Erucic acid is a monounsaturatedomega-9fatty acid, denoted 22:1ω9. It has the formula CH3(CH2)7CH=CH(CH2)11COOH. It is prevalent in wallflower seed with a reported content of 20 to 54% in high erucic acid rapeseed oil, and 42% in mustard oil. Erucic acid is also known as cis-13-docosenoic acid and the trans isomer is known as brassidic acid.