The Juncaginaceae is a small cosmopolitan family of usually aquatic herbs. Current world wide reviews of the family list approximately 12 species and 4 genera in the family with the centre of diversity in South America. In Australia the family is considerably more speciose than previously recognized. Taxonomic and ecological studies in Eastern Australia have shown that there are 12 perennial taxa present in freshwater environments. Recent ecological and biological studies in south Western Australia have established that at least 15 annual taxa are present, many of which are endemic to this area. These findings clearly establish Australia as the world centre for species diversity in the family. The eastern and western perennial taxa are aquatic, wind pollinated, largely outbreeding with a high degree of polyploidy present. The Western Australia taxa are mainly small, effectively terrestrial annuals of winter damp sites. These taxa are usually diploid, wind pollinated, capable of inbreeding and frequently occur in naturally saline sites. Their small size enables large populations to be present in micro-habitats and often several taxa co-occur. Most members of the annual group have specialized epizoochorous fruits, compared to the water-dispersed fruits of the perennials. The phytogeography of the family is compared to other speciose monocotyledon families (Anthericaceae, Centrolepidaceae, Cyperaceae and Restionaceae) of Western Australia.