Botanical name: Agaricus moelleri
Common names: Inky Mushroom, Dark Scaled Mushroom,
Seasonality: June to October (UK)
Habitat: Northern, temperate woodlands and forests. Will appear sporadically throughout the growing season. Usually found in clusters. Favours fertile alkaline soils.
Identification: This agaricus has a strong smell of disinfectant associated with it, similar to Iodine or Indian Ink, hence the common name "Inky". This smell is absent in edible varieties of agaric. Another ready identifier is that when bruised or cut, the flesh turns or "stains" yellow, another feature not present in edible forms.
"The cap has a greyish-brown patch in the centre and cold grey-brown scaling on the surrounding off-white background. It is 5 to 9 centimetres (2.0 to 3.5 in) in diameter..."
Toxicity: Quite. Will cause extreme pain, extreme gastric cramping and pain as well as fever like symptoms.
Photo courtesy of Zonda Grattus via wiki.