Chaga is a mushroom or fungi typically found in very cold regions like Siberia. The Chaga mushroom has been used for holistic treatments in the Far East for many centuries. Topical solutions have been known to aid in skin ailments and the tea derived from the fungi has a myriad of uses from easing stomach distress to building the immune system to fighting cancer.
The only version of the Chaga that may be consumed is that grown on a Birch tree. Chaga can be found in other areas, but is not as safe for human consumption and does not seem to have the same positive effects of the Birch Chaga. Unique in that it is a polypore instead of a gilled fungus, Chaga appears black and irregular; almost like a cracked mass on the trunk of the Birch tree. You might pass it without realizing it is a mushroom.
It is believed the Chaga develops its rich antioxidant qualities as well as the anti-cancer betulinic acid by leaching it from the birch bark. The process the mushroom uses to grow makes the acid usable by humans. Typically betulinic acid is not something safe for oral consumption, but in this form it is and actively fights against cancer.