Common name: Yellow staining mushroom
Botanical name: Agaricus xanthodermus
Other common names: Yellow stainer
General description: The slender stem is white or yellowish, swollen and often hollow at the base, and usually with a membranous white or yellowish ring at the top. When attempting to identify this agaric, it is best to pick the whole fruiting body, stem intact, of mature, but not over-mature, individuals which still have a firm cap and stem. Rubbing the cup surface with your finger may generate a slight yellow reaction, but cutting through the stem at the very base, as you would if dicing a shallot, should illicit an immediate vivid chrome yellow reaction. This reaction becomes less intense with increasing maturity, and gradually fades to brown with time since cutting. The odour is strong (phenolic), unpleasant, similar to iodine or kerosene, and is more intense on cooking.
Symptoms: Symptoms can begin immediately or up to two hours after the meal, and may include intense nausea, vomiting, diarrhoea, and abdominal pains.
Toxicity category: 2
Warning: Seek urgent medical attention for any ingestion.