Prodr. 167 (1810) APNI
Roots long, pendent, without lateral rootlets. Plants ovate to fan-shaped, irregularly branched, to c. 2 cm across. Leaves triangular with rounded apex, surface more or less smooth; margins membranous, translucent. Microsporangial massulae spherical, with prominent barbs all over.
Widespread on still water or sluggish back waters of streams, but not found in alpine areas or in the mallee away from the Murray River.
Although treated as synonyms, there is morphological and molecular evidence to support the distinction of the American native Azolla filiculoides Lam. in which Victorian examples were formerly included, and A. rubra, an Australasian species (Reid et al., 2006).
Reid, J.D.; Plunkett, G.M. & Peters, G.A. (2006). Phylogenetic Relationships in the heterosporous fern genus Azolla (Azollaceae) based on DNA sequence data from three noncoding regions., International Journal of Plant Sciences 167(3): 529-538.