Identifying a field mushroom

 

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.  and inedibles and lookalikes

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The fungus that we know in Australia as a field mushroom is a member of the genus Agaricus.  This is a large genus with a single ancestor (monophyletic) and within the genus is a number of sections each containing a range of species.  While it is tempting to try to assign a species name to any mushroom that you might find, this can be difficult in Australia because many of the species are undescribed or if they are described they aren’t reported in popular guide books.  In addition, it might require the use of a microscope and other detailed analysis.   For our purposes though, it isn’t important to have a name; edibility can be determined by features that can be simply observed.  Our main objectives are:

  • make sure we have an Agaricus
  • Make sure it is not in the section Xanthodermatei

Examples of some well known members of the Agaricus genus are:

Agaricus bisporus – the classic small supermarket mushroom

Agaricus bitorquis – marketed as a larger form of supermarket mushroom

Agaricus avensis – the almond mushroom or horse 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.  Both the colour and texture of the cap are influenced by the environmental conditions as well as the genetics.

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.  ‘Not black, but dark brown. Never eat a mushroom with white gills.  This eliminates the poisonous Amanita and Chlorophyllum.

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, not black or purple or white.  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.

The point of separation should be between the top of the stem and the flesh of the cap.  In some species the stem appears to break away cleanly, but close inspection will show that there is a piece of the flesh from the cap attached to the stem and the position of the separation is actually between the surface of the cap and the flesh of the cap.

This test serves to separate Agaricus from members of the family Cortinaraceae, such as Hebeloma, Inocybe, Cortinarius and Galerina, some of which are seriously poisonous.

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, coal tar soap, creosote or sometimes described as ‘chemical’, then it should be rejected.  Another common product that has the phenol smell is wheelie bin cleaner.  It contains cresols, which are related and smell the same.   Interestingly, and I don’t know why, at high dilutions wheelie bin cleaner smells like clag glue.

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 as will the almond smell. If you can’t reliably and comfortably identify the smell, preferably with confirmation from someone else, then you should reject the mushroom.

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.

Why is phenol a problem and benzaldehyde isn’t?   Because phenol causes acute irritation of the gastrointestinal tract.  This can cause distress and vomiting, but it will pass and will not leave any permanent damage.  Benzaldehyde is a natural product that is a component of almond essence that is used in making marzipan and is without any toxic effects at the doses involved in mushroom consumption. Similarly, benzyl alcohol has low toxicity.

Some poisonous species contain hydroquinone as well as phenol.  This too can also cause gastric upsets. In these ones, both the phenol smell and the yellow colour are not as intense.  The smell should be determined on a fresh specimen at the base of the stem.

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. xanthodermus, 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. Another term for yellow staining is ‘flavescent’.

The place to determine both the colour and the smell is the base of the stem.  Both features are less prominent in other regions of the mushroom. Don’t be shy, really squash it to get the smell.

Another feature of the yellow staining inedible species is that the yellow colour changes to brown over about an hour.  The yellow colour also intensifies with cooking.  Another test is that the colour intensifies and stays permanent in response to a drop of a 10% solution of potassium hydroxide or the more easily obtained sodium hydroxide which does the same thing. Here is a picture of a mushroom that has been tested with sodium hydroxide.

yellow stain with caustic

Yellow stain enhanced with 10% sodium hydroxide solution

 

 

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.

Don’t pick and eat mushrooms that grow beside highways or other places where they may have accumulated things like heavy metals or other potentially toxic things.  Mushrooms can be quite good at gathering these things.

8.  Cap shape

Mushrooms of the section Xanthodermatei, the yellow-staining, phenol containing species tend to have a flat top when juvenile, sometimes continuing to when they are fully grown.  They are often described as having a ‘boxy’ shape.

This, however is not exclusive to this section.  There are many other species that have a similar flat top, and the classic example is Agaricus augustus, known in the US in particular as The Prince, and highly prized as an edible.  So the flat top has limited value as a diagnostic tool.  Sometimes people declare mushrooms to be yellow strainers and therefore inedible based on shape alone without even testing for a yellow stain and smell.  I suggest taking a more thorough approach as outlined above.

