A rare, new tetraploid Atriplex, restricted to two populations ∼30 km apart in arid Western Australia, is supported as a distinct species by morphological and molecular evidence. Genetic analyses using amplified fragment length polymorphisms (AFLPs) showed significant genetic divergence between the two populations. In contrast, an ordination based on elliptic Fourier descriptors for leaf and bracteole shape did not identify any consistent morphological differentiation. Although the level of genetic differentiation is similar to that previously reported between subspecies in other Atriplex, the populations of the new taxon are described herein as A. yeelirrie K.A.Sheph. & K.R.Thiele, without taxonomic recognition at the intraspecific level. We outline our reasoning for this decision and discuss the implications for appropriate conservation management of the species, structured into two genetically distinct populations.