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eelgrasses, a family of monocotyledonous plants. They are perennial underwater sea grasses with creeping or thick tuberous rhizomes. The stems are flattened, and the leaves are linear and sheathed at the base. The flowers are unisexual or bisexual, without a perianth or with only a rudimentary one. The family comprises two genera and approximately 15 species that grow mainly in sand or silt and between rocks. Representatives of monoecious plants of the genus Zostera and dioecious plants of the genus Phyllospadix are found in the USSR (one species of the latter genus is found only in the Far East). All members of the family Zosteraceae are adapted for underwater fertilization.