Chaga (Inonotus obliquus) is a parasitic medicinal fungus most commonly found growing on birch trees throughout the cold forests of the Northern Hemisphere. Rather than forming a typical mushroom cap, it develops as a large, irregular black mass that protrudes from the bark of infected trees. This hardened outer layer looks like charred wood, while the interior is a softer golden-brown corky tissue.

The fungus grows slowly, sometimes taking many years to form large conks. It typically infects birch species through wounds in the bark and gradually feeds on the tree over decades. Eventually the fungus produces reproductive structures inside the dying host tree, completing its life cycle.

Chaga is most abundant in northern forests across Siberia, Scandinavia, northern Europe, Canada, and parts of the northern United States. It prefers mature birch stands in cool climates and shaded forest environments.

Historically valued as both a medicinal fungus and a survival beverage, chaga has been prepared as a dark, earthy tea for centuries. Its high concentration of antioxidant compounds and immune-supportive polysaccharides has made it one of the most widely recognized medicinal fungi in modern herbal medicine.