Monday, 13 December 2010

Ghost fungi - bioluminescence

Omphalotus nidiformis or 'ghost fungus' is a gilled basidiomycete mushroom found in southern Australia most notable for its bioluminescent properties. Generally found growing on dead or dying trees, it is saprotroph and parasite.

Its scientific name is derived from the Latin nidus "nest", hence 'nest shaped'. Similar in appearance to the oyster mushroom, it was previously considered a member of the same genus, Pleurotus, and described under the former names Pleurotus nidiformis or Pleurotus lampas. However, it is poisonous and while not lethal, consuming this mushroom leads to severe cramps and vomiting. Poisonings have occurred over confusion with oyster mushrooms. It is one of several species with bioluminescent properties occurring worldwide, all of which are poisonous with the exception of Armillaria.

The ghost fungus was initially described in 1844 by English naturalist Miles Joseph Berkeley as Agaricus nidiformis, before being later placed in the genus Pleurotus in 1887. It was finally placed in the genus Omphalotus with other bioluminescent mushrooms by Orson K. Miller, Jr. in 1994.[1] Material had been collected by James Drummond in 1841 from the Swan River and described by Berkeley as both this and Agaricus lampas. The latter name (as Pleurotus lampas) persisted in some texts but has been synonymised with this species. Its specific epithet is derived from the Latin terms nīdus 'nest' and forma 'shape' or 'form', hence 'nest shaped'.[2] Lampas is derived from the Greek lampas/λαμπας 'torch'.[3] Drummond reported that the local aborigines were fearful when shown the luminescent fungus and called out chinga, a local word for spirit.[4]

Several species with similar bioluminescent properties occur worldwide, all of which are poisonous. The best known are the North American jack o'lantern mushroom (Omphalotus olearius) and the Tsukiyotake (Omphalotus japonicus (Kawam.) Kirchm. & O.K. Mill., aka Lampteromyces japonicus (Kawam.) Sing.) found in Japan and eastern Asia. A recent molecular study shows the ghost fungus to be most closely related to the western jack o'lantern mushroom (Omphalotus olivascens) which is abundant in Southern and Central California.

The fruiting body of the ghost fungus can be found on dead or diseased wood, where it causes white heart rot.[6] A saprobe or parasite, it is nonspecific in its needs and can be found on native Banksia, Hakea or Acacia and various Myrtaceae as well as introduced trees such as Pinus or Platanus species.[7] They may be first seen at night as a pale whitish glow at the base of trees in a eucalypt forest.[8]

The cap is very variable in colour, ranging from cream though often tinted with orange, brownish, greyish, purple or even bluish-black shades. Younger specimens are often darker. Growing up to 30 cm (12 in) in diameter it is funnel-shaped or fan-shaped in appearance with inrolled margins. The cream-white gills are decurrent and often drip with moisture. The stipe may be central to lateral in its attachment to the cap and is up to 8 cm (3 in) long and tapers to the base. The thin flesh is creamy white in colour. There is no distinctive smell or taste. The spore print is white.[9]

O. nidiformis' bioluminescent gillsIts bioluminescence is best seen in low-light conditions when the viewer's eyes develop night vision. The gills are the most luminescent part of the fungus, emitting a greenish light which fades with age. The light has been reported bright enough to read a watch face by.[8]

It may be confused with the brown oyster mushroom (Pleurotus australis), which is brown in colour and does not glow in the dark.[9]

It occurs in south western Western Australia, where it was first recorded by Scottish naturalist James Drummond,[7] and south eastern Australia, from eastern South Australia through to southeast Queensland. It also occurs in Tasmania.[9] It can be found in eucalypt and pine forests,[10] as well as in urban parks and gardens. Fruiting bodies can be numerous and occur in overlapping clusters on dead wood

Omphalotus nidiformis is not edible. Although reputedly mild tasting,[7] eating it will result in vomiting which generally occurs 30 minutes to two hours after consumption and lasts for several hours. There is no diarrhea and patients recover without lasting ill-effects.[11] The toxic ingredient is thought to be a sesquiterpene compound known as illudin, which is also responsible for its bioluminescence

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