''Agaricus xanthodermus'', commonly known as the yellow-staining agaricus, yellow-staining mushroom or yellow-stainer, is a species of fungus in the genus ''

Agaricus ''Agaricus'' is a genus of mushroom-forming fungi containing both edible and poisonous species, with over 400 members worldwide and possibly again as many disputed or newly discovered species. The genus includes the common ("button") mushroom ...

''. It displays a strong yellow colouration at the base of the stem when cut. It has a phenolic smell. It is poisonous for most people, causing gastric upset, but can be eaten by some without apparent negative effect.

Taxonomy

This species was first officially defined under the name ''Agaricus xanthodermus'' in 1876 by Léon Gaston Genevier, in a letter published in the bulletin of the French Botanical Society. Genevier described the ''

'' mushrooms commonly eaten (perhaps sometimes inadvisedly) in the region of

Nantes Nantes (, ; ; or ; ) is a city in the Loire-Atlantique department of France on the Loire, from the Atlantic Ocean, Atlantic coast. The city is the List of communes in France with over 20,000 inhabitants, sixth largest in France, with a pop ...

, and attempted to clarify the distinctions between them. He proposed a detailed reclassification into 5 species, including this new one. Apparently up until that time, these yellow-staining mushrooms were considered to be just varieties of other edible species: ''A. edulis'', '' A. arvensis'', and '' A. silvicola''. The epithet ''xanthodermus'' is derived from the

Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...

words for "yellow" and "skin", which were then given a Latin adjective ending. This is the official name, but the form ''Agaricus xanthoderma'' is also often seen. In the latter name, ''-derma'' "skin" is a neuter noun which does not have to agree in gender with ''Agaricus'', and so this form is legal according to the rules of botanical nomenclature.

Description

The

cap A cap is a flat headgear, usually with a visor. Caps have crowns that fit very close to the head. They made their first appearance as early as 3200 BC. The origin of the word "cap" comes from the Old French word "chapeau" which means "head co ...

ranges from in diameter. It is initially convex, with some young specimens having a squarish shape, though flattening with age. It is whitish, with light brown tints towards the centre. The cap is dry and smooth, but can be scaly when old. The

gills A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are ...

of this mushroom progress from pale-pink to a chocolate color. Its white stipe measures tall and 1–3 wide, and is bulbous with a skirt-like ring. Microscopically, the cheilocystidia are club-shaped. The

spores In biology, a spore is a unit of sexual (in fungi) or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plant ...

are brown, elliptical, and smooth, measuring 6–7 × 3–4 μm. The specieshas an unpleasant characteristic smell, which is phenolic, reminiscent of ink or carbolic soap. The smell is especially strong at the base of the stem. On cooking, the smell becomes very noticeable, and this may deter people from eating it inadvertently.

Similar species

The main identifying feature is an immediate bright yellow colouration on cutting through the base of the stem, or scraping the flesh; later, the affected area fades to a dull brown. Numerous edible ''Agaricus'' species, such as '' A. augustus'', '' A. arvensis'' and '' A. silvicola'', turn yellow to a greater or lesser extent, but they do not display such an intense reaction. ''Agaricus xanthodermus'' belongs to a group of related species (the "Xanthodermati") which likewise discolour bright yellow and have a

phenol Phenol (also known as carbolic acid, phenolic acid, or benzenol) is an aromatic organic compound with the molecular formula . It is a white crystalline solid that is volatile and can catch fire. The molecule consists of a phenyl group () ...

ic smell. They include ''A. praeclaresquamosus'' (formerly '' A. placomyces'') which has dark grey scales, '' A. moelleri'', and '' A. pilatianus'', which does not have a bulbous stem. '' Agaricus californicus'' is also similar in appearance. 2011-10-13 Agaricus xanthodermus Genev 181971

2011-10-13 Agaricus xanthodermus Genev 181971

Distribution and habitat

This mushroom is very common and widely distributed in North America, Europe, West Asia including eastern

Anatolia Anatolia (), also known as Asia Minor, is a peninsula in West Asia that makes up the majority of the land area of Turkey. It is the westernmost protrusion of Asia and is geographically bounded by the Mediterranean Sea to the south, the Aegean ...

and Iran, North Africa, and

southern Africa Southern Africa is the southernmost region of Africa. No definition is agreed upon, but some groupings include the United Nations geoscheme for Africa, United Nations geoscheme, the intergovernmental Southern African Development Community, and ...

. It has been introduced into

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

. It occurs in woods, lawns, gardens and hedgerows in autumn. This is a saprobic species. Karbol-Champignion2

Toxicity

Although it appears that some people can eat this mushroom without ill effects, it contains toxins which can cause serious gastrointestinal upset. It is indigestible and gives rise to symptoms of sweating, flushing, and severe stomach cramps. Of those who gather ''Agaricus''-style mushrooms, about 50% of the cases of poisoning are from this species.

References

External links

* * {{Taxonbar, from=Q1349044 xanthodermus Fungi described in 1876 Fungi of Europe Fungi of North America Poisonous fungi Fungus species