 The Romans referred to lettuce as lactuca ( lac meaning milk in Latin ) , an allusion to the white substance , now called latex , exuded by cut stems . This word has become the genus name , while sativa ( meaning " sown " or " cultivated " ) was added to create the species name . The current word lettuce , originally from Middle English , came from the Old French <unk> or <unk> , which derived from the Roman name . The name romaine came from that type 's use in the Roman papal gardens , while cos , another term for romaine lettuce , came from the earliest European seeds of the type from the Greek island of Cos , a center of lettuce farming in the Byzantine period . 
