The structure and distribution of the flavonoids in plants

Over four thousand flavonoids, based on the C-6-C-3-C-6 skeleton, have been found in plants, and are divided into several classes, i.e., anthocyanins, flavones, flavonols, flavanones, dihydroflavonols, chalcones, aurones, flavan and proanthocyanidins, isoflavonoids, biflavonoids, etc. in this review, the chemical structures of the reported flavonoid classes are introduced and their distribution in nature are described. Additionally, some recent chemotaxonomical examples using the flavonoids are also given.