The Secret of Fairy Rings

Numerous species of mushrooms draw on the ground circles which have, at all times, intrigued. The story begins with a spore germinating and releasing underground filaments, the hyphae. Hyphae constitute the very substance of the mushroom and form network underground in search of food. If nutrients are uniformly distributed all around, the network extends in all directions at a rate of a few centimeters to one meter per year, depending on the species. As food becomes scarce in the middle of the web, the area dries out while the periphery expands farther. The expansion continues for years, sometime for hundreds of years.

The fairy ring mushroom is but one of hundreds of species following the same pattern. Most of them are decomposers, recycling organic matter: puff-balls, psalliotas, lepiotas, ... In the Blue Mountains of Oregon, a single common armillary (Armillaria solidipes ) covers 1 000 ha: all its cells are genetically identical and have been coordinating their search of food for more than 2,400 years.

Other species do not limit themselves to decomposing matter, they exchange nutrients with the surrounding vegetation in a mutually beneficial relationship. Many of these symbiotic species, such as common chanterelles or truffles, occasionally form circles, but they can not move too far away from their life partner, usually following the expanding roots.