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, but this is no field, just a grassy verge near trees at the side of the road! 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.
*Update Note (Sep 2011): I’m still thinking there could be a chance they were ‘Agaricus pilatianus’ which are extremely 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