1. Bates, V.M., 1980. Re-evaluation of the Taxonomy of North American Azolla Based on Megasporocarp Morphology. M.S. Thesis, Memphis State University, Memphis, TN, 40 pp.
2. Azolla filiculoides new to the Southeastern United States;Bates;Am. Fern J.,1981
3. Azolla species from the Pleistocene of the Central North Sea area;Bertelsen;Grana,1972
4. Sporocarp structure in the heterosporous water fern Azolla mexicana Presl;Calvert;Scann. Electr. Microsc.,1983
5. Collinson, M.C., 1991. Diversification of modern heterosporous pteridophytes. In: Blackmore, S., Barnes, S.M. (Eds.), Pollen and Spores. Clarendon Press, Oxford, pp. 119–150.