Omphalotus nidiformis, or ghost fungus, is a gilled basidiomycete mushroom most notable for its bioluminescent properties. It is known to be found primarily in southern Australia and Tasmania, but was reported from India in 2012 and 2018. The fan or funnel shaped fruit bodies are up to 30 cm (12 in) across, with cream-coloured caps overlain with shades of orange, brown, purple, or bluish-black. The white or cream gills run down the length of the stipe, which is up to 8 cm (3 in) long and tapers in thickness to the base. The fungus is both saprotrophic and parasitic, and its fruit bodies are generally found growing in overlapping clusters on a wide variety of dead or dying trees. First described scientifically in 1844, the fungus has been known by several names in its taxonomic history. It was assigned its current name by Orson K. Miller, Jr. in 1994. Its epithet name is derived from the Latin nidus "nest", hence 'nest shaped'. Similar in appearance to the common edible oyster mushroom, it was previously considered a member of the same genus, Pleurotus, and described under the former names Pleurotus nidiformis or Pleurotus lampas. Unlike oyster mushrooms, O. nidiformis is poisonous; while not lethal, its consumption leads to severe cramps and vomiting. The toxic properties of the mushroom are attributed to compounds called illudins.
Taxonomy and naming The ghost fungus was initially described in 1844 by English naturalist Miles Joseph Berkeley as Agaricus nidiformis. Berkeley felt it was related to Agaricus ostreatus (now Pleurotus ostreatus) but remarked it was a "far more magnificent species". Material was originally collected by Scottish naturalist James Drummond in 1841 on Banksia wood along the Swan River. He wrote "when this fungus was laid on a newspaper, it emitted by night a phosphorescent light, enabling us to read the words around it; and it continued to do so for several nights with gradually decreasing intensity as the plant dried up." More material collected from near the base of a "sickly but living" shrub (Grevillea drummondii) was named as Agaricus lampas by Berkeley. He noted both were phosphorescent and closely related species. Tasmanian botanist Ronald Campbell Gunn collected material in October 1845 from that state, which Berkeley felt differed from previous collections in having more demarcated and less decurrent gills and a shorter stipe, and named it Agaricus phosphorus in 1848. Italian mycologist Pier Andrea Saccardo placed all three named taxa in the genus Pleurotus in 1887. These names have been synonymised with O. nidiformis, although the name Pleurotus lampas persisted in some texts, including the 1934–35 monograph of Australian fungi by John Burton Cleland. In reviewing the published literature, Victorian botanical liaison officer Jim Willis was aware of Rolf Singer's placing of Pleurotus olearius into the genus Omphalotus, but stopped short of transferring the ghost fungus across, even though he conceded it was wrongly placed in Pleurotus. Investigating the species in 1994, Orson K. Miller, Jr. gave the ghost fungus its current binomial name when he transferred it to the genus Omphalotus with other bioluminescent mushrooms. The specific epithet nidiformis is derived from the Latin terms nīdus 'nest' and forma 'shape' or 'form', hence 'nest shaped'. Lampas is derived from the Greek lampas/λαμπας 'torch'. Common names include ghost fungus and Australian glow fungus. Drummond reported that the local Aboriginal people were fearful when shown the luminescent fungus and called out chinga, a local word for spirit; Drummond himself likened it to a will-o'-the-wisp. On the Springbrook Plateau in southeastern Queensland, the local Kombumerri people believed the lights to be ancestors and gave the area a wide berth out of respect.
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. A 2004 molecular study shows the ghost fungus to be most closely related to the western jack o'lantern mushroom (O. olivascens), which is abundant in Southern and Central California. Miller notes that the colours and shades of the ghost fungus most closely resemble this species. Laboratory breeding experiments with it and other Omphalotus species have revealed a low level of compatibility (ability to breed and produce fertile hybrids), suggesting it is genetically distinct and has been isolated for a long time. It is particularly poorly compatible with O. illudens, the authors of the study suggesting the separation may have been as long ago as the Late Carboniferous separation of Gondwana from Laurasia but conceding the lack of any fossil record makes it impossible to know whether the genus even existed at the time.
Variation Miller noted there appeared to be two colour forms reported across its range, namely a more cream-coloured form with darker shades of brown and grey in its cap that darkens with age, and a more wholly brownish form with paler edges and darker centre to its cap. He found the cream-coloured form to be strongly luminescent—the brightest of any fungus in the genus—with the cap, stipe and gills all glowing. The brown form was generally fainter, with its luminescence restricted to the gills. However, some strongly luminescent wholly brown-coloured mushrooms were recorded, and laboratory experiments showed all interbred freely and produced fertile offspring, leading Miller to conclude that these were phenotypic variants of a single taxon.
Description
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