Quercetin is one of the most common and well-researched flavonoids.
Quercetin is a flavonol, which is a sub-category of flavonoids.
Flavonoids are phytochemical compounds in plants, fruits, herbs, vegetables and nuts. Humans cannot make quercetin in their bodies, but many fruits, vegetables, and drinks contain it.
Quercetin is a plant pigment (flavonoid). It's found in many plants and foods, such as broccoli, onions, peppers, buckwheat, capers, Brassica vegetables, apples, grapes, berries, tea, wine, many nuts and seeds.