Disclaimer : These notes are provided as a guide only. While every attempt has been made to try to assist in the identification, the risk of eating any wild mushroom rests with the individual and I do not accept any responsibility for consequences that may arise from the action of anyone eating wild mushrooms. See also the Ag department notes, Perth.
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The fungus that we know in Australia as a field mushroom is a member of the genus Agaricus. Examples of this genus are:
Agaricus bisporus – the classic small supermarket mushroom
Agaricus bitorquis – marketed as a larger form of supermarket mushroom
Agaricus avensis – the almond mushroom
Agaricus campestris – the classic if oft mis-identified field mushroom.
This list of features has been put together to assist the average person to identify an edible field mushroom.
1. Cap colour and texture
The cap of the edible Agaricus species varies from white though dun and on to a slightly pinkish colour in species like A. sylvaticus. The cap may be slightly scaley, and may be cracked. It is always dry and is never slimy to the touch.
Any mushroom with any hint of green in the cap colour should be rejected as this is the colour of the deadly Amanita phalloides.
top of small field mushroom, typical of those found in lawns (Dave Freer)
top of large field mushroom, similar to supermarket field mushroom (Dave Freer)
top of Agaricus arvenis, showing scales
A forest mushroom, showing red tones on the top
Top of Agaricus bitorquis. A clean off-white, with undulations
A horse mushroom from the Riverina district of NSW. Note scales.
A mushroom from a backyard in Penhurst, Victoria, showing some radiating spots.
A mushroom from Digby in Victoria, showing red/brown central region and radiating scales.
2. Gill colour
The gill colour may vary from brown to pink or off-white in the young mushroom, but it will always darken to a dark brown in a mature specimen. Never eat a mushroom with white gills.
Pink colour of immature specimen of a small field mushroom. Picture courtesy of Dave Freer.
3. Spore print
The spore print is always dark brown. Not pink, not rusty. Dark brown only.
How do we take a spore print? Easy. Place the mushroom, or a piece of it, on a piece of waxed paper and place a glass over the top, with the edge of the jar just propped up by a matchstick or something similar to allow water vapour to escape. Place in a position away from draughts, overnight.
A simple setup for taking spore print
A spore print of an Agaricus species
4. The stem snaps away from the cap
The stem of an Agaricus has a texture that comprises a bundle of stringy cells running axially. The cap has a different texture. At the point of the junction of these two textures, there is region where the two will break apart cleanly. Try this for yourself with a supermarket mushroom. Note in this mushroom the dark gill colour.
5. Smell
Field mushrooms have a distinctive smell that is either ‘mushroomy’ due to a chemical called octenal, or almond/aniseed due to the presence of benzyl alcohol and benzaldehyde.
If the mushroom has a smell of phenol, which is the smell of India ink, or phenyl disinfectant, or sometimes described as ‘chemical’, then it should be rejected. If in doubt, there are two approaches you can take; 1) put the mushroom in a plastic bag for 15 minutes and then sniff the contents or 2) cook a piece of the suspect mushroom. The bad smell will become more apparent if there is phenol present.
It is often reported that some people can tolerate eating mushrooms that contain phenol. The only stories I have heard of such poisonings have involved the whole group of consumers. I suspect that the truth is that some people report eating yellow staining mushrooms without ill effect, but they have in fact consumed one of the arvenses group rather than one that contains phenol.
6. Colour of cut or bruised flesh
The colour of the cut or bruised flesh may be brown or red or yellow, or there may be no change in colour at all. Here for example is an edible mushroom, Agaricus bitorquis, which is showing red on a cut piece. Photo courtesy of Dave Freer.
Brown or red bruising is ok. A yellow colour may be ok or it may indicate Agaricus xanthodermis, which will cause stomach upsets. There is much confusion about this. The yellow colour is an indicator of A. xanthodermis, which contains phenol, but it does not necessarily indicate an indedible mushroom. For a diagnosis of an indedible yellow staining mushroom, one needs to have the yellow stain in combination with a phenol smell, as mentioned above.
7. Substrate
Field mushrooms will always be found growing from some kind of soil. They never grow directly from wood and they do not grow in the middle of cow pats. There are some deadly species like Galerina that grow from wood and if it is growing from a cow pat, there is a good chance that it is the notorius hallucinogenic ‘gold top’, on the east coast at least. They do not tend to grow from wood chip or bark mulch either.
