A major group of polyphyletic organisms of extremely varied morphology and physiology, mostly photosynthetic, but distinguished from plants by their complex form of sexual reproduction. They are freshwater and marine, terrestrial and subterranean; some are neustonic (living at the interface of water and the atmosphere). They live in various protozoa and within other plants. They live also in soil and on soil surfaces, on long-persistent snows, and in Antarctic rocks. Thermophilic algae inhabit hot springs. (From Webster, 3d ed; from Bold & Wynne, Introduction to the Algae, 2d ed, pp1-6).
