In D&D, fungi are considered plants, which means a fairy circle is a valid target for Transport via Plants.

This is basically the plot to the original Super Mario Brothers movie

I'm pretty sure this is the plot of the first season of Star Trek Discovery.

RuneScape much?

Hold on, Star Trek: Discovery is about Fey?

See, I was always taught the mushrooms were just growing afterwards, wherever a large amount of magic had been discharged (like when a portal happened). They were growing after the fact, soaking up any residual magic splash.