Most of us know the walnut by either the smooth, tan-colored, easy-to-crack type or the black walnut (Juglans nigra) native to North America with its rough and difficult-to-crack shell, but there are actually 15 species of walnuts native to Asia, Europe and the Americas. The English walnut originated in India and the regions surrounding the Caspian Sea. In the 4th century A.D., the Romans introduced the walnut to many European countries where it has been grown since. It is thought that the walnuts grown in North America were called English walnuts since they came to the U.S. via English merchant ships. Black walnuts and white walnuts are native to North America, specifically the Central Mississippi Valley and Appalachian area. They played an important role in the diets and lifestyles of both the Native Americans and the early colonial settlers. Today, the leading commercial producers of walnuts are the United States (specifically California), as well as Turkey, China, Iran, France and Romania. These tasty, nutritious nuts come from a beautiful ornamental tree that produces nuts for about 40 years and has a life span of about 60 to 80 years. The tree has many uses, including medicine, shelter, dye and lamp oil and, of course, food from the nut. The walnut kernel or nut consists of two partially attached bumpy lobes that are off-white in color and covered by a thin, light brown skin.