decurrens is normally an erect tree 5-15 m tall but sometimes attains 20-22 m under favorable conditions.Branching tends to be lateral and crown spread is up to 8 m across on the largest specimens.

The bark is smooth, dark gray to almost black and may be fissured on mature plants. The bipinnate leaves are dark green and glossy. The inflorescence of A. decurrens is a raceme or panicle of globular flower heads. The pods are linear, brown, red-brown or dark brown to black, almost flat.