Inonotus tomentosus

This is a key to gilled mushrooms, that is, mushrooms having a definite cap with a fertile surface consisting of gills. The fruiting body usually also has a stem, although that may be lateral or absent (usually, then, the mushroom is growing from wood). You can use this key to identify mushrooms that you find.

Fertile surface usually a layer of vertical tubes, of which the mouths are visible as pores on the underside of the cap or shelf.
Fruiting bodies usually tougher or harder than the "normal" gilled mushrooms, being leathery, corky, or woody. But they can be quite tender while actively growing
Once grown, they do not decay easily, remaining on the substrate for months or years
They often grow on wood, although a few are terrestrial (even those are usually growing on buried wood)
Fruiting body is usually a flat shelf, or hoof-shaped, protruding directly from the substrate, although sometimes it may have a short stalk.
Some forms never grow away from the substrate at all, so that all that is visible of the fruiting body are the pores.
Sometimes the pores are so minute that the fertile surface seems solid, until you look closely

Growing on wood

Not fitting the other choices, not stipitate
In making choices below based on texture and size, place the emphasis on texture: if left alone, some of the smaller ones can eventually get quite big; and even the huge ones have to start out small at first

Fruiting body medium-sized, soft; shelving, often hairy or velvety when young, becoming smooth in age, often imbricate or compound
Brownish or bright yellow cap surface with (when young) whitish pores
Usually exuding liquid when squeezed or cut; often beaded with droplets on its own

Fruiting body hairy, usually brownish
Flesh yellowish- to reddish-brown, changing quickly to dark brown or black with KOH

Spore deposit white, fruiting body various shades of brown
Most common pileate species here

Inonotus Mega Setae     Section Setae projecting more than 50 µm into tubes All stipitate, terrestrial species go here, although some of these also occur sessile on wood

Links from Look-alikes Shortoporus     Subtribe Cap and stipe fleshy and substantial, flexible Pores very short: 1-5 mm Pore surface pale Fruiting bodies irregular, often slightly lobed, stalk often off-center Fruiting bodies sometimes clustered or compound, but more often singly or in troops

Inonotus tomentosus     (Fries) Teng