Clitocybe acromelalga is a basidiomycete fungus

Fungus

A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...

 of the large genus Clitocybe

Clitocybe

Hundreds of species of mushrooms compose the fungus genus Clitocybe. They are characterized by white, off-white, buff, cream, pink, or light-yellow spores, gills running down the stem, and pale white to brown or lilac coloration. They are primarily saprotrophic, decomposing forest ground litter...

 found in Japan. It was discovered to be poisonous in 1918, when symptoms of occurred within 3 days of consumption. It had been mistaken for the edible blewit Lepista inversa.

Consumption of a related species, C. amoenolens

Clitocybe amoenolens

Clitocybe amoenolens, commonly known as the paralysis funnel, is an agaric fungus of the large genus Clitocybe. It was originally described from Morocco in 1975 by the French mycologist Malençon. It was discovered to be poisonous after several people had consumed specimens all found in the alpine...

from France has resulted in the same condition.