Romaine or cos lettuce is a variety of lettuce that grows in a tall head of sturdy dark green leaves with firm ribs down their centers. Unlike most lettuces, it is tolerant of heat. In North America, romaine is sold as whole heads or as “hearts” that have had the outer leaves removed and are often packaged together. What are the benefits of romaine lettuce?Although it’s low in fiber, it’s high in minerals, such as calcium, phosphorous, magnesium, and potassium. It’s naturally low in sodium. Plus, romaine lettuce is packed with vitamin C, vitamin K, and folate. It’s a good source of beta carotene, which converts into vitamin A in the body.