It’s a Sunday afternoon and I pass by a grass verge near my house. My heart jumps at the sight of a huge cluster of (what seem to be) Horse mushrooms or possibly Field mushrooms. I was without a basket or bag so like a kid in a sweet shop I scooped up a good share, leaving some to drop their spores.
But my dreams of a nice fry up or even a creamy mushroom soup are soon quaffed because I suddenly realise these mushrooms are not what they appear to be. I wait until I get home around the corner to double check. Read on…
I’m not surprised at all that the Yellow Stainer (Agaricus xanthodermus) is responsible for the most cases of mushroom poisoning in this country. Although this evil twin of our favourite field, wood and Horse mushrooms is not deadly it can keep you in the loo for longer than you normally do! Gastric symptoms can persist for up to 24 hours. Fortunately I have not been caught out yet, but some people after consumption usually get away with only mild upset or sometimes have no reaction at all. My Uncle once told me “Ooh, I don’t get along with those Yellow Stainers – don’t like ‘em” . Let’s hope that it was only his palette they offended – I didn’t ask!
So how on earth can I identify this poisonous peril when compared to a Horse mushroom? I hear you all cry! (see also update note below)*
Don’t rely on the ‘overall look’. They differ in colour from pure white to brown/grey, scaly and smooth, tall and short and so on. Horse mushrooms can display some yellow colour on their cap and stem – so if you do see some yellow it’s not always a bad thing.
Both the Horse Mushroom and Yellow Stainer ‘bruise’ yellow (There’s hardly any yellow about the Field mushroom). But the Yellow Stainer has a stronger chromium yellow once bruised. If you rub the cap with your thumb, there will be a very noticeable colour change. But the crunch test for me is at the very base. Take a knife to the very bottom of the stem (the base is more bulbous than the others) and cut in half (see picture below). If the colour changes to a vivid yellow, then you’ve got yourself a Yellow Stainer. Horse and Field mushrooms do not stain at the base like this.
Other good ID tips are:
1. The smell is an unpleasant (phenol/inky smell more apparent when being cooked)
2. The ring on the stem is large and floppy.
3. Before the veil drops it does not have the ‘cogwheel’ pattern like the Horse Mushroom.
4. Gills when very young are white unlike the Horse and Field mushrooms which are pink
In addition to point 3 – if you’re new to collecting mushrooms, avoid very young specimens as they also can be confused with much more poisonous (even deadly) young toadstools.
Horse and Field Mushroom lookalike - The Yellow Stainer
On open caps: The ring on the Yellow Stainer is noticably large and floppy. The Field Mushroom's ring is a fine torn frill. The Horse Mushroom's ring is formed of a double membrane. The lower part is 'star shaped'
*Update Note (Sep 2011): I’m still in a quandry as if to what I found was possibly ‘Agaricus pilatianus’ which is extemely similar to the Yellow Stainer (and in the same family) but has no authenticated recording in the UK and is rare in mainland Europe**, and there are similar/variable species to consider. The cloudy brown cap and mature ‘chocolate’ coloured gills (see above middle-right picture) are two good markers that point to a variant. But variants and similar species can poison in the same way as the Yellow Stainer, if not more so. So ‘either/or’ it is simply best avoided. So, beware of bright yellow…
** Reference: Roger Phillips Mushrooms book 1996
Yes – these little blighters are so similar – we ate them by accident last night, but I’m relieved to say that we had no adverse effects from them. If you find that they turn a real yellow when cooking, then discard them immediately!
Glad to hear you were OK. That’s also a good tip on what to look for when cooking. I haven’t eaten any – do they taste any different to a horse mushroom?
The inky (phenol) taste is unmistakable (although the regular mushroom taste is still there underneath). On cooking the phenol smell becomes stronger and they do become very yellow.
I nibbled a raw one experimentally as I was so certain it was a horse mushroom. i didn’t suffer any ill effects – either because I’m immune (some are) but more likely because I didn’t eat enough.
I picked over 1 kilo of what I thought were Horse Mushrooms on a walk last Friday and had plans to make some delish soup when I got home, I know Horse Mushrooms stain yellow but decided to check in my Mushroom Book by Roger Phillips, having a small doubt in my mind I started searching on the net and found your site.
