A number of similar polypores, and even a few species of crust fungi, look more or less identical to the casual eye, and a whole host of mushrooms are thus lumped together as "turkey tails" by collectors who are more interested in gilled mushrooms and boletes. But if you are one of those folks, like me, who just has to be sure, I offer the Totally True Turkey Tail Test, below.
Totally True Turkey Tail Test
1) Is the pore surface a real pore surface? Like, can you see actual pores?
No: See Stereum ostrea and other crust fungi.
2) Squint real hard. Would you say there are about 1–3 pores per millimeter (which would make them fairly easy to see), or about 3–8 pores per millimeter (which would make them very tiny)?
3–8 per mm: Continue.
1–3 per mm: See several other species of Trametes.
3) Is the cap conspicuously fuzzy, velvety, or finely hairy (use a magnifying glass or rub it with your thumb)?
No: See several other species of Trametes.
4) Is the fresh cap whitish to grayish?
Yes: See Trametes hirsuta.
5) Does the cap lack starkly contrasting color zones (are the zones merely textural, or do they represent subtle shades of the same color)?
Yes: See Trametes pubescens.
6) Is the fresh mushroom rigid and hard, or thin and flexible?
Rigid and hard: See Trametes ochracea.
Thin and flexible: Totally True Turkey Tail.