Two species of Wolffia are known from Australia; these can be easily identified by means of the following key. I. Dorsal side slightly convex; ventral side laterally compressed, with a slight bulge below the budding pouch; width greatest in the dorsal plane.................. 1. W. australiana I. Dorsal side flat near the apex and convex near the base; ventral side globular; width greatest below the dorsal plane at ± half the height....................... 2. W. globosa