A contradictory species, loved by some and despised by others: it has attractive fragrant blossom yet vicious spines, restores damaged soils yet is sometimes invasive. Its common names, Robinia and False Acacia, both echo its scientific name (pseudoacacia). Introduced c.1634.
Native to the south-eastern USA, growing in mixed forests with Black Walnut and Tulip-tree. Widespread across many countries, including Hungary, where it makes up 25 per cent of forest cover. Fairly commonly naturalised in central and southern England but uncommon elsewhere in Britain and Ireland; park, garden and street specimens are usually cultivars.
Monoecious, producing pea-form flowers that are insect-pollinated. Seeds produced in bean-like pods (10cm), but main form of reproduction is vegetatively via root suckering.
Medium (to 30m), often multi-stemmed with a round domed crown, the branches steeply ascending then arching outwards. Bark dark brown, becoming deeply vertically fissured. Twigs bear paired sharp spines (25mm, modified stipules), especially on young lower shoots and suckers. Leaves 15-25cm, compound pinnate with 9-23 smooth-margined leaflets that fold in wet weather and at night. Flowers white (20mm) in fragrant pendulous racemes (15cm). Fruit a flattened, glabrous, winged-seam legume with 4-10 seeds. Honey Locust differs: triple spines, sometimes bipinnate leaves, green flowers, fat pulpy pods.
Short-lived (60-100 years), intolerant of shade and high-forest competition, growing best on woodland edges and in clearings. Caution is needed when planting it in woodland, given its invasive tendency on the European mainland, though cooler Britain and Ireland seem to keep it in check. Pruning for valuable timber is worthwhile but tricky given its steep branch angles, and it can be coppiced. Despite its tough, spiny appearance it is sensitive to late spring frosts, drought and waterlogging, and fairly easily wind-damaged, though highly tolerant of urban pollution and good at colonising pavements and waste ground. Its nitrogen-fixing root nodules help regenerate degraded soils. Popular street cultivars include the compact thornless 'Bessoniana' and the golden-leaved 'Frisia'.
No special associated biodiversity, although bees visit its flowers for pollen and nectar.
Generally a healthy species. Under a warming climate could become invasive in warmer parts of England.
Timber is hard and highly durable for outdoor furniture, playgrounds and fenceposts. ‘Acacia’ or ‘Locust’ honey is usually made from the nectar of this species, especially in Hungary.
