Ipomoea aquatica , known as `` water spinach '' , `` water morning-glory '' , `` water convolvulus '' , `` Ong-Choy '' , `` Kang-kung '' , or `` swamp cabbage '' , is used as a green vegetable . Ipomoea aquatica , known as water spinach , water morning-glory , water convolvulus , Ong-Choy , Kang-kung , or swamp cabbage , is popularly used as a green vegetable especially in East and Southeast Asian cuisines .