Unfortunately I have a habit of breaking of the stem half way down a throwing the dirty bit away so that the rest of my “Booty” does not get soil on, so having read your list of things to look for to tell the difference between Horse and Yellow I did not have a vital piece that I needed.
I had picked some not very far from where I live so off I went to get a couple more, when I cut the whole of the stem in half it went yellow at the very bottom, feeling disappointed I threw the lot in the bin.
Last week I ate some that I had cooked, they did go very yellow but I assumed that was because I cooked them in butter, although they did not taste great they did not taste very unpleasant either, thankfully I too did not suffer any adverse effects.
Is it my imagination or does there seem to be lots of Yellow Stainers about at the moment?
Good point on the smell. I have not been on the receiving end of the cooked smell since I have not cooked any. Phenol is the predominant chemical in these mushrooms along with a few other nasty chemicals, but not in volume that are life threatening. Thanks for the comment. It’s good to know in case anyone gets to the cooking stage – it’ll be a last warning!
I understand what you’re saying. I myself piled in to a massive stock of what I thought were field or horse mushrooms! I even have a photo of myself with the catch. But now I’m too embarrassed to show it after realising the true nature of my discovery! It’s always best to get the ‘whole’ of the mushroom, base and all, to help in identification. I know how easy it is to get carried away in picking mushrooms.
It’s true though! The ratio in my Yellow stainer/Horse or field mushroom discoveries is 3:1
It’s also interesting to note that 2010 so far has been an exceptionally good year for mushrooms – we’re going to get loads of different species at all times. The desirable are going to be as common as the undesirable.
Picked some mushrooms that I was fairly sure were horse mushrooms this p.m. The location was on a scarp slope of kentish chalk downland. I have gathered genuine horse mushrooms from a location within a few hundred metres of this site (but under some hawthorn trees, unlike these which were in open field/grazing pasture) in the past and enjoyed their delicious flavour so was pretty sure that these would be the same species. However, it is late in the season and it has been cold and fairly dry so these examples were immature and small. Nearby were some that had rotted and were maggotty and they certainly looked like horse mushrooms. However, although to me they smelt good enough, my specimens went a bright yellow when cooked (I don’t remember this with my previous encounters with horse mushrooms). I am still not entirely sure which species I found because they were so small – gills were a pale beige/pink and the cap was white with a beige tinge on the slightly larger specimens. I decided to discard them to be on the safe side.
I sympathise with your frustration. Sometimes Yellow Stainers don’t smell that bad to me although not holding that strong, typical mushroom smell. There are many Agaricus species out there, obviously some more common than others, but even a few days ago I found an extremely uncommon species just down the road on a grass verge, looking like smaller versions of Horse mushrooms with a few extra characteristics!
If the mushrooms you found were very young and had pale beige/pink then that confuses things more! Young Yellow Stainers have white gills when young or even pale-pale beige. So they could’ve been Yellow Stainers.
Some Agaricus species have white gills when young and some others, pinkish! And because people don’t report on changes in colour, smell etc. whilst cooking every mushroom (like you good people out there) there is no reliable record of what species you’ve actually got.
If it’s not too late, you could go back to the place you found them and see what they’re like when matured. I sometimes do this and it really helps in identification.
hi, i picked what i thought were field mushrooms yesterday ( nov 25th ) late for mushrooms i know but thought i’d stumbled on a bounty! my husband was looking forward to them with his steak supper. when i picked them they turned yellow ( i dont know anything about mushrooms so thought this was normal) but when i got home the yellow had gone. upon cooking they went very yellow and the smell was very bad. my husband ate one and decided to leave the rest as the taste was “chemical” in his words. luckily he hasnt suffered any bad reaction. lesson learned!!
Glad to hear your husband didn’t suffer any ill effects. The mushroom season has been a little late to reach full bloom, due to the dry weather earlier in the year. November has been a good month for mushrooms this year. Even today (Nov 27th) I found a large group of Yellow stainers again myself.