Acacia nigrescens

Botanical Name: Acacia nigrescens Oliv.

Synonym:  Acacia pallens (Benth.) Rolfe, A. mellifera sensu Henkel

Common Name: Knob Thorn

Plant Family: Mimosoideae, Fabaceae

Origin: Africa  

References: Coates Palgrave p. 292, Johnson p.73, Venter, p. 108. S.A. No. 178, Zimb. No. 215

Description: Medium to large deciduous tree with upward-tending branches, with a rounded or spreading crown but never flat topped. Trees stand bare for several months. Leaflets are almost circular, soft pale green. Thorns are small and hooked. Larger knob thorns on trunk, branches and stems. Flowers are spikes, at first rusty pink, then creamy white. Flowering occurs in early spring when the tree is leafless. Pods long and straight, brown and dehiscent.

Features of Particular Interest: Bark dark brown and knobbly but for young trees is yellowish and peeling on young twigs, with hook thorns. Flowering may be erratic.

Height and Spread: Up to 20m, but usually 8 – 10m, spread up to 8m.

Periods of Interest                                                    


Soil and Moisture: Grows on heavy clay soils. Easily grown from seed. Soak seed in hot water. Fast growing, up to 700mm a year. Flowering can be expected at about 12 years.

Aspect: Not critical but enjoys full sun.         

Hardiness: Drought resistant and can withstand cold but sensitive to frost.

Maintenance and Pruning: Not required.

Propagation: Cover seed lightly with sandy planting mixture and water regulary, but do not saturate the planting medium.

Problems and Drawbacks: Not known to have intrusive roots. Leaflets are shed in the dry months.

Use and Associated Planting: Cattle and various animals feed off the fallen leaves and pods. Pods are a favourite of the brown-headed parrot. Attractive as specimen in larger gardens, also good if planted in groups of 3 or 5 on lawn giving a bushveld feel to the garden. Has taproot and is not aggressive. Good bonsai specimen.trunks