Pileus: plano-convex to deeply funnel-shaped.
Stipe: fleshy fibrous (cartilaginous in a few species)
Stature: Clitocyboid or Naucorioid
Ecology: saprophytic on the ground, humus or decayed wood. Often more abundant in the late summer or fall.
Basidiospores: smooth, white, always inamyloid
Spore Print: white to cream, or greenish to pale salmon
Lamellae: Usually white, close, adnate to decurrent
Lamellar Trama: regular (except bilateral in the primordium)
Pileipellis: a cutis
This, in my experience, is often not an easy genus to identify in the field. The easy ones have a depressed, somewhat funnel-like cap shape, and are often white or off-white in color. The more difficult ones have adnate rather than decurrent gills. Fries included all white spored mushrooms without veils or volva and decurrent to subdecurrent gills in Clitocybe.
Over the years agricologists have separated the original Friesian concept into a number of separate genera. Singer, 1986 recognized 12 genera. Largent lists 16 modern genera. The ones included in the first edition of this work are Armillariella, Hygrophorus, Laccaria, Lepista, Omphalotus, Pleurotus and Tricholomopsis. So, in the Friesian sense these all belonged to Clitocybe.
Arora, 1986 suggests using a process of elimination to identify this genus:
Not soft and waxy gills as in Hygrophoraceae
Not orange like Hygrophoropsis or Omphalotus
Not brittle like Russula
No latex like Lactarius
No notched gills like Tricholoma
Fleshy stalk is unlike Gymnopus (Collybia) cartilaginous stalk (a few species do have the cartilaginous stalk (Largent and Thiers, 1977).
Largent and Thiers, 1977 in the same vein add:
No colored lamellae like Laccaria
No repeatedly forked lamellae like Hygrophoropsis
No pinkish hymenophore like Lepista
Singer, 1986 adds to the discussion, that Lepista's roughened or warty cyanophilous spores help differentiate it from the always smooth spores of Clitocybe. Others still include Lepista in Clitocybe. This is a good lesson to the student, that no matter what information and "proof" is presented, systematics still is a matter of personal opinion, and the mushroom doesn't care what its name is.
There are probably over 200 species in North America.