Agaricus (poss porphyrizon) for ID

[RobSutton]

I found this solitary Agaricus as Malham Tarn - growing under Beech in leaf litter on Limestone. Cap was 80mm diameter and gave a yellow reaction to KOH, the stipe was 13mm x 90mm with distinct yellowing at the base.



On cutting a LS there was some slow and slight yellowing particularly at the base of the stem.



Spores were small 5.3-6.3µ x 3.5-4.6µ:


Simple clavate cystidia were present:


I usually leave Agaricus species well alone as they seem to rely on smell (nothing noted but this was with a seasonally bunged up nose!) and colour (coppery brown - enhanced on drying) neither of which I do easily. Tempted by the new edition of Geoffrey Kibby's Agaricus key I had a go though and got down to Agaricus porphyrizon which is noted as rare and doesn't seem to have been recorded from Yorkshire at least as far as the NBN Gateway site suggests!

Having no real confidence in this group I thought I'd pass it over to WAB's collective wisdom. Any suggestions/help, as ever, is gratefully acknowledged in advance.

[Ditiola]

Hi Rob

I have tried with Geoff Kibby's key. and it could well be A. porphyrizon, however from your photos it is difficult to see the texture of the cap surface, although it looks brown it is not easy to see if this is brown scales or brown spores from another previous cap. It is not easy when you only have one specimen as the differences between species are often quite subtle and a single cap may not be a typical specimen, sometimes when you cut several specimens in half the flesh may change colour at to different degrees.

I would not be put off by a fungus being described as "Rare" as I have found several fungi this year that have only 3 or 4 UK records!

Peter

[RobSutton]

Thanks Peter

I'm pretty sure the cap had brown scales rather than just being covered in brown spores. Agaricus is one of those Genera I've always steered clear of in the past. Geoff's key certainly gives me bit more hope of getting things close to being correct.

[Chris Yeates]

Originally Posted by RobSutton

. . . . . I]Agaricus porphyrizon[/i] which is noted as rare and doesn't seem to have been recorded from Yorkshire at least as far as the NBN Gateway site suggests!

Having no real confidence in this group I thought I'd pass it over to WAB's collective wisdom. Any suggestions/help, as ever, is gratefully acknowledged in advance.

I have never really looked at Agaricus myself; having had conversations with Bert Brand - who specialised in the genus - it struck me as a rather poorly understood genus in which you needed to have a lot of experience before you 'got a grip' on them as it were

I haven't tested GK's key, hopefully it has sorted many of the issues out (one thing that always struck me was the very confused nomenclature)

and you're correct - there are no Yorkshire Agaricus polyrhizon records of which I am aware

one for Kew methinks: pity there's only one - I was taught that a fungus isn't a fungus unless you have at least three of them (but of course that's an ideal we are not always granted)

cheers

Chris