Somewhat confusing species to identify. Bucsacki describes it as "highly variable",and even the literature doesn't seem to agree with itself. The gills are described as "slightly decurrent" in some sources, whilst other state they are either adnexed or slightly decurrent. Had me confused for a while! (in this specimen they are adnexed).
I think the real clue are the "roots" at the base of the stem which went down a good 5cm under the ground.
These were growing (amongst the nettles - I have the stings to prove it!) in a small clump on what appeared to be a piece of buried branch.
Not rare, but only the second agaric I have found in my wood this year.