Polyphenols are a diverse group of phytonutrients that determine colours of the fruits and vegetables, and protect the plants from diseases and invasion of external microorganisms. In fact, polyphenols are a part of defense mechanisms of the plants.
Polyphenols are classified into two major groups, flavonoids and phenolic compounds. A subtype of phenolic compounds is lignans, which are one of the major subclasses of phytoestrogens as well.
See “Flavonoids” and “Phenolic Compounds”.