The plants that live in water are called hydrophytes, e.g. Hydrilla, Vallisneria, and most of the algae. 

Many of the brown algae (Fucaceae) are used as staple food. 
Fucus vesiculosus, an edible brown seaweed 
Laminaria digitata, an edible brown brown alga 
Laminaria japonica, and edible brown alga.......may somewhere there is mistake as i m not a biologist so u confirm it