Romaine or cos lettuce (Lactuca sativa L. var. longifolia) is a variety of lettuce that grows in a tall head of sturdy dark green leaves with firm ribs down their centers. ... In North America, romaine is sold as whole heads or as “hearts” that have had the outer leaves removed and are often packaged together.
Storage Tips for Romaine Lettuce
They will keep for 2 to 3 days. Store Romaine lettuce unwashed in a loosely closed plastic bag in the refrigerator, or wash the leaves, dry them thoroughly, and refrigerate in a tightly sealed plastic bag. Either way, Romaine should last for up to a week.