Mimosaceae - Thorn-Tree family
SA Tree 178
This tree prefers clay soils such as those found on basalts and in the valleys of granite landscapes. It is less common north of the Olifants River, occurring in low altitude woodland and wooded grassland, especially near rivers and lakes, but does not grow in river beds, or directly along permanent water. Tree sizes vary, from 8 -20 m, depending on habitat, and the largest trees are found in the flood-plains in all the Eco zones.
This is a very upright thorn-tree, with a straight, single trunk that branches high-up. The round, relatively narrow crown has a sparse canopy. There are woody knobs on the trunks of young trees, and on the large, young branches of older trees. The leaflet is large for an Acacia, giving the impression of a butterfly-type leaf. In early summer the knob thorn is the only tree to have masses of white flower spikes, and no leaves. The bark is typically dark brown, rough and fissured lengthwise, with knobs on younger trees. Stipules not spinescent, the small, hooked, blackish prickles are paired just below the nodes. I t is a deciduous tree, standing bare for several months in the year. They are fire and drought resistant. The sapwood is yellow, the heartwood dark brown, strong, tough and close-grained.
Links with animals - This tree is extremely vulnerable to animal damage. It is often attacked, sometimes killed, by wood borers. The tree seldom regrows after being pushed over or otherwise damaged by elephants. The flowers are eaten by baboon, monkey and giraffe. Leaves and shoots are eaten by kudu, elephant and giraffe. The pods are also eaten by giraffe. Holes in the trunk, and branches provide nesting sites for birds, with Whitebacked vultures often nesting on top of these trees.
Human uses - The wood is used for fence posts and also for walking sticks and knobkieries (fighting sticks). Poles are planted in the ground to act as lightning conductors, and the bark is used for tanning. It is difficult to saw and work with, but has been used to make furniture, and also for mining props.
Gardening - This will grow well in most gardens. It likes warm conditions, is susceptible to frost, but is fairly drought-resistant, The tree tends to drop thorny twigs, which would be a disadvantage in a family garden. It grows easily, but very slowly, from seed.
Leaves - Twice compound, opposite, roundish, with a smooth margin, There are normally only two pairs of leaflets per leaf. It is a particularly big leaf for an acacia. (Leaf 35 x 80 mm; leaflet 10 - 30 x 8 - 20 mm) Leaflets are often circular and are soft pale green or grey-green in colour.
Flowers - Spikes of white flowers cover the leafless trees in spring, August to September. Flowers are most plentiful after good, late summer rains. (80 mm)
Pods - Flat, bean-like pods hang down in clusters, They change from light green to brown as they ripen, November to April, and are rather thinly textured, without hairs, dehiscent, the remains of the calyx at the base of the pod also without hairs. January to June. Pods never open on the trees.(120 x 70 mm)
Thorns - Hooked thorns in pairs, grow far apart, on knobs.
Best places to see the Knob Thorn in Southern Africa:
The Knob Thorn is found in the Kruger National Park in the Mixed Bushwillow Woodlands, Pretoriuskop Sourveld, Malelane Mountain Bushveld, Sabie Crocodile Thorn Thickets, Thorn Veld, Knob Thorn / Marula Savannah, Riverine Communities, Olifants Rugged Veld, Stunted Knob Thorn Savannah, Mopane Scrubveld, Tree Mopane Savannah & Mopane / Bushwillow Woodlands ecozones.
 Tree species of Southern Africa >> Printable Tree List <<
South African Trees >> Printable Tree List <<
The Plant Kingdom (Plantae)
Wildlife - Fauna & Flora of Southern Africa
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