The unusually dense clustering of knobs on the stem of this young Senegalia nigrescens tree underlines the variability of these trees. Some papery flaking of bark in its yellowish stage is still happening here. This is common on knob thorn branches in the 7 cm to 10 cm diameter range.
The thorns at the top of the knobs are small, recurving and black on old stems, reddish brown on new ones. Thorns grow in pairs on the knobs. They are characteristic woody, conical protrusions of irregular shape and size (Carr, 1976; Coates Palgrave, 2002).