Ok, so that's fairly cool in and of itself, but this mushroom's physical characteristics are only a fraction of its awesomeness. The fullness of its coolness, at least in my opinion, comes from the places that it grows.
In three isolated sites in Japan, these mushrooms grow on the stumps and dead roots of oaks.
In a few counties in Texas, they grow on the stumps and dead roots of cedar elms.
That is the same exact organism, feeding on two entirely different food sources and separated by the largest expanse of open water in the world. They've been separated this way for at least 19 million years, so that pretty much rules out human intervention.
People like to propose theories in situations like this, when the natural world shows us something so wonderful and strange it makes our brains hurt, but I just don't feel that need. Instead, I'll just end the story here.
You have questions? That's good. May your life be always filled with more questions than answers.