Fairy rings: a shape drawn by hunger

Fairy rings are one of the few natural phenomena with both a rich folk literature and a rich peer-reviewed one — in both cases for the same reason. They are too regular to look like an accident.

In a review published in 2025 in IMA Fungus, Maurizio Zotti, Giuliano Bonanomi and Stefano Mazzoleni gather what is known about them and open with a sentence that captures the matter: fungal fairy rings have intrigued people and scientists for centuries. They occur in grasslands and forest habitats, and are most often visible as circular distributions of altered vegetation.

The basic mechanism is not disputed. Mycelium grows out from a single point, radiating in every direction and degrading the organic matter of the soil as it goes. Fruit bodies appear at the front of that growth, which is to say at the circumference, and so arrange themselves in a ring. The centre stays empty.

The argument that has run since the nineteenth century concerns two other questions, and the review states them plainly: why the fungus forms a ring rather than a disc, and why its effect on vegetation is sometimes destructive and sometimes stimulating. The first question is about shape, the second about consequence.

The authors propose a model in which accumulated self-material—including DNA—and autotoxicity help explain why mycelium leaves the centre. It is not one mechanism demonstrated for every species. Resource patterns, soil hydrophobicity, phytotoxicity, plant stimulation and habitat conditions can all contribute to the visible ring.

The second question has acquired a proper typology. In a study published in 2026 in Environmental Microbiome, a team working on alpine meadows of the Tibetan plateau divides rings into three types according to their effect on neighbouring plants: type one causes extensive damage, with wilting and necrosis, type two promotes growth, and the third sits in between. One species of fungus can therefore kill the grass while another fertilises it.

Sometimes both effects appear in a single ring, one behind the other. A study of the fairy rings of St George's mushroom, Calocybe gambosa, published in 2025 in Plants, describes exactly that arrangement: a zone of dead vegetation corresponding to the underground mycelial front, and behind it a greener belt where plants do better than anywhere else nearby. Plants just behind the front live on what the fungus has broken down. Plants on the front lose to it.

The reach of the phenomenon is not confined to one species or one climate. The same Neapolitan group described in 2025, in FEMS Microbiology Ecology, the fairy rings of Agaricus urinascens in a species-rich montane Mediterranean grassland, combining vegetation analysis, soil chemistry and next-generation sequencing. The conclusion concerns not the fungus alone but the whole system: rings rebuild soil, plants, fungi and bacteria at once.

It is worth returning now to the folklore, because in this light it stops being mere superstition. The folk explanations of rings — a dance of fairies or witches, a lightning strike, the track of a dragon, the work of moles — share one feature. All of them assume a point event. Something happened in one place and left a mark. That reasoning is essentially correct. The event was a single spore, and the mark is decades of growth.

Because rings are also a clock. If mycelium grows radially at a more or less constant rate, then the diameter of the circle reports its age. The largest known rings measure hundreds of metres across, which means colonies older than many of the trees standing near them. Looking at a ring of mushrooms in a meadow means looking at one organism that has been there longer than everyone who has ever seen it.

That the questions of shape and of consequence can now be put quantitatively is shown by a paper published in 2023 in Scientific Reports. Its authors built a process-based model of plant-fungus interactions and showed that it accounts both for ring types and for their dynamics over time. That is a real change of status: a phenomenon that carried many competing hypotheses for a century and a half now has a model that reproduces the observed patterns rather than merely describing them.

A study published in 2026 in ISME Communications deserves separate mention, because it shows something single observations cannot. The team compared the rings of three species growing side by side in one ornamental grassland at the Royal Palace of Caserta — the fairy ring champignon, Amanita vittadinii and Clitocybe collina. If three species in the same place, on the same soil, produce three different outcomes, then the outcome is decided by the fungus and not by the conditions. This is exactly the kind of experiment nobody can design. It has to be found.

And from that comes the last observation, perhaps the most interesting. The folk name assigns rings to beings that dance in a circle and vanish by morning. The reality is the reverse: this is the most persistent inhabitant of the grassland, not the most fleeting. The only thing that vanishes by morning is the fruit bodies — that is, the one part we are able to see at all.

A model, not a final verdict

Zotti, Bonanomi and Mazzoleni’s review recorded 121 taxa forming fairy rings in natural environments; most are basidiomycetes, but examples among ascomycetes were also found. A ring is the visible trace of a radially advancing fungal front, not the same phenomenon as the arid-land “fairy circles” of Namibia or Western Australia, which are not caused by fungi. The crucial qualification concerns mechanism: this publication is a review that proposes a functional model, not proof of one explanation applying to every species and habitat. In that model, self-DNA accumulation and autotoxicity help explain mycelial dynamics, while the vegetation pattern reflects interacting effects of soil hydrophobicity, phytotoxicity and plant stimulation. The authors explicitly leave questions about species specificity and environmental conditions open. The article should therefore describe “abandonment of the centre through self-DNA” as an evidence-synthesising hypothesis rather than a universal established fact.