False acacia or black locust tree

Quick facts

• Scientific name: Robinia pseudoacacia
• Family: Leguminosae. This tree is a member of the pea and bean family.
• Place of origin: eastern USA
• Conservation status: common
• Date planted: 1762
• Height: 17.1 m

About Kew's false acacia

This is one of the few trees remaining from the botanic garden founded at Kew in 1759 by Princess Augusta, the mother of George III. It is one of a group planted around the Temple of the Sun. It still holds some surprises – in 2009 Kew scientists studied it afresh and discovered four new biological compounds that had not been described before scientifically, and which may have unknown uses and human health benefits. Kew’s false acacia is also home to the Chief Gnome in the CBBC cartoon Gordon the Garden Gnome.

Take a closer look

• Look at the small 'leaves' – these are actually groups of 'leaflets', 15 or so making up what botanists technically refer to as a leaf.
• Each leaf usually has a pair of thorns at the base, which are bigger (up to 2 cm long) on younger growth. These – and the leaves' habit of drooping at night, like the acacia – are probably the source of the 'false acacia' common name.
• Without the metal bands this ageing tree might split apart as its trunk is about 75 % dead. With measures like this we could hope to keep it alive another 50 years or so.

Tree biology

The white, pea-like and vanilla-scented flowers of the false acacia are a major source plant for honey in the USA and France. It is very drought resistant. In fact it grows better when water is scarce. It is valued for its hardness and strength, and makes excellent firewood that burns slowly, with little visible flame or smoke. This species also has nitrogen-fixing bacteria on its root system. For this reason it can grow on poor soils and is an early colonizer of disturbed areas.

Cultivation and uses

The false acacia's wood is so hard that it makes ideal, rot-resistant fence posts, panelling, furniture and boats. In the 1800s it was an important shipbuilding wood, only bettered eventually by iron. As a young man, Abraham Lincoln famously split rails and fence posts from false acacia logs. Today, it is the most rot-resistant local tree in some parts of Europe and conservation projects have started to limit the use of tropical wood by promoting this tree and creating plantations.