There are hundreds of different lettuces, but they can be divided into four main categories. Loose-leaf types such as oakleaf and bitter lollo rosso do not form a distinct heart or head and are sometimes referred to as cut-and-come-again lettuces, meaning the gardener can harvest some of the leaves without uprooting the whole plant.
Cos or romaine lettuces have elongated bright green leaves and a nutty flavour; Little Gem are a baby version of cos. Butterhead lettuces have small loose heads and soft, mid-green leaves, while crisphead varieties such as iceberg and Webb's Wonder have tightly packed heads of crisp leaves. In general, the darker varieties are the most nutritious, having the highest concentrations of vitamins A and C, plus folate and calcium.
Lettuces need to be washed thoroughly, however loose leafed varieties should not be left to soak because this can make them limp. Dry them thoroughly in a salad spinner - remember leaves need to be very dry so that salad dressing can cling to them. Bagged salads have their place, but the fresher a lettuce is, the better it will taste and the higher its nutritional content will be. Tear salad leaves rather than cut them - blunt lives will bruise the leaves and break down the cellular structure. Alternatively, consider serving tightly packed lettuces in wedges so you can appreciate the crunch of the layers as you bite into them.