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knob thorn

The Knob Thorn is a slow-growing, deciduous tree that grows 5–18 m in height, with a long cylindrical shape and rounded crown. The common names in English and Afrikaans refer to the very characteristically knobbed thorns on the trunks and branches.

knob thorn bark

The knobs are very conspicuous, making the Knob-thorn tree easy to identify. Flowering is erratic and occurs between August and November.

knob thorn flowers

Flowers begin as 70-100 mm long elongated spikes of reddish-brown buds at the end of branchlets, turning creamy-white when fully open, totally transforming the tree. Rounded, butterfly-like double compound leaves form in late spring.

knob thorn leaves

The fruit is a long, thin pod about 100 mm long and 13-25 mm broad. They are initially a reddish-purple colour darkening to a dark brown and fall to the ground before they split open.

knob thorn seeds

Knob thorn is a species with a wide distribution range, occurring from Tanzania southwards to KwaZulu-Natal. They grow in various savanna regions, often at low altitudes, and in rocky areas, on well drained soil. It is drought- and termite-resistant. Although the Knob-thorn is very thorny, it is a highly nutritious tree, with the thorns merely limiting the amount of time animals feed on it.

Elephants eat the branches, leaves and shoots, kudu browse the leaves and shoots and giraffe, monkeys and baboons eat the flowers. Knob Thorn flowers are a dietary component for giraffes. Its flowers contain almost three times as much condensed tannin as leaves. Giraffes consume large quantities of flowers resulting in distinct browse lines on the trees. Giraffes have a very unique relationship with this acacia species – it is believed that they pollinate the trees.

Written By: Honorary Officer uMkhuze Game Reserve