Global distribution of Hydatellaceae. The distribution is based on online herbarium resources  and new collection records; each collection locality is represented by a 120 km radial sweep. Five biogeographic areas are delineated by labelled ovals: India, New Zealand, northern Australia, south-eastern Australia, and south-western Australia. Species found in each area are listed; note that Trithuria submersa is treated here as south-eastern and south-western species. We created the map using ArcMAP version 9.3 (Environmental Systems Research Institute, Redlands, CA, USA); the projection is Lambert’s cylindrical equal area.