What we commonly call the field mushroom or Agaricus Campestris is probably a little more complicated then we would like. In a nut shell these mushrooms are more likely a species cluster, some named others not. Having said that with a little bit of knowledge and a few ID tricks its not to hard to stay safe while picking and eating field mushrooms. Found growing in paddocks, fields, parks and lawns over summer and into autumn these are a common mushroom that tastes ok, is easy to ID and is socially exceptable! Unless of course you don’t ask permission to harvest on private property!
The cap is predominately white, dry and smooth, sometimes with fine brown scales or cracks. The gills start pale pink then become light then chocolate brown as they mature. They do not attach to the stem. There is a white vale present that soon brakes leaving in some cases a slight ring and sometimes some fragments on the edge of the cap. The spore print is always chocolate brown. The stem is short and tapers at the base, never bulbous or forming from a volva sack. The stem will brake cleanly from the cap. the flesh is white sometimes staining lightly pink, never yellow. the odor is pleasant, mushroomy, similar to store bought button mushrooms. They grow from the ground amongst grass and not from a cow pat.
The above description is of a white field mushroom, the agaricus family is much bigger then this and many of them are edible, some are poisonous. The Agaricus Xanthodermus section covers most of the poisonous species. They are known as the yellow stainers, the base of the stem is a good place to check, break and crush the end of the stem and watch for any colour change. At the same time smell the crushed section. Yellow staining and an unpleasant odor means that its probably a poisonous agaricus and not edible.
Below is a typical agaricus xanthodermus, the stem is long, there is an obvious ring, the base of the stem stains yellow, the odor is unpleasant, the gills are white then become a very light pink, brown much later. The cap is white and somewhat ‘boxy’. I found these growing in a dense cluster.
Agaricus Xantodermus AKA the yellow strainer, poisonous.
Below is another common yellow stainer, again the gills start white and become pink, only turning brown much latter, long stem, yellow staining, unpleasant odor. These have a grey cap with dark grey to black scales. These were also growing in a dense cluster, more likely on a roadside or forest.
poisonous agaricus similar to A. Moelleri
Besides the yellow stainers there are a range of small white mushrooms that can be mistaken for field mushrooms. Here is an example of an Amanita species that could be confused with agaricus. If there are any ID discrepancies with your find its best to do a spore print over night. By that time the gills will change colour and the spore colour will confirm if its an agricus sp. a black or white spore print is a warning that the mushroom in question is not an agaricus and should not be eaten unless an ID can be made. Never eat a mushroom that has not been ‘100%’ identified. An easy way to get a second opinion is to take clear close up photos of the cap, gills and stem and post it on one of the good mushroom ID pages on Facebook along with a description of the area where it was found. Them more information you post the better chance you have of getting a correct ID. Try the Australian wild mushroom hunters page.