Ordinary British Field Mushrooms are now so rare that if there are any growing in a given area, the locals will be sworn to secrecy! Even in the 50s when organic cow farming (the type of pasture which produces the best mushies) was common, my dad was keen enough to get some from the fields on his RAF base that he risked riding his bike over the runway in the early morning fog in order to get his mushies. Nobody would have seen him sneak off for them - so nobody else would find out his source, but he also risked getting into serious trouble!
And I've just remembered
a post I wrote about the Germanic custom of the Symbel - and it's links to the word Simbelmyne.