Five new species and one new subspecies of Acacia from Western Australia are described, namely, A. clydonophora Maslin, A. disticha Maslin, A. durabilis Maslin, A. heterochroa Maslin (comprising subsp. heterochroa and subsp. robertii Maslin) and A. pygmaea Maslin. These taxa, together with four previously described species, A. celastrifolia Benth., A. myrtifolia, A. nervosa DC. and A. obovata Benth. comprise the informal "Acacia myrtifolia Group". A key to the species of this Group is presented. Brief notes on the variation in the Western Australian populations of A. myrtifolia are given. Acacia pawlikowskyana Ohlend. is treated as a synonym of A. myrtifolia (this name was formerly treated as a synonym of A. celastrifolia). Acacia acutifolia Maiden & Blakely is also regarded as conspecific with A. myrtifolia; it is likely that the type information published by Maiden and Blakely for this name was erroneous.