Informations on root flavonoids have been extensively reviewed and their functional diversity critically appraised. Root flavonoids play significant roles in protecting the plants against pests and diseases, regulating root growth and functions, influencing different aspects of nitrogen cycle and exerting allelopathic growth effects. They also constitute an essential source of Pharmaceuticals. An exhaustive list of flavonoids which are of significance in relation to these properties has been compiled. A thorough understanding of the flavonoid composition, level, metabolism and regulation in the roots of various plants may help us in developing several applied topics. Safe and specific chemicals against root pests; chemicals regulating root growth and mineral nutrition; plant varieties resistant to root pests and adverse allelopathic effects; an improved nitrogen economy in agroecosystems; desirable varieties of medicinal plants, in whose roots flavonoids are the active principles; in vitro systems for flavonoid production obtained from root cultures, at a commercial scale. © 1990 The New York Botanical Garden.