Psathyrella spadicea  (Schaeff.) Singer (1951)

This is  rather large Psathyrella that reminds one of Agrocybe in the field. It's typical habit is caespitose at the base of dead or dying trees. Identification is greatly enhanced by the distinctive microscopical structures.

Cystidiogram -- thick walled, metuloid like cystidia, some with apical crystals