A group of flavonoid pigments the members of which contain an unaltered *flavonoid
nucleus. It includes flavone, found in certain Primula species, and the more widespread apigenin and luteolin. Isoflavones are isomers of flavones in which the Β group of the flavonoid nucleus is attached to the third rather than second carbon of the central C3 group. Isoflavones are particularly common in the Leguminosae. Some isoflavones have oestrogen-like properties, which has led to sterility in sheep grazing on certain legume fodder crops, notably subterranean clover (Trifolium subterraneum).