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Agaricus xanthodermus
General Details, Taxonomy and Biology, Clinical Effects, First Aid
Agaricus xanthodermus ( Yellow stainer )  [ Original photo copyright © David Catcheside ]
Phylum: Basidiomycota
Class: Basidiomycetes
Order: Agaricales
Family: Agaricaceae
Genus: Agaricus
Species: xanthodermus
Clinical Group: GROUP 5 - Gastrointestinal irritant mushroom poisoning
Common Names: Yellow stainer, Yellow staining mushroom
Gregarious and form large fairy rings. Found in deciduous forests on calcareous soil, occasionally in meadows and gardens. Also reported from light coniferous forests with calcareous soil.
PILEUS (cap) 5-12 cm in diameter, when very young closed and glandiform, then hemispherical, expanding to nearly plane. Margin in-rolled, in-curved, then convex to expanded, sometimes with a depressed center and a straight to reflexed marginal zone. White, with a faint brown tinge, on bruising or rubbing becomes yellow then fade in to dirty brown. Surface smooth to appressed white fibrillose, sometimes longitudinally fissured. Apex of young specimens could be punctate, older specimens may have erect, coarse re-curved scales.

LAMELLAE free with intercalated lamellulae and crowded. When young whitish, then dark brown to blackish brown. Edges eroded, with scattered whitish wooly filaments.

STIPE 6-10 cm in height and 1.2-1.5 cm thick. Equal, often with a small basal bulb and the bulb of younger specimens contain a short root like appendage. Surface of the stipe white, becoming yellow with rubbing, then brown. Longitudinally striate and sometimes the part above the annulus is covered with hairy scales.

ANNULUS found on the upper third of the stipe, fairly thick, can be removed upward, upper surface ribbed and covered with fine soft hairs, incurved marginal zone comprises of two to three layers and the lowest maybe split.

FLESH white, some areas yellow, specially the base of the stipe. In the pileus the marginal zone is very thin, becoming about 1 cm thick towards the centre. In the stipe hollow, when young filled with silky filaments.

SPORE PRINT is purple brown

Spores 5-7 x 3-4 μm, ellipsoidal to ovoid, smooth, pale brownish.
Basidia 4 spored, 20-28 x 6-7 μm.
Cheilocystidia oval balloon shaped, small, 10-20 x 8-14 μm.
First Aid
Description: First aid for poisoning by plants or mushrooms where no agreed first aid method is currently available.
In the absence of research or clinical data about first aid for poisoning caused by this species, no first aid method can currently be recommended. Seek Medical Advice without delay.
Clinical Effects & Treatment
Clinical Classification
Group 5 - Gastrointestinal irritant mushroom poisoning
A phenol has been isolated. Yellow colouration on rubbing the fungus is due to the formation of 4, 4'-dihydroxyazo-benzene. Aparicone, xanthodermin and 4-hydroxy-benzene-diazonium ion have been isolated.

This mushroom contains p-hydroxyaniline and 90 ppm of the yellow pigment p-azophenol. The p,p'-dihydroxybiphenyl is a product of the diazonium ion.

Toxic heavy metals
The yellow stainer has the ability to accumulate cadmium, and could contain 50 parts per million. Phosphoglyco protein is thought to be responsible for this action.
This fungus also has the ability to accumulate mercury.

Cadmium and arsenic accumulations have been found in these species.

Clinical Effects Overview
A wide variety of mushrooms can induce gastrointestinal irritation when ingested. Such GIT effects are the most common type of mushroom poisoning. The clinical presentation may differ between groups. The following is an overview of this whole class of poisonous mushrooms, where diverse toxins are involved, but with similar clinical profiles.

Poisoning follows ingestion of either raw or cooked mushrooms, though cooking can reduce toxicity in some cases. Symptoms of GIT disturbance commence 1-3 hrs post-ingestion and can include vomiting, abdominal pain and diarrhoea. The diarrhoea may be profuse and may become bloody, especially after consumption of Chlorophyllum molybdites. GIT fluid loss can be severe and can cause secondary hypovolaemic shock, especially in children. Secondary problems are possible in this latter setting, such as DIC and renal failure and fatalities have occurred, notably in children. However, for most patients, this is an unpleasant but self-limited illness, with resolution of symptoms after 3-4 hrs in many cases. A few species cause longer lasting effects, taking up to 48 hrs to resolve in some cases.

Apart from the risk of massive GIT fluid loss and its complications, the major risk relates to unsuspected co-ingestion of more toxic species, such as amatoxic mushrooms.
Primary Clinical Effect
The primary effect is short-lived gastrointestinal irritation.
Treatment Overview
Most cases of gastrointestinal irritant mushroom ingestion will develop a self limited illness and recover over a period of hours, with no more than simple supportive care, notably fluid replacement.

Only a minority of cases will have severe GIT fluid loss requiring full resuscitation with IV fluids and, on occasion, pressors. A further small subset will develop hypovolaemic shock and complications thereof, requiring more substantial intervention.

The major risk is undocumented co-ingestion of more toxic mushrooms, such as amatoxic species.
Agaricus xanthodermus ( Yellow stainer ) [ Original photo copyright © David Catcheside ]
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Agaricus xanthodermus ( Yellow stainer ) [ Original photo copyright © Pam Catcheside ]
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Agaricus xanthodermus ( Yellow stainer ) [ Original photo copyright © Jens V Petersen ]
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Agaricus xanthodermus ( Yellow stainer ) [ Original photo copyright © Jens V Petersen ]
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