KingdomFungiGenusMarasmiusSpeciesoreades
Marasmius oreades
T0 · No known toxinsPublished 2026-09-22late-spring / Summer / Autumn
This is the grassland species that most often gets collected by people who have not learned to test the stem, and it is paired here with the most dangerous white-spored grassland agaric in the temperate zone. The two are genuinely similar in size, colour and habitat. They are separated in two seconds by a test you can do with one hand.
Block 01 · Record
The stem test and the gill spacing
Pick a fruit body and try to twirl the stem around your index finger. Marasmius oreades has a tough, cartilaginous stem that winds around the finger and springs back without cracking. Clitocybe dealbata and C. rivulosa have brittle stems that snap the moment you bend them past about 30 degrees. Back that up with the gills: widely spaced, thick, waxy, with gaps as wide as the blades themselves. Both characters are readable in the field with no equipment, and both are consistent across every collection in a ring.
Hygrophanous caps and the spore print
The striations at the cap margin run about half the radius on a wet specimen and vanish entirely within twenty minutes of picking as the cap dries — this is what hygrophanous means, and it is why a dried specimen cannot be keyed on margin characters. The spore print is white and thin. Spores are 7-9.5 x 4-5.5 micrometres, ellipsoid to tear-shaped, thin-walled, smooth and inamyloid. Melzer's reagent leaves them pale, and cotton blue leaves them unstained.
Rings, and how to read them
The species grows as a ring because a single mycelium expands radially through the grass root zone at a roughly constant rate, exhausting nutrients behind the front and fruiting at the leading edge. Rings in established pasture typically advance 10-30 cm per season, so a ring 3 metres across is decades old. The fruit bodies appear in late spring and again from late August through October, and each ring tends to fruit after rain that follows at least a week of dry weather.
Discrimination: the muscarine clitocybes
Clitocybe dealbata and C. rivulosa contain muscarine at concentrations that produce sweating, salivation, lacrimation, blurred vision and bradycardia within thirty to sixty minutes of a meal, and can be lethal in a small adult at the dose a normal portion delivers. Crowded thin gills, a brittle stem, and growth scattered through the sward rather than in a ring are the three field characters. If you have any doubt about the stem test, do not collect — the pair is not one where a provisional identification is worth the risk.
Points to carry to the bench
- Twirl the stem around a finger — it winds and springs back. A brittle stem that snaps means Clitocybe.
- Gills widely spaced, thick and waxy, with gaps as wide as the blades.
- Hygrophanous cap: margin striations vanish within twenty minutes of picking.
- White spore print, inamyloid spores of 7-9.5 micrometres; grows in expanding rings in short turf.
| Cap | shape: Convex then plano-convex with a persistent broad umbo, 10-40 mm across; the umbo is smooth and darker than the rest of the cap.surface: Buff to tan when moist, fading to pale cream as it dries; smooth or very finely velvety, never scaly.margin: Striate to plicate over half the radius when moist, the striations fading completely as the cap dries — the classic hygrophanous margin. |
|---|---|
| Gills | attachment: Adnexed to nearly free, the gill backs meeting the stem with a small notch rather than running down it.spacing: Widely spaced, 8-12 gills reaching the margin on a 30 mm cap, with gaps between them at least as wide as the gills themselves.edge: Thick, blunt, waxy in appearance and entire; the waxiness is visible under a hand lens as a slightly translucent beading. |
| Spore print | Ellipsoid to tear-shaped in profile, smooth, with a prominent hilar appendix.Smooth, thin-walled, inamyloid; no oil drops. |
| Habitat and season | Saprotrophic in close-mown or grazed turf, almost always in rings; the mycelium grows outward through the root zone of the grass and the fruit bodies mark its advancing front. Same rings return every year and expand by roughly 10-30 cm per season. |
Block 02 · Chemistry
| Reagent | Verdict | Reaction | Weight |
|---|---|---|---|
 MELZ | inamyloid | Spore wall stays pale yellow; no blue-black or rusty development. | 3.00 |
 KOH5 | negative | Cap shows no reaction whatever; the buff pigment is stable to alkali, which is not true of the pale Clitocybe look-alikes. | 2.00 |
 FESO4 | negative | Flesh unchanged after 90 s at 10% concentration. | 3.00 |
 ANIS | negative | No change on the reviving cap; the buff tone reads the same wet and dry. | 2.00 |
 COTTON | acyanophilic | Spores remain unstained, appearing as clear outlines. | 2.00 |
Injury stain None. The cap and the tough stem keep their colour after handling and after cutting. A pale grassland agaric whose stem snaps cleanly and whose cut flesh browns is not this species.
Block 03 · Confusion
| Separating character | This record | Confused with |
|---|---|---|
| Crowded thin gills that touch each other, a brittle stem that snaps instead of flexing, and growth in troops rather than in rings; the stem test takes two seconds and is decisive. | Marasmius oreadesT0 | Clitocybe dealbata▲ +3 |
| Same muscarine tier as C. dealbata, distinguished from it by a white bloom on the cap; separated from M. oreades by the same crowded gills and brittle stem. | Marasmius oreadesT0 | Clitocybe rivulosa▲ +3 |
| Pink spore print and deeply decurrent gills, plus a strong mealy smell; equally T0 but easily separated by the first overnight print. | Marasmius oreadesT0 | Clitopilus prunulus▲ +0 |
Toxicity ladder
No toxin has been isolated or reproduced in feeding trials, and decades of documented ingestion carry no reproducible syndrome. T0 is a statement about the chemistry of the species, never a statement about a specimen in your hand.
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