Stamens consisting of 2 free, bilocular, extrorsely lengthwise dehis-cent, deciduous thecae connected by a ridge-like connective; Fruit ovoid or ellipsoid with scarious pericarp or else crescent-shaped with the pericarp differentiated into a soft exocarp and a hard fibrous en-docarp. Seed 1, ovoid or ellipsoid;
Asia-Tropical, northern and southern hemispheres present
Three genera with together 17 species distributed in the temperate seas of the northern and southern hemispheres, the area of a few species extending into the tropical waters. In Malesia only one genus with one species.
In the past this family has been considered a subfamily or tribe of the heterogeneous family Potamogetonaceae (Ascherson 1907; Markgraf 1936; Eckardt 1964; Den Hartog 1970). Tomlinson (1982), who made a thorough study of all helobian families came to the conclusion that the Zosteraceae form a clearly circumscribed group whose affinities with other helobian families are obscure, and maintained them at family level.