EARTH SCIENCE > BIOSPHERE > ECOSYSTEMS > AQUATIC ECOSYSTEMS > PLANKTON > PHYTOPLANKTON
Phytoplankton is the plant portion of the plankton, the plant community in marine and freshwater situations, that floats free in the water and contains many species of algae and diatoms.
Krebs, Charles K. Ecology - 4th ed. 1994. HarperCollins College Publishers, New York, New York.