Occurs in many plants e.g. Melilotus officinalis (sweet clover) Coumaric acid is a hydroxycinnamic acid, an organic compound that is a hydroxy derivative of cinnamic acid. There are three isomers, o-coumaric acid, m-coumaric acid, and p-coumaric acid, that differ by the position of the hydroxy substitution of the phenyl group. p-Coumaric acid is the most abundant isomer of the three in nature. (Wikipedia)

Trans-O-Coumaric Acid Health Effects