MARSILEACEAE

only family of the fern order Marsileales. The three genera and about 70 species of small aquatic ferns root in mud or grow in shallow water. The family is typified by spore-bearing structures (sporangia) in hard cases (sporocarps) produced at or beneath ground level at the bases of the leaves. The genera are widely distributed. Marsilea (water clover), with 60 species, has clover-like leaves with four leaflets. Pilularia (pillwort), with six species, has threadlike (filiform) leaves without leaflets. Regnellidium, with one species, has leaves with two leaflets.