Marasmius rotula

Common Name: None.
Description: Cap 1.5-17 mm across, hemispherical, then convex with a central depression with deep radial grooves; pale yellowish brown, yellow to pallid; dry and minutely granular. Stem 15-85 by 1 mm high and wide.
Habitat: gregarious or in clusters on wood of deciduous trees or on leaf litter. Found widely distributed in much of North America, but commoner in the East.
Edible: No.

Source: Mushrooms of North America by Roger Phillips.