Reishi mushrooms, also known as Ganoderma lucidum, are a type of fungus that has been used in traditional medicine for centuries, particularly in Chinese medicine. They are often referred to as the "mushroom of immortality" due to their potential health benefits. These mushrooms are typically found growing on decaying wood and have a glossy, reddish-brown appearance. Reishi mushrooms are believed to support the immune system, reduce stress, and improve sleep quality, making them popular in dietary supplements and herbal remedies.