Chlorella is a genus of single-celled green algae, belonging to the phylum Chlorophyta. It is found in fresh or salt water and in soil. It is spherical in shape, about 2 to 10 μm in diameter, and is without flagella. Chlorella contains the green photosynthetic pigments chlorophyll-a and -b in its chloroplast. It depends on photosynthesis for growth and multiplies rapidly, requiring only carbon dioxide, water, sunlight, and a small amount of minerals.
Chlorella has been researched as a potential food because it is high in protein and other essential nutrients. When dried, it is about 45 percent protein, 20 percent fat, 20 percent carbohydrate, and 10 percent various minerals and vitamins.
Chlorella, along with wheat grass, barley grass and spirulina, are sometimes referred to as "green foods." There are several species of chlorella. Those most commonly used in nutritional supplements are Chlorella vulgaris and Chlorella pyrenoidosa.