A wide range of aquatic plants have adapted to living in or under freshwater or salt water.  Macrophytes (emergent, submergent or floating aquatic plants) growing in water provide cover for fish, produce oxygen, provide food, remove excess nitrogen, and create substrate for invertebrates and plant roots. Aquatic plant tissue (aerenchyma) has air-filled spaces. Reeds are emergent plants, water lilies are floating, and milfoil is submergent. Aquatic plant tissue (aerenchyma) has air-filled spaces.