There are five distinct types of lettuce: leaf (also called loose-leaf lettuce), Cos or romaine, crisphead, butterhead and stem (also called asparagus lettuce). Leaf lettuce, the most widely adapted type, produces crisp leaves loosely arranged on the stalk. Nearly every garden has at least a short row of leaf lettuce, making it the most widely planted salad vegetable. Cos or romaine forms an upright, elongated head and is an excellent addition to salads and sandwiches. The butterhead varieties are generally small, loose-heading types that have tender, soft leaves with a delicate sweet flavor. Stem lettuce forms an enlarged seedstalk that is used mainly in stewed, creamed and Chinese dishes. Crisphead varieties, the iceberg types common at supermarkets all over the country, are adapted to northern conditions and require the most care. In areas without long, cool seasons, they generally are grown from transplants, started early and moved to the garden as soon as the soil can be worked. They are extremely sensitive to heat and must mature before the first hot spell of summer to achieve high-quality heads. If an unseasonably early heat wave hits before they have matured, they almost certainly fail. In many locations, crisphead lettuce plants started in late summer to mature in the cooler weather of fall have a much better chance of success.