Russula subnigricans is a basidiomycete mushroom

Mushroom

A mushroom is the fleshy, spore-bearing fruiting body of a fungus, typically produced above ground on soil or on its food source. The standard for the name "mushroom" is the cultivated white button mushroom, Agaricus bisporus; hence the word "mushroom" is most often applied to those fungi that...

 of the genus Russula

Russula

Around 750 worldwide species of mycorrhizal mushrooms compose the genus Russula. They are typically common, fairly large, and brightly colored - making them one of the most recognizable genera among mycologists and mushroom collectors...

found in China and North America. It has been responsible for mushroom poisoning in Taiwan. The effect was a serious one, rhabdomyolysis

Rhabdomyolysis

Rhabdomyolysis is a condition in which damaged skeletal muscle tissue breaks down rapidly. Breakdown products of damaged muscle cells are released into the bloodstream; some of these, such as the protein myoglobin, are harmful to the kidneys and may lead to kidney failure...

. Several active agents have been isolated; one designated russuphelin A by researchers in Japan.

The species was named by Japanese mycologist Tsuguo Hongo

Tsuguo Hongo

was a Japanese mycologist who specialized in the biogeography and taxonomy of Agaricales.Hongo entered the Department of Biology at what is now Hiroshima University in 1943, where he studied botany until graduating in 1946 with a B.Sc....

 in 1955. The name has also been applied to a North American fungus Russula eccentrica.

The toxin has been identified as cycloprop-2-ene carboxylic acid

Cycloprop-2-ene carboxylic acid

Cycloprop-2-ene carboxylic acid is a toxic molecule found in some mushrooms such as Russula subnigricans and Tricholoma equestre.When ingested, the molecule is known to cause rhabdomyolysis....

and has only four carbon atoms.