Inonotus obliquus is best known as chaga mushroom. (Although it is a sclerotia [1] and not a mushroom)
Chaga is well known for its anti tumor,antiviral, and anti-inflammatory properties. Its also a high source of melanin and one of the highest sources of antioxidants found in nature.
It grows on a few species of trees but it's primary hosts is Betula papyrifer or (white birch). The medicinal chaga is only harvested from birch trees due to chaga's ability to convert the Betulinic Acid[2] into a bioavailable form giving it powerful medicinal qualities. A great discovery in the fight against cancer.
What's commonly known as chaga. The black sclerotia takes 5yrs or longer before it's big enough to be harvested.
This is fruiting stage that is rarely seen. So rare that a few mycologists have spent their whole career looking for one and never finding it.
It can take years after the host tree dies for a chaga to fruit. A resupinate layer forms under the barking building up pressure until the bark explodes open allowing the surface full of tubes to release their spores.
I first learned about this from an article
and during the mid summer into fall of 2016 I found 13 fruiting chaga's. A very lucky year as I haven't found one since.
http://www.fungimag.com/fall-2012-articles/V5I3SignificantOtherLR.pdf
It often takes atleast 20yrs from the host trees initial infection to the end stage of fruiting.
Close up of the pore surface. It has millions of tubes full of spores. Not much is known how it spreads, it could use the wind or the spores could be carried by insects who quickly consume this for its nutritional value.