A taxonomic study of the monotypic Heterozostera tasmanica (Martens ex Aschers.) Hartog concludes that four distinct taxa can be recognized within the genus. H. tasmanica is confined to Victoria and north and eastern Tasmania in Australia. The three new species have their own distributional ranges; Heterozostera nigricaulis is widely distributed in temperate Australia and Heterozostera polychlamys is restricted to Western Australia and South Australia, while Heterozostera chilensis occurs in Chile. The separation of species is based on a combination of morphological and anatomical characters, which include the presence or absence of generative shoots and wiry black erect stems, the anatomy of rhizomes and the morphology of leaf blade epidermal cells and blade apices. Heterozostera tasmanica and H. polychlamys produce distinct, determinate generative shoots bearing pronounced spathes, but do not possess wiry black erect stems. These two species differ in great detail in the morphology and in the anatomy of their reproductive and vegetative organs. In contrast, H. nigricaulis and probably also H. chilensis has indeterminate wiry black erect stems with a cluster of leaves at the top, but without normal generative shoots. Inconspicuous spathes sometimes form at the top of erect stems in H. nigricaulis. The detailed morphology of the erect stems and of the leaf blade epidermal cells of H. nigricaulis and H. chilensis is clearly distinct. Principal component analysis (PCA) on vegetative and reproductive characters support the recognition of four taxa in Heterozostera. This revision is presented with full descriptions, diagnoses, synonyms, a key, micrographs, illustrations, distribution maps, and an extensive bibliography. (c) 2004 Published by Elsevier B.V.