Flavonoids constitute one of the most characteristic classes of compounds in higher plants.
However, their occurence is not restricted to flowers but include all parts of the plant. Both the oxidation state of the heterocyclic ring and the position of ring B are important in the classification. In isoflavonoids, ring B occupies position 3. Next to chlorophyll, anthocyanins are the most important group of plant pigments visible to the human eye. The anthocyanodins constitute a large family of differently coloured compounds and occur in countless mixtures in practically all parts of most higher plants.