Plant 206

Ailanthus altissima (Mill.) Swingle (Simaroubaceae)


Tree of heaven

Ailanthus altissima is a quick-growing, deciduous tree native to China and Taiwan that can reach the height of fifteen metres in fewer than twenty-five years. Its rapid growth, and the perception that it grows to the heavens, gives the tree its common name.

Its attractive, large, pinnate leaves turn yellow in autumn, and superficially resemble those in the genus Rhus (sumac). One feature that readily separates Ailanthus leaves from those of the sumacs is the occurrence of glands at the base of each leaflet; on warm days these exuding sweet, sticky nectar. Ailanthus is also sometimes called the stinking sumac because of the acrid scent of all the plant's parts.

Ailanthus altissima is usually dioecious, meaning it has male and female flowers borne on separate trees. Small, green flower clusters in July are followed by red-tinged, winged fruit in the autumn. Both male and female trees are needed to produce viable seed, which can be produced in the warmer parts of southern England.

This plant, however, is far from heaven sent in many parts of the world. Indeed it is listed on many invasive species databases in North America and Europe due to its tenacious ability to grow rapidly and strongly, and to re-grow from the roots, if top growth is removed. It is a survival specialist.

It has been, and still is, commonly exchanged within the nursery trade since it was brought to Europe from China in the 1750s. It is, after all, a beautiful tree and was often used as a street tree in nineteenth-century Europe. Due to its horticultural popularity, Ailanthus altissima is proving to be more of an invasive weed in towns and cities; suckers can even push up through tarmac and disturb the foundations of buildings. Such traits have generated another name for the tree; tree of hell.

In its native China, Ailanthus altissima has been grown for many purposes. A tincture of its grey bark has been used for ailments such as baldness and malaria, and has been shown to slow heart rate. However, it has never entered western medicine. It has also been used to feed the larvae of the silkmoth Samia cynthia. This silkmoth produces a greater yield of silk than the well-known silkworm (Bombyx mori) but it is of an inferior quality. A yellow dye can be extracted from Ailanthus leaves, and the leaves and bark naturally produce an insect repellent.

Further reading

Kowarik I and Saeumei I 2007. Biological flora of Central Europe: Ailanthus altissima (Mill.) Swingle. Perspective in Plant Ecology, Evolution and Systematics 8: 207-237.

Rhoads AF and Block TA 2011. Invasive species fact sheet: tree-of-heaven. Morris Arboretum of the University of Pennsylvania.

Alison Quantrell