Botanically speaking, all nuts are seeds, but not all seeds are nuts. Many dried seeds and fruits are called nuts, but true nuts are both seed and nut in one and cannot easily be separated.

Seeds are found in fruits and may be removed from them, as with almonds, cashews and pistachios. Botanists describe nuts as a simple dry fruit with one seed (sometimes two) in which the ovary wall becomes very hard (stony or woody), with the seed remaining unattached to that wall. True nuts include chestnuts, hazelnuts, pecans and walnuts. The other nuts widely used by bakers are described as culinary nuts or seed nuts. The distinction is only important in botany. Any large, oily kernel found within a shell and used in food can be considered a nut.

They come from all over the world. Almonds, hazelnuts, pistachios and English walnuts originated in the eastern end of the Mediterranean region. Today, however, the United States leads the world in almond production, with Spain a distant second. Still, 70% of the world’s hazelnuts grow along Turkey’s Black Sea coast, dominating the next two sources: Italy and the United States, specifically Oregon and Washington. Iran produces more pistachios than any other country, but the United States and Turkey supply the bulk of world trade in this variety. China grows the most walnuts, yet the United States — California, specifically — is the world’s largest exporter of them. Pecans and black walnuts, however, are native to North America. Georgia leads in pecan production, while black walnuts are still mostly gathered in the wild in the Southeastern U.S.