Many species of lichens are found around the world. It is estimated that at least 20,000 different species exist, and more are found every year. And yes, some lichens are edible—but like hunting for wild, edible mushrooms, you really have to be an expert, as some lichens contain toxic acids. Historically, for example, the Black Tree lichen (Alectoria) was used by Montana Indians who would wash and soak the lichens, then cook them for one to two days in a steam pit. It was eaten or dried and powdered, then used as a mush or thickener later. (The Flathead Indian families reportedly ate 25 pounds [11.34 kilograms] of lichens each year.) Another edible lichen is the Reindeer moss (Cetraria)—often used in Switzerland for its benefits to the digestive system—and added to meats and pastries to retard spoilage. In fact, a lichen called Old Man’s Beard (Usnea), once used for dye, is thought to contain antibiotic substances, and also used as an antimicrobial compress and dressing for open wounds. And Iceland moss (Cetraria islandica), found in the mountains of northern regions, is considered nutritious—but it was used mainly in earlier times for soups, stews, and even in breads.