comm.). The scented flowers are usually white; the deeply-divided corolla lobes resemble petals (typically five) and the generally long and numerous white stamens create a haze above them, suggestive of the blossom of the unrelated family Myrtaceae; in Symplocos however, these flowers cluster in often architectural small towers or short spikes. If the flowers are fertilised – Symplocos have a reputation for being self-incompatible – berry-like fruit will follow, most characteristically in shades of electric blue.

In the nomenclature followed here, the genus occupies its own family, Symplocaceae, whose least distant relatives within the Ericales include the storax genus Styrax (Royal Botanic Gardens, Kew 2024). The genus was first described by Nikolaus Jacquin in 1760; its name derives from the Greek ‘joined together’ and describes the distinctive way that the base of each stamen attaches to the corolla.

Asiatic Symplocos species enjoy a multitude of uses in Chinese traditional medicine, to the extent that some species are threatened by over-harvesting, while their arrays of bioactive compounds increasingly interests medical science for their potential roles in cancer treatments and as phosphodiesterase inhibitors. Yellow and brown dyes are derived from the bark and leaves of several species, and the light, often soft timber is used in small-scale construction. Some Symplocos are being explored in China for biodiesel production, and the genus in general suffers from few pests and diseases, and tends to be tolerant of drought and soil salinity (Dakhil et al. 2024; Liu et al. 2017).

In temperate North America, a single species, Symplocos tinctoria (L.) L’Hér., is native to the south-eastern United States but as one of the less showy members of the genus is granted next to no garden space, while in Europe the only species at all likely to be encountered is S. paniculata Thunb., which in the broad sense adopted here is the genus’ only fully deciduous species, and which joins Clerodendrum trichotomum as the only tree northern gardeners can grow with sapphire blue berries. The subtropical bias in the distribution of Symplocos, the difficulties inherent in identifying many of its species, and a widespread lack of interest in the group as garden plants, all combine to make it unusually hard to confirm which other kinds are cultivated in our area, and which of these are successful or conspicuous enough to merit individual entries in this account. Doing well at Tregrehan in Cornwall, or at Caerhays Castle in the same county, are S. dryophylla C.B.Clarke, S. nokoensis (Hayata) Kaneh. and S. sumuntia Buch.-Ham. ex D.Don, all from the warmer parts of temperate east Asia.

The living collection of the Royal Botanic Garden Edinburgh is also rich in Symplocos, although the growing conditions this far north do not generally allow these plants to make successful outdoor garden features. S. cochinchinensis (Lour.) S. Moore is another species to be grown here, in the form of collections from Taiwan in 1993 and from Japan in 2008, at the northern edge of a vast and essentially tropical distribution that extends through to northern Australia (Royal Botanic Garden Edinburgh 2024). Species cultivated in the frost-free conditions of the University of California Botanical Garden at Berkeley include S. hartwegii A. DC., S. breedlovei Lundell and S. tacanensis Lundell, all collected at high altitude in Chiapas State in tropical south-eastern Mexico (University of California Botanical Garden 2024). Symplocos not yet identified to species level include a couple of plants at Tregrehan (T. Hudson pers. comm.), and, at Edinburgh, collections made in Nepal in 1989 and in Mexico from 1995–2006 (Royal Botanic Garden Edinburgh 2024). As a demonstration of the difficulties this genus can present, another arborescent Symplocos at Caerhays Castle, with a ‘black’ bark and a ‘fairly unpalatable scent’ to its clusters of creamy flowers, keys out in Wu & Nooteboom 1996 as S. lucida (Thunb.) Sieb. & Zucc. (Williams 2019); this name is accepted by Plants of the World Online (Royal Botanic Gardens Kew 2024), but this resource assigns many of the twenty-odd synonyms listed in Wu & Nooteboom 1996 to a total of eight other species (one of which is not a Symplocos at all). Meanwhile a thriving young tree at Tregrehan, 9.5 m tall in 2024 (Tree Register 2024), grown from seed collected by Tom Hudson from a plant also believed to have been S. lucida, has not yet flowered but from its foliage characteristics it now seems more likely to represent the unrelated laurel Dodecadenia grandiflora (T. Hudson pers. comm.).