New and existing collections of Batrachospermum pseudogelatinosum Entwisle & Vis, and related taxa, from Australia and New Zealand, were analysed to determine whether this morphologically diverse taxon should be further subdivided. In particular, the value of the taxonomic character 'dioecy/monoecy' was assessed with molecular (rbcL gene sequences), morphometric and diagnostic morphology datasets, and its applicability more widely within the genus considered in light of our results. While the rbcL sequences supported our intuitive feeling that there is great variability within this taxon, there was no practical way to subdivide B. pseudogelatinosum. We recommend the acceptance of a broadly circumscribed paraphyletic species (paraspecies), B. pseudogelatinosum, which includes both dioecious and monoecious populations. The value of monoecy/dioecy as a character must be determined on a taxon-by-taxon basis—it is no better or worse than any other taxonomic character. Batrachospermum pseudogelatinosum occurs in eastern Australia and Stewart Island in New Zealand, with implications for the circumscription of B. campyloclonum Skuja ex Entwisle & Foard.
Extensive variation in evolutionary rate of rbcL gene sequences among seed plants.
