Chlorella (Chlorella vulgaris) is a unicellular freshwater green microalga in the Chlorellaceae family found in freshwater habitats around the world. Unlike a typical leafy herb, it is microscopic and is cultivated in water-based systems rather than soil. The dried whole algae biomass is the material most commonly used in foods and supplements.

Chlorella is better known through modern nutritional and natural food traditions than through older household herbals. It is commonly added to powders, tablets, smoothies, and green food blends, where it is valued for its deep green color and concentrated whole-food character rather than for a long history of classic Western folk use.