There are at least 18 types of lettuce. Below you will find a list with a brief description. Please refer to this page at epicurious for Alternate Names, full characteristics and how to use them.
Arugula: this green tastes earthy and slightly tart with a bold, peppery kick.
Baby Beet Greens: slightly spicy
Butterhead Lettuce: the texture of a butter lettuce is indeed smooth like butter.
Coral Lettuce: The sturdy, crisp leaves have tight, frilly curls and a mild flavor.
Cress: mature watercress has a tough, fibrous stem and small green leaves (the stems of baby watercress are generally more tender).
Endive: unique oval shape, soft, satiny texture, and slight bitterness.
Escarole: this mildly bitter leafy green
Frisee: slightly bitter in taste
Iceberg Lettuce: very crisp, watery, and refreshing
Little Gem: leaves are crisp, sweet, and sturdy
Looseleaf Lettuce: mild flavor and are very pliable
Mache: mild and slightly sweet flavor
Mesclun: not a specific type of lettuce, but rather a loose mix of tender baby lettuce leaves.
Mizuna: strong, spicy flavor
Oakleaf Lettuce: delicate and tender
Radicchio: for lovers of bitter lettuce
Romaine: center rib gives it a real crunch. The rib also gives this lettuce a slight bitter .
Sorrel: tart and quite lemony.
Speckled Lettuce: Many varieties, the specks give it their name.
Stem Lettuce: eaves can be bitter, like escarole, but the stalk, which should be peeled, has a nutty, cucumber-like flavor.
Tatsoi: mild, mustardlike flavor.