A family of highly specialized aquatic or semi-aquatic ferns. The rhizomes bear alternate leaves which are either cylindrical and taper to a point, e.g. Pilularia, or bear 2 or 4 broad leaflets at their tips, e.g. Marsilea and Regnelidium. The sporangia are of two kinds, megasporangia and microsporangia, and are borne in globose, hairy sporocarps at the base of the leaf stalks; 2 or more sori occur in each sporocarp, and each sorus contains both types of sporangium. There are 3 genera, two of which are almost cosmopolitan, and some 70 species.
Subjects: Plant Sciences and Forestry.