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DescriptionFree-floating aquatic plants. Rhizome slender, branched, roots absent or simple, borne singly or in fascicles. Leaves either dimorphic, borne in whorls of three (Salvinia) or alternate in 2 rows ( Azolla); veins free or anastomosing. Sporangia in thin-walled sporocarps on submerged leaves or in axils of submerged lobes; heterosporous.