The cmbination of spores traveling great distances naturally with species introduction through human travel and direct interference means finding similar gobal species is not uncommon.
Oh? Is this a general statement? I could imagine the species having a common ground but then local peculiarities. No?
Oh totally - they are constantly reproducing with each other, and as genetic testing becomes more common place many mushrooms previously thought to be the same species have been revealed to technically be a series of genetically distinct but closely related species instead.
Plus, even if the species are genetically identical, there can be a ton of differences in the chemistry of the mushroom itself dependent on where it grows. For instance, G.esculenta contains deadly toxins when it grows in some environments and yet appears not to contain those same chemicals when grown in other environments.
Even the A.muscarias - the red, white dotted mushrooms at the top of this post - are alleged to have very different effects on people who ingest it depending on where they are grown - with anecdotal stories of North American A.muscaria potentially having a very different mycotoxin than the same species grown in Siberia. I don't think anyone much cares to test this at the moment, but it's entirely plausible that comparing A.muscaria from Siberia and North and South America might show three genetically distinguishable mushrooms, or, three genetically identical mushrooms with very different mycotoxin profiles.
There's lots of examples of this sort of thing that I might be able to wrangle into a post on its own - but as a general statement, yes: between the ability of the spores to travel great distances and direct human interference in ecosystems, you can find a great many identical or near identical fungal species all over the world.
Thanks a lot for the explanations. I agree you should write full posts on that (in due time of course) in the future. This is very interesting, even for a physicist like me ;)