Agaricus arvensis
species of fungus
Agaricus arvensis, commonly known as the horse mushroom, is a mushroom-forming fungus of the genus Agaricus.
Taxonomy
It was described as Agaricus arvensis by Jacob Christian Schaeffer in 1774, and given numerous binomial descriptions since. Its specific epithet arvensis means "of the field".
Description
The cap is 7–20 cm (3–8 in) across, whitish, smooth, and dry; it stains yellow, particularly when young. The gills are pale pink to white at first, later passing through grey and brown to become dull chocolate. A large, spreading ring has white above, but sometimes with yellowish scales underneath. Viewed from below, on a closed-cap specimen, the twin-layered ring has a well-developed "cogwheel" pattern around the stipe. This is the lower part of the double ring. The stalk is 5–12 cm (2–4+1⁄2 in) long and 1–3 cm wide.
The spores are brown and smooth, producing a dark brown spore print.
Begin with the source’s own compact description: “Agaricus arvensis” is species of fungus. The dossier treats that line as a proposition to test through Agaricus, arvensis and species, not as a finished interpretation.
Why this record matters
The phrase “species of fungus” supplies a clear boundary for inquiry. It also exposes the unanswered questions: who defined that boundary, when it became stable and which sources sit outside it.
The date and method of observation matter as much as the stated conclusion, especially where classification or consensus has changed. The source revision retrieved here is dated Aug 29, 2026. The linked authority identifier is Q690801. None of the 0 selected statements returned an explicit reference. The first chronological checks are 1774.
A general summary may omit uncertainty, sample limits or methodological disagreement that is explicit in the technical record. The lead is largely declarative, so disagreement and counter-evidence require a deliberate search beyond the opening account. Authority statements aid reconciliation but still require their own references, qualifiers and ranks to be checked.
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This entry incorporates text from “Agaricus arvensis” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.