Chaga is a mushroom (Inonotus obliquus) that grows on the bark of birch trees in cold climates like Northern Canada, Alaska, Siberia, and Scandinavia. It appears as a large, woody growth 25 to 38 centimeters across. Rich in antioxidants, Chaga may support immune health, reduce cholesterol, and even help fight cancer. It’s commonly consumed as tea or a supplement.