Tricholoma pessundatum

Tricholoma pessundatum is a mushroom of the agaric genus "Tricholoma". First described as "Agaricus pessundatus" by Elias Magnus Fries in 1821, it was transferred to the genus "Tricholoma" by Lucien Quélet in 1872.
The species has as sour meal odor, and contains toxins which can cause severe gastrointestinal upset.