This large grassland species is well sought after for eating. There is a similar species, A. crocodilinus, that is claimed to be often mistaken for A. arvensis, but a bit of research shows they can be easily told apart, even if you don't have a microscope. Spores for A. arvensis are 9–11 x 5–6.5 µm, ellipsoid, while those for A. crocodilinus are much smaller at 6-9 x 4-6 µm.
Common name: Horse Mushroom
Substrate: Lawn or Pasture
Height: 150 mm
Width: 150 mm
On occasion, I come across what looks like A. arvensis that I find inside the bush line, and I wonder if these are not A. crocodilinus. The short, stumpy size and small scales around the lower stem make me think it could be. Unfortunately, I have not had the chance to see a mature species or to look at these with a microscope.