Copeland (1947) assigned Pilularia L., Regnellidium Lindm. and Marsilea L. to the Marsileaceae and separated the genera on the basis of frond-form and the number of leaflets. In Pilularia L. the frond is filiform or grasslike, Regnellidium Lindm. and Marsilea L. are bifoliate and tetrafoliate respectively.