Worldwide, tropical to temperate regions.
Azollaceae has been included in Salviniaceae, but the relationship is not close.
In this treatment, "upper lobe" refers to the emersed lobe and "lower lobe" refers to the immersed lobe. Developmentally, the emersed lobe is actually abaxial and the immersed lobe is adaxial. To facilitate identification in the field, however, the terms describe the appearance of the lobes to the viewer, not the development of the lobes.
Genus 1, species ca. 7 (3 species in the flora).