Chlorella, genus of green algae (family Chlorellaceae) found either singly or clustered in fresh or salt water and in soil. Chlorella has been extensively used in photosynthetic studies, in mass cultivation experiments, and for purifying sewage effluents. Because the algae multiply rapidly and are rich in proteins and B-complex vitamins, several species have also been studied as a potential food product for humans both on Earth and in outer space. Chlorella is sometimes used as a vegan nutritional supplement.
The algal cell is roughly spherical and features a cup-shaped chloroplast and numerous starch grains. Members of the genus reproduce asexually by nonmotile reproductive cells (autospores) that rupture through the mother cell. Those cells sometimes cling together to form a new colony.