It is usually an erect tree with smooth bark, bipinnate leaves and spherical heads of fragrant pale yellow or cream-coloured flowers followed by black to reddish brown pods.

Acacis mearnsii is a spreading shrub or erect tree that typically grows to a height of 10 m (33 ft) and has smooth bark, sometimes corrugated at the base of old specimens.

An analysis of genomic and chloroplast DNA along with morphological characters found that the section is polyphyletic, though the close relationships of many species were unable to be resolved.

In Africa, A. mearnsii competes with local vegetation for nitrogen and water resources, which are particularly scarce in certain regions, endangering the livelihoods of millions of people.

Other woodland species can rapidly use these increased nitrogen levels provided by the nodules of bacteria present in their expansive root systems.

The rare Tasmanian hairstreak butterfly lays her eggs in these cracks, which hatch to produce caterpillar larva attended by ants (Iridomyrmex sp.)

[citation needed] A. mearnsii is used similarly as a larval host plant and food source by the imperial hairstreak, Jalmenus evagoras.

[20] The tree is home to various grubs, such as wood moths, which provide a food source to black cockatoos, which strip the bark for access to these borers.

These creatures provide an important predatory role to deal with tree dieback caused by scarab beetles and pasture pests.

These "hill-topping" sites are critical habitat for male butterflies to attract females for mating, which then lay their eggs under the wattle's bark elsewhere but still within close proximity.

However, a "wattle seed-eating insect" which enjoys liquid meals using its proboscis-like injector to pierce the testa and suck out the embryo, often reduces the seed's viability.

[23] The Ngunnawal people of the Australian Capital Territory use the gum as food and to make cement (when mixed with ash), and to ensure a supply of sap, the bark was cut in the autumn.