Walnuts are edible seeds taken from trees in the genus Juglans. The three species most commonly grown for their seeds are J. regia, originating from Iran, from which the Persian (or English) walnut is harvested; J. nigra, the black walnut tree, native to eastern North America; and J. ailantifolia, the Japanese walnut, also known as the heartnut. Numerous walnut cultivars have been developed commercially, nearly all of which are hybrids of the English walnut. They are often eaten as a snack, and can also be added to cooked meals, cereals and bread.Photograph credit: Ivar Leidus