Quercetin

Quercetin is a plant flavonol from the flavonoid group of polyphenols. It is found in many fruits, vegetables, leaves, and grains; red onions and kale are common foods containing appreciable content of quercetin. Quercetin has a bitter flavor and is used as an ingredient in dietary supplements, beverages, and foods.

Quercetin is a flavonoid widely distributed in nature.The name has been used since 1857, and is derived from quercetum.It is a naturally occurring polar auxin transport inhibitor.

Quercetin is one of the most abundant dietary flavonoids,with an average daily consumption of 25–50 milligrams.

In red onions, higher concentrations of quercetin occur in the outermost rings and in the part closest to the root, the latter being the part of the plant with the highest concentration. One study found that organically grown tomatoes had 79% more quercetin than non-organically grown fruit.Quercetin is present in various kinds of honey  from different plant sources.

Reference.https://en.m.wikipedia.org/wiki/Quercetin