Leaves distichous. ‘Flowers’ without perigone, solitary, either terminal on a short branch or arranged in a cymose inflorescence (Syringodium). Ovule 1, sub-orthotropous, pendulous. Fruit either with a stony pericarp, more or less compressed (Cymodocea, Halodule, Syringodium) or with a stony endocarp and a fleshy exocarp from which 4 cuneate spreading lobes grow out (Amphibolis) or consisting of a fleshy bract which encloses the fertilised ovaries (Thalassodendron); Seed 1.
Asia-Tropical, Australian temperate waters present, extending into the subtropical and warm-temperate waters present, tropical seas present
Four genera with together 14 species, distributed in the tropical seas, some species extending into the subtropical and warm-temperate waters The fifth genus, Amphibolis with 2 species, is limited to the Australian temperate waters In Malesia 4 genera.
In the past this family was considered a subfamily or tribe of the heterogeneous family Potamogetonaceae (Ascherson 1889, 1907; Markgraf 1936; Eckardt 1964; Den Hartog 1970). Following Tomlinson (1982) the Cymodoceaceae are now regarded as a family of its own. This view has been shared by Dahlgren et al. (1985) in their survey of the families of Monocotyledons. Hutchinson (1934) has classified the genera here presented as belonging to Cymodoceaceae within the family of the Zannichelliaceae. Although Tomlinson regards this as inappropriate, the combination of the two families is not unlogical, but as Zannichelliaceae s.s. do not occur in Malesia this subject will further not be discussed.