Russula subnigricans

Russula subnigricans, known as nisekurohatsu (Japanese), is a basidiomycete mushroom of the genus "Russula" found in China, Japan, and Taiwan.
Description.
The flesh turns pale red when cut, but doesn't turn black unlike "Russula nigricans".
The species was named by Japanese mycologist Tsuguo Hongo in 1955.
The name was formerly applied to the North American fungus "Russula eccentrica" in California. It has been reclassified as "Russula cantharellicola", where it grows in association with coast live oak ("Quercus agrifolia") trees in California oak woodland habitats.
Toxicity.
"Russula subnigricans" is a poisonous mushroom, and has been responsible for mushroom poisoning in Taiwan and Japan. The effect is a serious one, rhabdomyolysis.
The toxins responsible are the very unusual cycloprop-2-ene carboxylic acid (a toxic molecule consisting of only four carbon atoms) and Russuphelin A (a heavily chlorinated polyphenolic).