Investigations into the germination behaviour of seed of the widespread Australian arid zone leguminous tree Acacia aneura Benth. are described. Hardseededness has been overcome in routine laboratory studies, but attempts to understand the mechanism by which it is overcome in nature were unsuccessful. The seed germinates equally well in the dark and in the light within the temperature range 15-36°C. Temperatures between 20 and 30° are optimal for germination, and carbon dioxide concentrations up to 5 % increase the germination rate above that displayed in ambient air. A simple model has been developed which suggests that seed of this species should have been available and should have germinated in c. one year in every nine, since records began in parts of western New South Wales where mulga regeneration is absent.