Looseleaf lettuce seeds produce heads that are simply constructed like rosettes, with a spiral of leaves growing around a tender center. Looseleaf lettuces do not form any kind of stem to speak of until they go to seed, sending up a tall flower stalk from the central growing point. Loose leaf lettuce is probably the simplest lettuce to grow and harvest. Pick leaves from the outer edges of the plants, or harvest whole plants all at once. It is nice to grow several different loosleaf lettuce varieties because they come in a wide range of colours and shapes.