The 25th July 2021 marks 400 years of botanical research and teaching by the University of Oxford.

As a celebration and count-down to this anniversary, the University of Oxford Botanic Garden and Arboretum, together with the Oxford University Herbaria and the Department of Plant Sciences, will highlight 400 plants of scientific and cultural significance. One plant will be profiled weekly, and illustrated with images from Oxford University's living and preserved collections.

Plant 100 The Raisin Tree / Hovenia Dulcis

Hovenia is a small genus of large, deciduous Asian trees. The generic name commemorates David ten Hove, a financial supporter of the eighteenth-century botanist Carl Peter Thunberg's botanical exploration of South Africa. Hovenia dulcis can grow to a height of over 20 m, producing clusters of self-fertile, inconspicuous, white flowers followed by seeds contained in small, capsular fruits. These capsules are supported on pedicels which swell as the fruit matures. The pedicels are edible and many of the plant's common names refer to these parts, for example, the Chinese chi-chao li, meaning 'chicken-claw pear'.

Hovenia dulcis is indigenous in eastern Asia but a long history of cultivation and subsequent naturalization has obscured its precise origins. Its relative scarcity in parts of its native range, such as northern Thailand, have led to its inclusion in reforestation projects. Ironically, in many areas to which it is not indigenous it has become an invasive species. Introduced to parts of South America and Africa as an ornamental tree, as well as a source of fuel and a fast growing windbreak and shade tree for livestock, it has become a problem in the seasonal deciduous forest of the Uruguay river basin (affecting Brazil, Paraguay, Argentina and Uruguay). It has proved similarly invasive in Tanzania. Hovenia has displaced sensitive native species in these environments but is difficult to eradicate, resprouting vigorously from stumps and exhibiting a high success rate in germination.

The swollen pedicels of Hovenia dulcis may be eaten raw, alternatively they maybe dried or processed to make beverages. They have a high sugar content, up to 23% dry weight, and a pleasant taste which has been likened to raisins. The difficulty of mechanical harvesting has limited their commercial value. In cool climates, such as that of the British Isles, the pedicels may swell but have insufficient heat to ripen.

Traditionally, the pedicels have been used for hangovers and the treatment of liver problems; they are mentioned in seventh-century Tang Dynasty materia medica. Modern research confirms that the flavanonol ampelopsin (dihydromyricetin), also found in the genera Ampelopsis and Cercidiphyllum, can reducing the symptoms of alcohol intoxication and withdrawal. This chemical also appears to have potential in the treatment of liver damage and liver cancer, whilst other investigations have focused on its potential for the treatment of osteoporosis. Extracts of Hovenia dulcis are available commercially, marketed as a remedy for the after-effects of excessive alcohol consumption.

Further reading

Reich L 2004. Uncommon fruits for every garden. Timber Press.

van Wyk B 2005. Food plants of the world. Timber Press.

James Penny