By Harold McGee
Beans and peas belong to the third largest family among the flowering plants (after the orchid and daisy families), and the second most important family in the human diet, after the grasses. The distinctive contribution of the legumes is their high content of protein, two to three times that of wheat and rice, which they develop thanks to their symbiosis with certain soil bacteria. Species of Rhizobium bacteria invade the roots of legume plants and convert abundant nitrogen in the air into a form that the plant can use directly to make amino acids and thus proteins. Legumes have long been an essential alternative to protein-rich but more costly animal foods, and are especially prominent in the foods of Asia, Central and South America, and the Mediterranean. A remarkable sign of their status in the ancient world is the fact that each of the four major legumes known to Rome lent its name to a prominent Roman family: Fabius comes from the fava bean, Lentulus from the lentil, Piso from the pea, and Cicero— most distinguished of them all—from the chick pea. No other food group has been so honored!