Hovenia dulcis (Japanese Raisin Tree)

Scientific name

Hovenia dulcisThunb.

Synonyms

Hovenia inequalis D.C.; Hovenia acerbaLindl.

Common names

Japanese raisin tree

Family

Rhamnaceae

Origin

The origin of Hovenia dulcis is difficult to ascertain, but it is likely to be in temperate parts of Asia.

Naturalised distribution (global)

Locations within which Hovenia dulcis is naturalised include South American rainforests, USA, Australia, New Zealand and Central Africa.

Introduced, naturalised or invasive in East Africa

In East Africa, Hovenia dulcis is invasive in parts of Tanzania (Tropical Biology Association 2010). The editors found no records of its occurrence in Kenya or Uganda, though this does not necessarily mean that it is absent from these countries.

Habitat

Forest edges and gaps

Description

Hovenia dulcis is a deciduous, trees up to 10 m tall, sometimes (rarely) a shrub. It is a very smooth (almost glabrous) tree.

Leaves of H. dulcis leaves are membranous, broadly ovate (egg-shaped in outline with broad end at base), large (8-15 cm long, 6-12 cm wide), short-acuminate, rounded to shallowly cordate (heart-shaped) at base, with obliquely triangular obtuse teeth, green and glabrous (hairless) on upper side, pale green and glabrous to thinly pubescent (hairy) on nerves beneath, becoming deep brown when dry. Leaf stalk (petioles) 2.5-6 cm long.

The trees bear clusters of small cream-coloured hermaphroditic flowers. Fruits are red/brown drupes, about 7 mm across, containing 2 to 4 seeds. Plants begin to produce fruit after three or four years. The fruit is sweet, fragrant and is edible raw or cooked. Dried fruits look and taste like raisins.

Reproduction and dispersal

Reproduction of Hovenia dulcis is by seeds which are spread mainly by birds, but also by many other animals. Plants begin to fruit when they are 3-4 year old.

Economic and other uses

Hovenia dulcis has been introduced by humans for use as a timber tree and for its edible fruit. An extract of the seeds and young leaves can be used as a substitute for honey.

Environmental and other impacts

Hovenia dulcis rapidly invades disturbed forest, forming dense stands, inhibiting the growth of native plant species. It is hard to control spread due to the abundance of many different dispersal agents.

Management

The precise management measures adopted for any plant invasion will depend upon factors such as the terrain, the cost and availability of labour, the severity of the infestation and the presence of other invasive species. Some components of an integrated management approach are introduced below.

The best form of invasive species management is prevention. If prevention is no longer possible, it is best to treat the weed infestations when they are small to prevent them from establishing (early detection and rapid response). Controlling the weed before it seeds will reduce future problems. Control is generally best applied to the least infested areas before dense infestations are tackled. Consistent follow-up work is required for sustainable management.

Hovenia dulcis can be cut or dug out, but this is rarely effective as the plant sprouts vigorously when cut and resprouts from seeds in the soil. Effective control requires a combination of mechanical and chemical control methods. Application of a suitable herbicide to cut stumps is effective. When using any herbicide always read the label first and follow all instructions and safety requirements. If in doubt consult an expert.

The editors do not know of any biological control programmes targeted at this species.

Legislation

Not listed as a noxious weed by the state or governments in Kenya, Tanzania and Uganda.

References

PROTA database. Prota4U- Hovenia dulcis Thunb. www.prota4u.org/protav8.asp?h=M4&t=Hovenia,dulcis&p=Hovenia+dulcis. Accessed February 2011.

Tropical Biology Association (2010). Usambara Invasive Plants - Amani Nature Reserve - www.tropical-biology.org/research/dip/species.htm.

University of Alabama online datasheet on Hovenia dulcis - Japanese Raisin Tree. www.uah.edu/admin/Fac/grounds/RAISINTR.HTM. Accessed February 2011.

Editors

Agnes Lusweti, National Museums of Kenya; Emily Wabuyele, National Museums of Kenya, Paul Ssegawa, Makerere University; John Mauremootoo, BioNET-INTERNATIONAL Secretariat - UK.

Acknowledgments

This fact sheet is adapted from The Environmental Weeds of Australia by Sheldon Navie and Steve Adkins, Centre for Biological Information Technology, University of Queensland. We recognise the support from the National Museums of Kenya, Tropical Pesticides Research Institute (TPRI) - Tanzania and Makerere University, Uganda. This activity was undertaken as part of the BioNET-EAFRINET UVIMA Project (Taxonomy for Development in East Africa).

Contact

BioNET-EAFRINET Regional Coordinator: eafrinet@africaonline.co.ke