Since water-filtering oysters readily take on the flavor of their environment, they traditionally are named after the area where they grow. In general, colder waters develop a firmer texture and sharper, saltier flavor, while warmer waters create a milder, softer oyster.
These oysters tend to have a bumpy, elongated shell and a briny flavor with strong mineral notes. Varieties include Blue Point, Cape Cod, Chesapeake, Kent Island, Long Island, Malpeque and Wellfleet. Atlantic oysters, also called Eastern oysters, account for most of the oysters sold at market.
Also known as Japanese oysters, these specimens have more subtle, slightly fruity flavors and more distinctly fluted shells than their Atlantic cousins. Popular varieties are the Hama Hama, Hog Island, Quilcene and Tomales Bay. The sweet, popular Kumamoto oyster is actually a separate species, but it is often grouped with the Pacific oysters.
A species indigenous to the American Northwest, Olympia oysters are tiny (about the size of a quarter), slow growing (taking 4 years to mature) and highly prized for their flavor. They are almost always served on the half shell.
Flat oysters are native to European waters but now are grown in both the Atlantic and Pacific. Varieties found in the waters off Maine and Northern California have especially intense flavors. Small oysters inside large, round shells, they are commonly known by the name Belon, after a French region where they were once abundant.
Adapted from Williams-Sonoma Kitchen Companion: The A to Z Guide to Everyday Cooking, Equipment and Ingredients (Time-Life Books, 2000)