The foundation of most salads is a leafy green, usually lettuce. A member of the daisy family, lettuce is thought to have come from Central Asia and was cultivated in the royal gardens of Persia around 500 BC. Four main types of lettuce exist today: looseleaf, cos (romaine), butterhead, and crisphead (Iceberg). Looseleaf varieties include black-seeded Simpson, Oakleaf, Salad Bowl, and the red varieties (Red Sails and Red Salad Bowl). Butterhead lettuces, Bibb and Boston, are most prized by chefs for their tender, sweet leaves. Romaine lettuce is crisper than looseleaf and has a longer shelf life. Escarole, a peppery green, is highly prized for its peppery taste and its spiky look.