Vachellia is a genus of flowering plants in the legume family, Fabaceae, commonly known as thorn trees or acacias. It belongs to the subfamily Mimosoideae. Its species were considered members of genus Acacia until 2009. Vachellia can be distinguished from other acacias by its capitate inflorescences and spinescent stipules. Before discovery of the New World, Europeans in the Mediterranean region were familiar with several species of Vachellia, which they knew as sources of medicine, and had names for them that they inherited from the Greeks and Romans. The wide-ranging genus occurs in a variety of open, tropical to subtropical habitats, and is locally dominant. In parts of Africa, Vachellia species are shaped progressively by grazing animals of increasing size and height, such as gazelle, gerenuk and giraffe. The genus in Africa has thus developed thorns in defence against such herbivory. The members of Vachellia are trees or shrubs, sometimes climbing, and are always armed. Of the 163 species currently assigned to Vachellia, 52 are native to the Americas, 83 to Africa, Madagascar and the Mascarene Islands, 32 to Asia and 9 to Australia and the Pacific Islands.

Vachellia tortilis, previously known as Acacia tortilis and commonly known as Umbrella Thorn in English and Haak-en-Steek in Afrikaans is widely distributed over the warm, dry parts of the northern and eastern parts of South Africa. It has the classic, umbrella-shaped canopy associated with thorn trees. It reaches heights of between 5-20m in nature. Flowering is profuse and occurs from November-January in the southern hemisphere. The flowers are white to pale yellow. The species adapts well to garden conditions, provided it does not receive too much water. It tolerates moderate frost and much drought. This truly makes an outstanding bonsai specimen!!