We describe a new species in the endemic Australian mite genus Acroseius Błoszyk et al., 2005. Acroseius weirisp. nov. is distinguished from the other two species in the genus by the presence of a row of greatly expanded leaf-like setae on the caudal margin of the idiosoma. New locality records substantially increase the known range of the other two species, A. tuberculatus and A. womersleyi. The three species show disjunct distributions on the east coast of Australia, each species associated with a different forest type and climate. This appears to be the result of geographic speciation associated with increasing aridity and habitat fragmentation.