Omphalotus olivascens
Omphalotus olivascens, commonly known as the western jack-o'-lantern mushroom, is an orange to brown-colored gilled mushroom native to California and Mexico. Taxonomy. The fungus was described as new to science in 1976 by American mycologists Howard E. Bigelow, Orson K. Miller Jr., and Harry D. Thiers. A subspecies with blue flesh, "O. olivascens" var. "indigo", was described growing on live oak in Baja California, Mexico. Description. To an untrained eye, "O. olivascens" appears similar to some chanterelles, but unlike the chanterelle, the jack-o'-lantern mushroom has true, blade-like gills (rather than ridges) and it can  have olive coloration that chanterelles lack; also, "Omphalotus" species are saprotrophic, grow directly on wood, and are bioluminescent. The cap is wide. The stalks are long and wide. The spores are white to pale yellow. Ecology. A saprobe or parasite, "O. nidiformis" is nonspecific in its needs and is compatible with a wide variety of hosts. "Omphalotus" species cause a white rot by breaking down lignin in their tree hosts. Biochemistry. The jack o'lantern mushroom is poisonous; while not lethal, consuming this mushroom leads to very severe cramps, vomiting, and diarrhea. The toxic ingredient of many species of "Omphalotus" is  a sesquiterpene compound known as illudin S. This, along with illudin M, have been identified in "O. nidiformis". The two illudins are common to the genus "Omphalotus" and not found in any other basidiomycete mushroom. Similar species. Several "Omphalotus" species with similar bioluminescent properties occur worldwide, all of which are presumed poisonous. The best known are the North American jack o'lantern mushroom ("O. olearius") and the "tsukiyotake" ("O. japonicus" (Kawam.) Kirchm. & O.K. Mill. (formerly known as "Lampteromyces japonicus" (Kawam.) Sing.), found in Japan and eastern Asia. Molecular analysis shows the jack-o'-Lantern to be most closely related to the ghost  fungus "Omphalotus nidiformis". Miller notes that the colours and shades of the ghost fungus most closely resemble this species. "Gymnopilus junonius" is another similar-looking species.