A small Psathyrella associated with Reedmace, Common Reed, etc..  Pale brown cap, conical at first, flattening later.  It is striate with small flecks of creamy-brown veil.   Gills pinkish to dark brown, stem white.  

Other Psathyella are similar, but the habitat assists identification

habitat

Photograph from top down, in side view and from underneath to show gills and full length of stipe.  You must note habitat and substrate and it is helpful to have a field photo.

on stems of Reedmace (Typha), Common Reed (Phragmites) just above water-line

Widespread but uncommon (Kibby Vol.3, 2021)

Rare in Leicestershire and Rutland.