Family MimosoideaeAcacia nigrescens is a deciduous, small to medium-sized tree which occurs in various savanna regions, often at low altitudes, and in rocky areas, on well drained soil. It is drought- and termite-resistant.
The knob thorn is a deciduous tree that grows 5–18 m in height, with a long cylindrical shape and rounded crown. It has knobs on the trunks and on branches with persistent thorns arising on the knobs. The trunk is approximately 0.5 m in diameter on mature specimens but can reach 0.75 m. Thorns are in pairs below the leaves. The leaf consists of 2 or3 pairs of pinnae (primary divisions of a compound leaf) with 1 or 2 pairs of leaflets per pinna. Flowers are yellowish white in elongated spikes during Aug.–Nov. They appear before or with the new leaves making the tree very conspicuous. Fruit are dark brown, thinly textured pods borne in pendant (hanging downward) clusters.
Uses and cultural aspects
Knob thorn trees are the host of hole-nesting bird species and the larvae of the dusky charaxes butterfly. The wood is hard and drought- and termite-resistant but frost-tender; it has been used to make fence posts and mine props. The knob thorn yields good quality firewood producing lasting coals and severe heat. It also makes a good bonsai subject. It is not regularly used for furniture because it is difficult to cut. Knob thorn leaves and pods are included in the diet of elephant, giraffe, kudu, duiker, impala and steenbok.