This section is from the book "Studies of American Fungi: Mushrooms, Edible, Poisonous, Etc.", by George Francis Atkinson. Also available from Amazon: Studies of American Fungi: Mushrooms, Edible, Poisonous, Etc..
Polyporus fomentarius (L.) Fr. [Fomes fomentarius (L.) Fr.,] is hoof-shaped, smoky in color, or gray, and of various shades of dull brown. It is strongly zoned and sulcate, marking off each year's growth. The margin is thick and blunt, and the tube surface concave, the tubes having quite large mouths so that they can be readily seen, the color when mature being reddish brown. Sections of the plant show that the tubes are very long, the different years' growth not being marked off so distinctly as in P. applanatus and leucophaeus. The plant grows on birch, beech, maple, etc. The inner portion was once used as tinder.
Polyporus pinicola (Swartz.) Fr.[Famespinicola (Swartz.) Fr.Joccurs on dead pine, spruce, balsam, hemlock spruce, and other conifers. The cap is about the width of the F. applanatus, but it is stouter, and does not have the same hard crust. The young growth at the margin, which is very thick, is whitish yellow, while the old zones are reddish. The tubes are yellowish, and sections show that they are in strata corresponding to the years' growth. Polyporus igniarius (L.) Fr. [Forties igniarius (L.) Fr.J is a black species, more or less triangular, or sometimes hoof-shaped. The yearly zones are smaller, become much cracked, and the tubes are dark brown. One of these plants which 1 found on a birch tree in the Adirondacks was over 80 years old.