Butter lettuce in field Photo Credit bangkokhappiness/iStock/Getty Images. Butter lettuce is a variety of butterhead lettuce, known for its smooth, loosely bunched, tender leaves.Because of its delicacy, this heading lettuce is often kept in plastic clamshell containers in grocery stores to protect it from accidental bruising.utter lettuce in field Photo Credit bangkokhappiness/iStock/Getty Images. Butter lettuce is a variety of butterhead lettuce, known for its smooth, loosely bunched, tender leaves.