A family of perennial, submerged, marine, monocotyledonous (see monocotyledon) herbs, with creeping or tuberous rhizomes, flattened stems, linear sheathing leaves, and unisexual flowers in vertical rows, borne within a leaf sheath on 1 side of the flattened stem. There is no perianth. Male flowers each consist of a single stamen with thread-like pollen grains. Female flowers consist of an ovary with 2 stigmas. Pollination occurs in the sea. Modern classifications recognize 3 genera, with some 17 species, found in most temperate seas.
Subjects: Plant Sciences and Forestry.