Agrocybe sp.

The fruit bodies are mushrooms with caps atop central stems. The caps range from a few to 20 centimetres in diameter and are broadly conical to fairly flat in shape (but then often with a slight central bump). Usually the caps are predominantly some shade of brown, but they may be whitish towards the margin and in some species the caps are very pale overall.

The gills are pale at fist but become brown with age, as the spores mature.

There is a partial veil over the gills in immature mushrooms and after the cap has expanded a veil remnant may remain as a ring of tissue around the stem. However, this ring may be fairly flimsy and hard to see (or even absent) in aged specimens. 

 Spore print: brown.

Mostly they appear on the ground but at least one species in the local area grows on live trees. Most common in Canberra are members of the Agrocybe praecox group (http://canberra.naturemapr.org/Community/Species/21570) which often appear in spring to summer on woodchip mulch.