From my experience, Arrhenia retiruga is very tiny, difficult to come across, and hard to find in fungi encylopedic books! It is classed as a member of the Tricholomataceae, according to Roger Phillips.
My first sighting of Arrhenia retiruga was over a year ago at University Park. The Nottingham University Park consists of 300 acres of grounds and has been part of the University of Nottingham since 1929. There is a huge swathe of meadow land which is allowed to grow wild and it is there I first spotted Arrhenia. Conditions were damp and moist and amongst a heavily mossy patch in the grass was a small group. I was a little baffled as there was no stem, no gills and the cap just seemed to rest somehow amongst the grass and moss, but somehow seemed firmly attached. I took photographs but archived them until I spotted the same again this year in exactly the same area. I took more photographs (and they are incredibly difficult to photograph) as the cap is very pale in colour being whitish, grey and pallid and being tiny 0.5 cm or so, and seemingly buried in the moss. While researching some other fungi I did come across a photograph and was able to identify.
This fungus is uncommon. The characteristics are as follows:
0.5-1.5cm. Disc, cupped shaped or fan shaped. Lobed margin. White/greyish, delicate.
No stem or gills. Habitat usually moss, but can be seen on dead grass and twigs. Winter to Spring.
It reminded me of a tiny mother of pearl in moss!
This can now be seen on Browse 4 on fungiworld.co.uk