Phenylpropanoids are a class of plant-derived organic compounds that are biosynthesized from the amino acid phenylalanine. This class includes: cinnamic acids, cinnamic aldehydes and monolignols, coumarins and flavonoids, stilbenoids. They have a wide variety of functions, including defense against herbivores, microbial attack, or other sources of injury; as structural components of cell walls; as protection from ultraviolet light; as pigments; and as signaling molecules.