It grows in colonies that result from stems sprouting from roots. The bark is light brown and smooth on young plants.
Twigs are stout, angular, smooth, and covered with a whitish coat that can be wiped off.
Leaves are pinnately compound with 7-31 leaflets that are green on upper surface and nearly white on lower surface. Leaves turn red in autumn. The small, numerous flowers occur in much branched clusters. The fruit is a cluster of red drupes. Black walnut can be identified by slicing a stem to reveal a dark brown pith with air chambers.