 Lettuce is most often used for salads , although it is also seen in other kinds of food , such as soups , sandwiches and wraps ; it can also be grilled . One variety , the <unk> ( <unk> ) , or asparagus lettuce , is grown for its stems , which are eaten either raw or cooked . Lettuce is a rich source of vitamin K and vitamin A , and is a moderate source of folate and iron . Contaminated lettuce is often a source of bacterial , viral and parasitic outbreaks in humans , including E. coli and Salmonella . In addition to its main use as a leafy green , it has also gathered religious and medicinal significance over centuries of human consumption . 
