Peanuts and their shells. The peanut (Arachis hypogaea) is a native legume of South America which is now widely cultivated in warm climates. Large crops are raised annually in the United States. Much of the crop is roasted in the shell, or shelled and salted. Large quantities are ground for peanut butter, or crushed for peanut oil. Peanuts are a rich source of protein and oil, and they also contain vitamin B1 (thiamin).