Inonotus obliquus (Fr.) Pilat Birch Conk, Chaga, Clinker Polypore, Fruit body sterile conk 25-40cm across; black; deeply cracked, very hard and brittle when dry. Fertile portion 5m thick, crust-like, thin; dark brown. Tubes 3-l0mm deep, brittle, usually split in front. Pores 6-8 per mm, circular; whitish becoming dark brown. No stem. Flesh corky, faintly zoned; bright yellowish brown. Spores broadly ellipsoid to ovoid, smooth, 9-10 x 5.5-6.5µ. Setae present. Habitat beneath the bark or outer layers of wood on living, dead, standing, or fallen trees, erupting into conspicuous black conks, generally on birch, elm, and alder. Found in northern North America, and northern Europe to Russia. Season all year. Not edible although it comes highly recomended for cancer treatments, it is this fungus that is discussed by Solzhinitsyn in his book 'The Cancer Ward', a tea made from the fungus is drunk daily, the fungus has been found to contain inotodiol which has active anti-tumor properties. (It is only the specimens growing on Birch trees that seem to have this property). It has also been shown to have antiviral activity against HIV.