Answer:
Air-filled tissues in various parts of the plant provide the buoyancy that allows them to float. ... A similar but invisible air-filled tissue is found in the swollen leaf stalks of the water hyacinth,Eichhornia crassipes.
Another free-swimming aquatic plant, the water lettuce or Pistia stratiotes, is covered with fine water-repellant hairs that trap air. The leaves of the water lettuce are arranged in rosettes that do indeed make it look much like a small head of lettuce. Leaves can also float by themselves.
