Clitocybe robusta

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 the ground

Found in woods
Not rooting

Gills attached to decurrent
Coloration usually white to greyish brown, sometimes purple or with purple tones
Never with a ring of any kind

Gills attached to decurrent, crowded
Cap glabrous, small to very large; often aging into a funnel shape
Spore print often tinged with pink or buff
Look for things here if they have non-free gills and don't fit the other taxa

White Clitocybe     Section Fruiting body entirely white

Links from Look-alikes Blewit     Section Spore print pinkish buff Fruiting body often with some purple coloration, although this tends to be less, the larger the fruiting body is Cap smooth, margin wavy, usually inrolled even after the cap has fully expanded Flesh hygrophanous (usually all the way through the cap), often with a slightly soapy look and feel to it (wet your finger first to get the full effect)

Clitocybe robusta     Peck