Common name: Chaga, Clinker Fungus.
Description and identifying characteristics: A black, deeply-cracked conk growing on birch. It has a burn-charcoal appearance with a deeply cracked/warty texture on the outside, and a yellow to yellow-brown interior, sometimes with small dots or swishes of white intertwined in the matrix of the mushroom. It can sometimes be brittle, with pieces of the mushroom easily falling off.
Ecology/associated host or habitat: A parasite found growing on yellow or white birch (Betula) trees. It grows perennially, and can be found year-round.
Poisonous look-alikes: There are no poisonous look-alikes to this fungus. There are other non-chaga cankers that grow on other species of tree, so do not harvest chaga from any species but birch (Betula species).
Methods and Tips on harvesting: Chaga is a perennial growth, so it can be harvested year-round. This is the only mushroom you will likely need to use an ax or hatchet to harvest! A hammer can be useful as well.
When harvesting chaga, do not cut into the sapwood, let alone heartwood, of the tree. If you harvest the mushroom properly, you can harvest the same tree again in 4 years (see reference from Fiddlehead Heaven below). If you penetrate the wood of the tree, you will kill the tree and it will not produce any further chaga.
Do not harvest chaga from a dead tree. The mushroom will have no medicinal value, and the tea made from the mushroom will be bitter.
Possible allergic reactions and symptoms: There are no documented allergic reactions to this fungus
Special considerations for storage. As with other mushrooms, the storage of mushrooms is best in containers that allow some gas exchange rather than containers do not. In other words, mushrooms are better stored in paper bags than plastic ones. Do not store this or any other mushroom in an airtight, Ziploc-type bag.
Photos:
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Chaga growing on Birch (Betula) trees
Showing fertile layer
References:
Fiddlehead Heaven’s tips for harvesting chaga
More information from Fiddlehead Heaven on their chaga research
An example of how not to harvest chaga (but useful information)