9. Tasting

If you are eating an Agaricus that you have never eaten before, try out a small piece first. Sometimes we can be allergic to mushrooms for no apparent reason.   If it tastes horrible, don’t eat it!  This has happened to me with something I expected to taste good.   If you have not experienced any ill effects by the next day, then you can move forward to eating a larger quantity.

Whatever you do, don’t gulp down a huge meal of something that you are unfamiliar with.

10.  One final thing

If, after reading all of the above, you are still not sure, then there is an old mushroom gatherers maxim that applies:

If in doubt – chuck it out

Peter Donecker

47 Responses so far »

  1. 1

    jj said,

    thanks for this Morrie.
    I realise how basic it is, but as a beginner it is vital.

    Four years ago I misidentied what I thought was a VERY familiar regular mushroom which tasted unexpectedly “metallic” and was VERY unwell.

    I had no idea there were so many that could be confused.

    • 2

      morrie2 said,

      The metallic taste is an interesting one, jj. It can come from cooking otherwise edible mushrooms in an iron vessel. There is a reaction that happens that causes a compound with a metallic taste to form. It is incredibly persistant and very unpleasant. The compound is 1-octene-3-one. It is the compound that gives stainless steel a smell when you touch it.

      I have made mention of it with regard to Coprinus comatus, after I had an unpleasant experience with those.

      This might be what you experienced.

  2. 3

    Left Hand said,

    Coprinus comatus are very tasty.

  3. 4

    paula said,

    Thank you so much. I just picked a bagful- now I know I can eat them!

  4. 6

    monica said,

    we found a big mushroom in our garden today, it measures 30cm x 20cm and weighs 370grms, is this big or what????

  5. 9

    Julz said,

    What a gift to come across this comprehensive info. For my homeschooling kids.
    Thanks

  6. 11

    MrSpikie said,

    Morrie, by any chance have you encountered a Death Cap first hand? I’am reading & watching news snippets that they can easily be mistaken for a field mushroom, can you give any advise, many thanks in advance. A great and wealth of knowledge blog by the way.

    • 12

      morrie2 said,

      Yes, I have encountered them first hand, but in France, not in Australia. The main problem with these is people of Asian origin mistaking them for Volvariella or straw mushrooms. They have white gills, a greenish tinge to the cap, a bulb at the base and they grow in association with introduced trees such as oak trees. If you follow my guide there is no chance you will mistake them for Agaricus.

  7. 13

    […] Are these mushrooms picked from the block.  We are so lucky to have a patch growing underneath an Acacia Baileyana only a few feet from our house.  This time of the year, I regularly go out with a bowl and pick enough for dinner. For those of you worried about identification of edible mushrooms, I highly recommend Morrie’s blog,  Tall Trees and Mushrooms  and, in particular, his post Identifying a Field Mushroom. […]

  8. 14

    Owenfox said,

    Thank you for the article my friend. Helpful. Ive done many many many hours of research on mushrooms the last week, and have eaten some nice wild ones I was sure of. Today I picked on that is VERY similar to a field mushroom (it may be), but there is no ring. It seems to be fully developed in that the cap is angling upwards around edges and cracked a little. Gills are deep chocolate brown and it smells very mushroomy like Field mushrooms are supposed. The stalk however is not so thick like others ive seen on the internet. Also the top of cap is whiteish/light brown which can be kind of seen also as a slight bronze/gold tinge (bronwy really). Stalk and cap separate fully like field mushroom.Cap is about 4-5 cm across in diameter. Any thoughts if it’s a field that has lost its ring due to age, or is it too small in cap/stalk and absence of ring making it a lookaike? (which i couldnt find any on the net which are). THANK YOU! Sorry to bother you with all the info. Hoping someone might know! Thank you, Owen🙂

    • 15

      morrie2 said,

      Hi Owen,

      It isn’t really possible to offer an opinion about identification over the internet.

      I have not mentioned rings in my guide for a couple of reasons. One of those is that rings are sometimes absent or at best obscure. The other is that some very deadly species like Amanitas have rings.

      It is best to observe the mushrooms in all their stages if you are in doubt. You will become familiar with them in time. Until you are sure, abstain.

