Shiitake mushrooms, widely used in Asian cooking, command a higher per pound price than ordinary white button mushrooms, but they're distincly flavored; even a small quantity adds flavor impact. Shiitakes are available in the produce section of larger supermarkets as well as in specialty markets and Asian groceries.
The shiitake has a flat, broad brown cap and paler stem. Stems are flavorful but tough; remove them before cooking. Save the stems to flavor soup stock if the broth will be strained before serving.