These are dried shiitake mushrooms and can be black, light brown, or speckled. They have thick caps, curled edges, and a meaty flavor. Although shiitake mushrooms are also available fresh and can be substituted, dried mushrooms are sometimes preferred because the drying process intensifies their flavor. Soak them in warm water for 20 minutes to rehydrate them before cooking. According to traditional Chinese medicine, these mushrooms boost the immune system and act as an aphrodisiac.