fairy ring

noun

1. any of numerous mushrooms of meadows and open woods, especially the well-known Marasmius oreades, that spread in rings originating from mycelial growth: formerly supposed to mark the paths laid by dancing fairies.

noun

1. a ring of dark luxuriant vegetation in grassy ground corresponding to the edge of an underground fungal mycelium: popularly associated with the dancing of fairies: seasonally marked by a ring of mushrooms
2. short for fairy ring mushroom, Marasmius oreades, a dainty buff-coloured edible basidiomycetous fungus, characteristically forming rings in grassland