Summary:
Inonotus obliquus forms large black stemless cracked cankers on birch. Fruitbodies on the other hand are quickly deteriorated by insects and weathering and are hard to find even where infected trees are numerous. The pore surface is whitish becoming dark reddish brown. Microscopically, there are scattered setae that do not project prominently. Claims are made for its use as a medicinal agent.

Odor:
indistinct (Buczacki)

Taste:
indistinct (Buczacki)

Microscopic:
spores 9-10 x 5.5-6.5 microns, broadly elliptic to oval, inamyloid, colorless to pale brownish, illustrated as smooth; basidia 4-spored, 15-18 x 11-12 microns, broadly clavate; setae scattered, scarcely projecting or imbedded, 16-22 x 4.5-7 microns, subulate to ventricose; context hyphae 3.5-7 microns wide, "dark brown in KOH solution, thin- to moderately thick-walled, with frequent branching, simple-septate", trama hyphae "not easily separable, apparently similar", 2.5-3.5 microns wide, (Gilbertson), spores 7-10 x 3.5-5.5 microns, (Breitenbach)

Spore Deposit:
white (Buczacki)

Notes:
Inonotus obliquus has been found in BC, ID, AB, MB, NB, NS, NWT, ON, PE, PQ, SK, AR, GA, MA, ME, MT, NH, NY, PA, VT, and WV, and it is circumglobal in boreal forest ecosystems with birches, (Gilbertson). It has also been found in YT (Ginns). It also occurs in Europe and Asia, (Breitenbach).

Synonyms and Alternate Names:
Polyporus obliquus Pers.: Fr.
Poria obliqua (Pers.: Fr.) Quel.