My brother found this “fairy ring” behind his new house in University Heights, Ohio.  According to folklore, these pop up where fairies danced the previous night during a full moon.  (By the way, tonight there’s going to be a bright full “wolf” moon.)  The more likely explanation of how fairy rings form is fantastic.  Fairy rings are made up of mushroom-forming fungus in the group Basidiomycota.  Basidiomycete fungus have mycelia (singular mycelium) and basidiocarps.  The mycelia are the fungal “roots” and function to absorb underground nutrients.  The basidiocarps are mushrooms (or toadstools) and function in reproduction, eventually producing spores that fall from their gills and eventually grow into new individuals.  A spore can fall in a spot and grow outward, expanding its mycelia in all directions in a ring like fashion (fungal mycelial growth is about 10 inches per year).  When the conditions are favorable like just after a rain, mushrooms (basidiocarps) sprout up, sometimes in a few hours, forming a ring.  Fairy rings can get quite large, like this example from the University of Tennessee at Knoxville.  (Some fungus can expand to 2,000 acres and live for 2,000 years!)  Based on its size - radius of about 50 inches - my brother’s fairy ring is maybe about 5 years old.