Synopsis Seagrasses are marine plants belonging to two monocotyledonous families, Hydrocharitaceae and Potamogetonaceae. Being the only submerged marine angiosperms to have very successfully adapted to survive in the saline environment, these form a very fascinating group of plants. They are distinct from the members of the grass family Poaceae and should not be confused with them. Of the 52 species of seagrasses available in both tropical and temperate waters around the world, 14 species are found along the Coromandel coast (eastern coast of Peninsular India) extending to a length of about 2000 km. In India very few works have been carried out on these special groups of plants eventhough we have around 6000 km long coastal belt, consisting of many bays, gulfs, lagoons, estuaries and backwaters, abounding in rich wealth of seagrasses. Therefore, it was felt to be worth-while to make a detailed survey and study of the seagrasses of Coromandel coast. The present work is the result of such an exhaustive study conducted for the first time in India and contains detailed original descriptions, illustrations, ecological notes of all the species involved.