Potamogetonaceae
Perianth segments 4 Potamogetonaceae
Inflorescence always 2-flowered. Carpels 2–19. Mature fruit usually stalked Ruppia
Peduncle at fruiting stage coiled several times. Flowers floating or close to the water surface. Fruit submerged
Leaves truncate or emarginate, 5–15 cm long, 0.5–0.8 mm wide. Carpels 2–6 usually 4. Peduncle at flowering more than 15 cm long. Fruit brown-black, asymmetric, 3–4 mm long; fruit stalk often reflexed. Coast. Lagoons and estuaries in brackish to very salt water. Fl. spring–autumn Ruppia megacarpa
Leaves obtuse or acute, 5–10 cm long, usually less than 0.5 mm wide. Carpels 4–12 but usually 6–8. Peduncle at fruiting stage usually more than 10 cm long. Fruit slightly asymmetric, 2–3 mm long. Coast. Lakes and lagoons in brackish to very salt water and usually in water less than 1 mdeep. Fl. spring–autumn Ruppia polycarpa