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the only genus of the family Salviniaceae—a family of aquatic heterosporous ferns. The plants are rootless annuals or perennials. The leaves are closely arranged on the rhizome in whorls of three: two are entire and floating, and one is sporiferous and dissected into narrow rootlike lobules, which are submerged in the water. Some of the interior segments of the leaves bear spherical sporocarps containing microsporangia and megasporangia. There are about ten species, distributed in tropical America and Africa and, to a lesser degree, in North America and Eurasia. The USSR has one species—S. natans.