Walnuts and pecans are closely related and share the same type of irregular nutmeat that is hard to peel. With the exception of fresh “wet” walnuts, the skin is left on for eating raw and cooking.
The most common species of walnut is the European, English or Persian walnut; the same species is known in the United States as the California walnut. Native only to America is the black walnut, a dark brown nut surrounding a rather astringent kernel; the texture is somewhat oily, good in cookies, cakes and ice cream. The milder white American butternut is also rich in oil, and it is used in cooking like the common walnut.