Inonotus obliquus


Inonotus obliquus, commonly known as chaga, is a fungus in the family Hymenochaetaceae. It is parasitic on birch and other trees. The sterile conk is irregularly formed and has the appearance of burnt charcoal. It is not the fruiting body of the fungus, but a sclerotium or mass of mycelium, mostly black because of the presence of massive amounts of melanin. Some people consider chaga to be medicinal.
I. obliquus is found most commonly in the Circumboreal Region of the Northern Hemisphere, where it is distributed in birch forests.

Morphology

I. obliquus causes a white heart rot to develop in the host tree. The chaga spores enter the tree through wounds, particularly poorly healed branch stubs. The white rot decay will spread throughout the heartwood of the host. During the infection cycle, penetration of the sapwood occurs only around the sterile exterior mycelium mass. The chaga fungus will continue to cause decay within the living tree for 10–80+ years. While the tree is alive, only sterile mycelial masses are produced. The sexual stage begins after the tree, or some portion of the tree, is killed by the infection. I. obliquus will begin to produce fertile fruiting bodies underneath the bark. These bodies begin as a whitish mass that turn to brown with time. Since the sexual stage occurs almost entirely under the bark, the fruiting body is rarely seen. These fruiting bodies produce basidiospores which will spread the infection to other vulnerable trees.

Common names

The name chaga comes from the Russian name of the fungus, which in turn is purportedly derived from the word for the fungus in Komi-Permyak, the language of the indigenous peoples in the Kama River Basin, west of the Ural Mountains. It is also known as the clinker polypore, cinder conk, black mass and birch canker polypore. In England and officially in Canada, it is known as the sterile conk trunk rot of birch.

Distribution and cultivation

Generally found growing on birch trees, it has also been found on alder, beech, oak and poplar. In species other than birch, the fungus often appears as buried stem canker, instead of the charcoal-like mass found on birch trees.
Attempts at cultivating this fungus on potato dextrose agar and other simulated mediums resulted in a reduced and markedly different production of metabolites. Cultivated chaga developed a reduced number of phytosterols, particularly lanosterol, an intermediate in the synthesis of ergosterol and lanostane-type triterpenes.

Chemistry

The black sclerotium has been shown to contain large concentrations of melanin. Chaga has been reported to contain extremely high concentrations of oxalate, 2800–11200 mg total oxalates/100 g sclerotium, one of the highest reported levels of any organism.

Preparation

Chaga is traditionally grated into a fine powder and used to brew a beverage resembling coffee or tea. However, caution is warranted with chronic use due to the extremely high concentrations of oxalates in chaga. Currently, three extraction processes are used.