      Cheers,
      Morrie

      • 16

        Owenfox said,

        Thanks Morrie! I believe it to be a field mushroom simply at late growth. The deep mushroomy smell, browny white/creamy cap and chocolate brown gills suggest so. But I won’t eat it for now until I gain a little more info. Only got one mushroom anyway😛 ha🙂 Thanks!

  9. 17

    Graeme Smith said,

    I have just picked from my old veggie garden a big bag of mushrooms, nice white tops pink underneath, I have read your information, and will make a nice sauce to have with my steak, thanks for the information, Anne smith byron bay

  10. 19

    siddsainty said,

    Reblogged this on the.urban.forage and commented:
    Awesome guide to foraging wild fungi. I’m working on my own identification chart myself which will be up soon. I found this as a helpful introduction and basic rule guide to Australian fungi. However this is provided as a guide only. Only ever consume fungi if you are completely sure of the species.

  11. 21

    Pencho said,

    One of the safest test I have used when picking mushrooms in Europe is to hand them to a goat or sheep. If mushrooms are edible the animals will eat them as fast as they sniff them. If they don’t like them, the mushrooms are no good to you too.

    • 22

      morrie2 said,

      A perfect example of a piece of ‘folk wisdom’ that could have potentially lethal consequences. Animals have no innate judgement about what is poisonous and what is not, nor do they necessarily have the same metabolism as we do. As an example, sheep in Australia often die from eating poisonous plants of various sorts, including the wide range of pea flowered plants known collectively as “sheep poisons”. These contain 1080, a poison that is used commercially to kill wild dogs. It has killed thousands of sheep.

      Seaweed will similarly kill many sheep.

      Reindeer eat Amanita muscaria, which though not necessarily lethal can cause very unpleasant side effects. So do squirrels.

      In my article on Ramaria you can read about cattle deaths in Brazil from eating that genus of fungus.

      If you want to trust your life to the judgement of a sheep or a goat, or any other animal, go ahead, but I count my human intelligence as higher than those animals.

  12. 23

    Keith said,

    Hi Morrie2,
    I have just moved to a new area south of Brisbane and have these great looking mushrooms popping up all over the place due to the huge rain fall. N the ground they have white gills but over night after picking they turned brown. Still not sure as never been down this road before. Is there a way I can send you a couple of pics that may help clarify what I have here?
    Keith

    • 24

      morrie2 said,

      Hi Keith,
      You can load the pictures onto a host such as photobucket and then post a link here. I have had mushrooms go through the same change.

      Morrie

  13. 25

    Keith said,

    Hi Morrie,
    Thanks for that I will try and work out what photo bucket is and do my best to send them to you.
    Keith

  14. 26

    Geoff said,

    Hi Morrie,

    I have these growing over our paddocks whenever it rains but am always concerned about what type they are. Can you tell from these photos…this one is 16cm across the cap and growing in open paddock…not in cow poo. Will leave this one in office to see if gills turn dark, but I’m sure they do from memory. Thanks heaps!

    • 27

      morrie2 said,

      Hi Geoff,

      Those are definitely not field mushrooms. They are either a Macrolepiota or Chlorophyllum. I suspect that you will find a green tinge to the gills if you look closely. My advice is to leave these alone.

      Cheers,

      Morrie

  15. 28

    Sharnie said,

    Hi Morrie, I’ve really enjoyed your article on Field Mushroom identification, I believe I’ve got exactly that growing in my front Lawn in Mudgee NSW – they match all of your descriptions from tops/gills/smell/stems/substrate. What do you think? I’ve tried to attach a picture using photo bucket for the first time:

    Regards Sharnie

    • 29

      morrie2 said,

      Hi Sharnie. I am sorry that it took so long to reply. I missed your comment.

      Those do indeed look like an edible Agaricus. If they pass all the tests as you describe then they should be ok. As always, I suggest that you try a small portion first, perhaps fried with a little butter in a pan. If the taste is ok, then I would have no problem eating them.

      • 30

        Sharnie said,

        When I didn’t hear back from you in April Morrie I went ahead and tested a little morsel and then cooked up the rest – they really were delicious. With my new found knowledge I’m scouring my neighbours yards for more, they all think I’m mad (I hope it stays that way – more for me)

  16. 31

    Jane Morrow said,

    Hi Morrie, Fabulous blog.
    I would like to try establishing a field of field mushrooms have you any suggestions on how to achieve this?

