Hovenia acerba Lindley

Hovenia acerba was described by John Lindley in 1820 from a plant which had flowered and fruited the summer before in Aylmer Bourke Lambert’s greenhouse at Boyton Manor, Wiltshire, England (Lindley 1820). Lindley chose the specific name (‘bitter’) to contrast the fruit’s ‘austere flavour’ with that of H. dulcis (which he had probably been able to sample from the same greenhouse). But this fruit – eaten as early as August – was clearly immature, and the fruit of H. acerba as understood today does not differ signficantly in its qualities from that of H. dulcis; both ripen in early winter in the wild. Lindley also described the leaf of H. acerba as entire, but qualified this in the next edition of the Botanical Register. (In young plants the leaf can be almost untoothed, and H. acerba always tends to display more finely and closely toothed leaves than H. dulcis, but this feature can vary from tree to tree.) Lambert’s plant was supposed – improbably – to have been raised from a fruit imported from California, but Lindley did observe that it seemed similar to another in William Cattley’s greenhouse at Cattley Close, Barnet (now in north London), which was known to have come from seed from the Calcutta Botanic Garden in India. Francis Buchanan-Hamilton had introduced a Hovenia to this garden from Nepal, but this was supposed to have been introduced in turn from China (Sengupta & Safui 1984). The illustrations in Lindley (1820) show a style branching only near its tip, whereas the style of H. acerba, as now understood, characteristically branches below halfway (Nesom 2023). There is also the possibility of confusion with the predominantly Himalayan H. pubescens (treated by many authorities as a variety of H. acerba, var. kiukiangensis); just six years later, Robert Sweet named H. pubescens from another English greenhouse plant stated to have come from Nepal in or before 1823 (Sweet 1826).

These anomalies make it far from certain that true Hovenia acerba was really introduced to northern Europe in the early 19th century; in any case there is no evidence that either Lambert or Cattley had tried their plants out of doors. The inadequacies in Lindley’s description probably mean that H. acerba will remain subject to ongoing nomenclatural instability, but the name is, at least, now used for a taxon which seems to breed true and which differs in a few tiny but consistent features from H. dulcis (and from at least two other Chinese taxa).

By 1823, John Sims was already treating Lindley’s Hovenia acerba in synonymy with H. dulcis (Sims 1823). The tendency of subsequent authors such as Bean (1981) to do the same makes it hard to be at all sure of how much of a presence in cultivation H. acerba has really enjoyed; it certainly seems safe to assume that the majority of raisin trees cultivated in the west will be H. dulcis. Conversely, plants grown as H. acerba could potentially represent H. pubescens (syn. H. acerba var. kiukiangensis). Within China, the natural distribution of H. acerba overlaps significantly with that of H. dulcis but lies in general slightly further south, suggesting that some provenances at least might be harder to cultivate in cool, temperate gardens than H. dulcis – a plant which itself certainly prefers a continental climate with long hot summers.

In London, a plant labelled Hovenia acerba was introduced to the Chelsea Physic Garden in 1994, to feature in the garden’s commemorative John Lindley Walk. It is rather shaded, but enjoys a favourable microclimate where frosts are rare and where there is plenty of summer warmth; by 2016 it was 8 m tall (Chelsea Physic Garden 2024; Tree Register 2024). Another labelled tree has done rather better in the much cooler, oceanic climate of Holker Hall in coastal Cumbria, where it enjoys more room and was 8 m × 23 cm in 2024 (Tree Register 2024), slightly out-performing a nearby tree grown as H. dulcis. In these conditions, the latter sheds its foliage early in autumn while the H. acerba remains in full green leaf; in October 2024, the H. acerba also carried a reasonable crop of unripe fruit (Alan Hunton and John Killingeck pers. obs.). The origins of these two specimens are no longer known, although it seems reasonable to assume they are from the same source.

In the United States, a small tree in the National Arboretum, Washington D.C. (Hardiness Zone 7) was grown as Hovenia acerba in the 1970s, but had gone by 2024 (US National Arboretum 2024). Another tree 10.5 m tall grew at the J.C. Raulston Arboretum in North Carolina in 2000, but has also apparently been lost since (J.C. Raulston Arboretum 2024). The species remains available from seed in North America at least, while commercial propagation was underway in 2024 in France. The similarities shared by all Hovenia species make it rather unlikely that H. acerba will offer the temperate gardener anything which H. dulcis does not; but if it is slightly less happy, it should also be less likely to show any invasive tendencies.

‘Chinese Raisin Tree’ is sometimes suggested as a vernacular name, but is not particuarly apposite since this is one of at least four Hovenia native to China, where the ‘Japanese Raisin Tree’ H. dulcis is also at least as widespread.