Black willow is a deciduous, rapidly-growing tree to about 20 metres tall with one, or less often up to four, trunks.

It is distinguished by its non-drooping habit and twigs which are shiny and red-brown when exposed to sun.

Other distinguishing features include thin leaves which are almost equally green on both sides and deeply fissured grey bark on stems more than 10 cm in diameter.

Black willow hybridises with other willows.

The trees can reach a height of 43 metres, with a trunk diameter of 1.2 metres.

Leaves are shiny light green above, duller below and often velvety along the midrib. They are narrow and taper pointed, with long, sharp curved tips and finely toothed margins.

Plants are male or female. Flower spikes are called catkins. Male catkins are yellow and female catkins are green. Catkins appear with leaves in spring.

Dispersal is by seed and to a lesser extent pieces. Black willows are prolific seeders, usually in spring; however seeds are viable for only about 24 hours.

Black willows were used to control erosion, but now cause channel diversions and choke streams.