Marasmius oreades
Also called scotch bonnet, fairy ring champignon.
The fairy ring mushroom grows in rings and arcs in lawns and pastures, often marked by a circle of darker or dead grass. It is one of the most common lawn mushrooms, and it shares that habitat with the toxic fool's funnel.
The tell
Tan, bell-shaped caps in rings in grass, widely spaced gills, and a tough, wiry stem that twists without snapping.
Field marks
Cap, underside and stem show in a photo. The spore print does not, and it is often the deciding check.
Where and when
Lookalikes
Each card says how to tell the two apart.
Clitocybe rivulosa
Photo coming
Clitocybe rivulosa
Fool's funnel is white to buff with a frosted look, and its crowded gills run down the stem. It also grows in rings in grass, sometimes mixed in with fairy ring mushrooms. It contains muscarine.
Pholiotina rugosa
Photo coming
Pholiotina rugosa
The fool's conecap is a fragile lawn mushroom with a brown cap, a ring on the stem, and a rusty brown spore print. It contains amatoxins.
Panaeolus foenisecii
The haymaker's mushroom has a fragile stem that snaps easily, crowded brown mottled gills, and a dark brown spore print.
More side-by-side comparisons
Edibility
Field guides list the fairy ring mushroom as edible. Guides stress the widely spaced gills, tough stem and white spore print, because lawns also produce the fool's funnel, which contains muscarine, and small brown species with amatoxins.
This page states what field guides record. It is not advice to eat, taste or handle anything, and a photo cannot settle edibility. If someone has eaten a wild mushroom that may be toxic, call poison control (1-800-222-1222 in the US) right away, before symptoms start: the deadliest species act hours later.
FAQ
Marasmius oreades is listed as edible in field guides. The risk in lawns is confusion with the fool's funnel, which also grows in rings and contains muscarine, and with small brown mushrooms such as the fool's conecap.
The fungus spreads outward in a circle from a central point, feeding on soil organic matter. The grass at the advancing edge often grows darker and faster, while the zone just inside can thin or die, and the mushrooms appear along the ring after rain.
Fairy ring mushrooms are tan, with widely spaced gills that do not run down the stem and a tough stem that twists without snapping. Fool's funnel is white to buff, with crowded gills that run down a short stem.
Sources
MushroomExpert.com
Missouri Department of Conservation
MykoWeb, California Fungi
Index Fungorum
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