Walk into your local grocery store and down the produce aisle, and you'll find a dazzling array of citrus, from navel oranges and clementines to grapefruit and key limes--and sometimes even more exotic fare like the Japanese yuzu or the baboon lemon. Nearly 100 million tons of citrus are produced globally every year, but where did these fruits first come from? How did they find their way into the Western world? And how did they become both a culinary...