Lentinus tigrinus

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.

Fruiting body containing fibers (usually in the stalk)

Spore print "light-colored": white or buff, sometimes tinged with pink or tan. Greenish and (except for the Russulales) yellow spore prints also go here
Stalk fibrous, not fracturing like a piece of chalk

None of the special features distinguishing the other white-spored genera:
Gills not free, as in the Lepiotas and Amanitas
Basidia not extra-long, as in the Hygrophoraceae
Spores smooth, except for Lentinellus

Growing on trees or dead wood, leaves, or sticks, or organic debris, often in moss

All mushrooms with serrated gills go here
If the stem is central and well-developed, then the fruiting body (even the cap) is large and extremely tough

Cap usually scaly, often quite large
Fruiting body tough to extremely tough
Stalk central, well-developed
Spores inamyloid, smooth, elliptical

Lentinus tigrinus     (Fries) Fries