Posts tagged Inedible mushrooms

Anatomy of a Yellow Stainer

Within the genus Agaricus, the Section Xathodermatei contains a number of species that are commonly known as yellow stainers and they are known to contain phenol which causes quite nasty gastric upsets if consumed. I have been meaning to put together a post about these but it was only this morning that I found a substantial patch of them on a street  verge to do some images and experiments.  A few members of the patch are shown in the picture below.

Yellow stainers on street verge

 

The yellow staining reaction is seen both on the cap and on the stem of the mushrooms and manifests itself as a bright chrome yellow stain that quickly fades. Once picked, the yellow stain on the cap may not continue to show itself. The picture below shows the sort of stain that occurs when you first pick one of these mushrooms. This was completely gone within 2 minutes.

yellow stain on cap

Yellow stain on edge of cap when first picked

 

The partial veil on these mushrooms has a fluffy appearance that I believe can be called flocculose.   The appearance of the partial veil at various stages is shown in the following set of images.

Partial veil at various stages of growth

The yellow stain on the cut stem can also been seen in these images as can the white core in the centre of the stem, a feature that is also seen in supermarket mushrooms.

Another feature that tends to be a characteristic of mushrooms in this Section is the ‘boxy’ cap shape.   That shape can be seen in the first image above.  This is where the analysis gets interesting.  As I have mentioned elsewhere, the yellow stain can be made permanent on these mushrooms by applying an alkali.  The yellow colour is due to 4,4-dihydroxyazobenzene.    While looking closely at these mushrooms I noticed that they have a very distinct internal structure featuring a very dense section in the cap above the stem.   This is revealed in a sectioned piece developed with Napisan solution which provided the necessary alkalinity and perhaps some oxidizing power that might have had an effect.   An example of a sectioned mushroom developed in this way is shown in the pictures below, compared with a supermarket version.

Yellow stainer (top)  compared with normal supermarket mushroom (bottom), both developed with Napisan solution

In this view it is immediately apparent that there is a significant difference in the internal structure of the two mushrooms.  The hard core in the centre of the cap of the yellow stainer shows up clearly.   I strongly suspect that this structure is responsible for the boxy shape of these mushrooms.   Beyond that however, the flesh of the cap of the yellow stainer remains refractory to the effects of the Napisan while the flesh of the supermarket mushroom saturates and slightly darkens.   The hard core also influences the way the cap separates from the stem.   In the case of the supermarket mushroom the separation is very clean but in the case of the yellow stainer the stem breaks away with a rather ragged edge, as shown in the picture below with two yellow stainers on the right and two supermarket varieties on the left.

Cap separation on supermarket mushrooms (left) versus yellow stainers (right).

I have in mind a few more experiments on these interesting mushrooms but I will finish this post off for now.

A quick postscript.  After about an hour the difference between the two mushrooms became even more stark.

 

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A look-alike Psathyrella

This small cluster of mushrooms appeared recently in a garden bed amoungst some horse manure.

These mushrooms have a white cap with a brown colouration in the middle and when we flip them over, we can see that the gill colour is in the right range.

However, if we try to separate the cap from the stem, we find that we can’t, and the stem is furthermore completely hollow and thinner than what we might expect from an Agaricus.  The mushroom pictured is Psathyrella candolleana.  There is another species more commonly seen in forests called P. aspersopora.  Both are of unknown or doubtfull edibility.

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A look-alike Hebeloma

During another walk this evening I encountered another mushroom that had a similar appearance to an edible field mushroom.   I picked it and brought it back to the house to document why it is not an edible field mushroom.  Here is a picture of the cap.

The cap is not outside of the colour range that one might expect for an edible field mushroom, but notice that it is shiny?  In fact it is quite slimy to the touch.  This alone is enough to declare it to not be an edible Agaricus.  However, let us continue…

When we flip the mushroom over, we can see that the gills are in the right kind of colour range and that the stem has the right sort of thickness in relation to the cap.  In fact, the gills even darken from pinkish to brown over time.   However, the thing that is glaringly absent is an annulus or ring on the stem.  Not a hint of one!  We know for sure now that this is not an edible Agaricus, but lets go further…

If we attempt to snap the stem away from the cap, the result is unsucessful.  The whole cap tears apart rather than breaking at the junction of the stem and the cap.  There is no change in the tissue type between the stem and the cap.  This thing has now failed three tests.  Quite a pretty mushroom never the less 🙂

If you are wondering about the tabletop, it is Australian red cedar, Toona ciliata.  The mushrroom is Hebeloma westraliense, edibility unknown (Bougher and Syme).  Hebelomas are very useful for promoting the growth of Eucalypts and are cultivated for that purpose worldwide.

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