The tree grows up to 15 m in height, with rough, dark, red-brown to blackish bark. The trunk is usually branched relatively close to the ground.
Paired and straight conspicuous white spines occur, especially on the lower branches and on younger trees or trees being browsed by animals although some forms are almost thornless as adults.
Trees often flower after rain and are usually in full flower in spring and early summer. The flowers are arranged in heads and exude a sweet scent.
The slender, sickle-shaped pods split open from January onwards releasing small, hard seed. 

Reference:

1 PlantZAfrica - Acacia karroo