While green plants supply the bulk of oxygen to our atmosphere, forest fungi such as mushrooms nurture our soil by leaving behind a residue of decomposed organic remains enriched in nitrogen and phosphorous. Presumably, in medieval times they served as playgrounds for fairies on moonlit nights. The mysterious overnight appearance of mushroom clumps may have added to the legend. Fairy circles can often be seen on freshly mowed lawns, even though no mushrooms appear at the surface. They are identified by rings in the grass which mark the fertile outer perimeter of the growing circle.
Fairy rings can grow to impressive dimensions.
Aerial photos have revealed rings measuring 200 yards in diameter that are thought to be hundreds of years old.