Les français ... naturellement.

The origin of the word "mushroom" is the French "mousseron" which refers to a certain type of fungus. At some point the connection "got lost", i.e. the English did not understand it any more, but the word stuck.
When you posted the image of that Latvian coin, I was surprised first - after all, mushrooms can be found on many medals (token of luck) and postal stamps. Surely there must be more coins with mushrooms? Hmm, maybe not ...
Christian