Cereal grass is the young green plant that grows to produce the cereal grain. Grasses belong to the Gramineae family that provides all the world's cereals and most of the world's sugar. Wheat grass and barley grass are popular nutritional supplements. These cereal grasses, along with spirulina (see Spirulina), chlorella (see Chlorella), oat grass and alfalfa are sometimes referred to as "green foods." Wheat grass and barley grass are rich sources of chlorophyll (see Chlorophyll/Chlorophyllin), which is believed to have some health-promoting activities.