    • 32

      morrie2 said,

      Thanks Jane.
      I would like to do something similar but I haven’t really addressed it yet. Firstly, you would need a field that has not been subject to chemical fertiliser, especially superphosphate. This is why we don’t find too many mushrooms in paddocks any more. It would need to contain plenty of humus too. Additions of animal manure over time should assist.
      As far as inoculation, the simplest way might be to carefully extract a section of soil from an existing location where they occur and transplant this to the new location. A piece about the size of a brick should suffice. You could try making your own spawn, but that is a little more involved.
      Cheers,
      Morrie

  17. 33

    narf77 said,

    I just used your excellent site to identify and “pass” some field mushrooms that I found on the oval whilst walking the dog today. They passed the stem/cap snap test, the gill colour test, the top test and the “sniff” test (still smelled mushroomy after I cooked them) so I ate them. They tasted wonderful. Thank you for sharing your knowledge with us all. I remember picking and eating mushies as a kid all of the time. No-one told us that they were poisonous and I dare say our parents had been eating them for ages as well. I live in Tassie now but come from Denmark W.A. Again, cheers for sharing your knowledge about mushrooms. My stomach salutes you🙂

    • 34

      morrie2 said,

      Thanks for your kind comments. I am glad that you found it useful.

      • 35

        narf77 said,

        Trawling through your wonderfully informative blog made me homesick. I have tucked your blog into my RSS Feed Reader and will get to read every new post you post. Thank you for your excellent article. I am still alive!🙂

  18. 36

    gopal said,

    Hi, do you know of any skilled foragers in the northern rivers region of nsw. Mycelium is an integral part of my garden Forrest eco system but I’m unsure what are the edible and inedible species we are currently growing. I’m slowly building some amazing mushroom patches and compost piles it’d be great to be harvesting not only compost but food from this cornerstone of my garden ecosystem. I really don’t want anything to do with the magic variety’s

  19. 38

    Leanna said,

    I’m puzzled by the instructions never to eat a mushroom with white gills. Oyster mushrooms have snowy white gills.

    • 39

      morrie2 said,

      Hi Leanna,

      That comment was really for people who are looking at something that they think might be an edible Agaricus and so are using the guide to make a decision.

      Cheers,

      Morrie

  20. 40

    Emilija Saleta said,

    Thank you so much for this information. I have had ‘suspected’ field mushrooms in my yard for a few years now and now that I have found your tests, they have passed with flying colours. I know what to look for. I’ll still be testing them all individually though before I eat🙂

  21. 41

    Alanna said,

    I know this is an old post now, but just want to thank you for such a comprehensive guide! I have avoided eating the mushrooms that crop at the edge of my lawn the last two winters, because they always just looked a little iffy … this afternoon I found such a gorgeous looking specimen that I immediately wanted to eat – and as it (and all the others I’ve rejected) adhere to your recommendations, I feel safe giving it a test. Much appreciated!

    I know there are some just across the road from my house, so might have to investigate those, too!

  22. 43

    foodledoodle said,

    Hi Morrie this is an amazing website.Do you take field trips to show groups how to identify local fungi?-Andrew

  23. 46

    Val said,

    Can I assume that if I ate it (a decent serve), with not the slightest hint of a belly ache, it is safe.
    i have (or had in winter) a fairy ring – did all your tests and concluded it was probably agaricus campestris
    The fairy ring was in paddocks and the soil under cherry trees.
    A forager i met told me that if it was growing under trees it wouldn’t be agaricus
    Is this correct?
    It was definitely growing in soil, not wood.

    • 47

      morrie2 said,

      Hi Val,

      If you ate it and it didn’t make you sick then that sounds like a good sign to me. Of course it is important that they taste good too!

      It is very difficult to give names like Agaricus campestris to specimens in Australia as it is a huge genus and many species here are not described.

      As to them not occurring under trees, that isn’t really correct. I have found them under trees many times and in fact the most delicious Agaricus I have ever found was in a pine plantation. It is more a precautionary thing. The deadly Amanita phalloides and other poisonous species occur under deciduous trees and it is wise to very cautious if there are deciduous trees in the area.

      Cheers,
      Morrie


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