Marasmius oreades is known the world over as the fairy ring mushroom. I have not come upon them in the wild, though they do grow in Australia, having probably been imported from Europe. I came upon them in a market in Perth, where they were being sold for $160 per kilogram, imported from France! The picture below shows what they look like by the time they have been picked, shipped and packed. In France, these are known as Mousserons. Note. October 2012. After investigating further during my trip to France, it appears that Marasmius oreades is known as the Faux Mousseron. Mousseron is applied to Marasmius oreades by English speakers, while the French refer to Calocybe gambosa or St George’s mushroom as mousseron, or mousseron vrai. This muddies the waters somewhat as it is not easy to distinguish the identity of the dried specimens above. The way the stems split and their relative thickness would seem to be contrary to what one would expect from M. oreades. I will pick some in the morning and investigate this further. I will leave the reader to investigate further the identification of these mushrooms. This investigation should be undertaken with care, as there are lots of mushrooms that come up in fairy rings, and some of them are extremely poisonous. Here is a link describing them in Victoria. (I need to find a new link it seems) Update October 2012 Here is a picture of some of these mushrooms growing in France, in the village of Correze, which I am visiting to attend the annual mushroom festival. These are in the lawn of the place where I am staying. I will take one down to the fete tomorrow to have the identification verified.
A couple of distinctive features of this mushroom are the dark raised central region of the cap, and the toughness of the stem, which can be twisted back on itself without breaking.
While I was in France, I was invited to visit a farm in the Alpes Maritimes, at an elevation of 1000m. Here I was shown M. oreades growing in classic fairy rings in an open paddock. The rings could be seen quite clearly by their dark green colour in comparison to the surrounding grass. The image below shows my host kneeling down to harvest some mushrooms from one of the rings.