Vachellia

Vachellia is a genus of thorny or spiny trees and shrubs in the Fabaceae or pea family. Some of the plants sprawl or climb. The genus is commonly known as thorn trees, previously acacias. The Acacia genus included Vachellia, Senegalia and more genera until about a decade into the twenty first century.

The stem spines or thorns may be long or only short prickles, straight or curved, paired or not and sometimes inflated or thickened. The alternate leaves are bipinnate, the leaflets small.

The flowerheads are spherical, yellow or creamy white, growing solitary, in short racemes or fascicled from leaf axils. There is usually a tiny, bell-shaped calyx. The four or five petals are usually united, absent from some species. The flowers are mostly bisexual, while unisexual ones are sometimes seen for instance in Vachellia nilotica.

The numerous stamens are exserted. The ovary is sessile or stalked, the style thread-like. Various solitary and social bee species are important in the pollination.

The fruits are bivalved pods that may dehisce. The pods may be broad or narrow, long or short, curved or straight and hairy or not. The compressed seeds have fleshy funicles or ovule stalks.

There are about 163 Vachellia species, 83 of which in Africa and some associated islands. The plant in picture is V. nilotica (Coates Palgrave, 2002; Leistner, (Ed.), 2000; Wikipedia).