Ganoderma, a genus of polypore fungi in the family Ganodermataceae, includes about 80 species, many from tropical regions. Because of their genetic diversity, use in traditional Asian medicines, and potential in bioremediation, they are an important genus economically. Ganoderma can be differentiated from other polypores because they have a double-walled basidiospore. They are sometimes called shelf mushrooms or bracket fungi.
The genus Ganoderma was established as a genus in 1881 by Karsten and included only one species, G. lucidum (Curtis) Karst . Previously, this taxon was characterized as Boletus lucidus Curtis (1781) and then Polyporus lucidus (Curtis) Fr. (1821) (Karsten 1881). The species P. lucidus was characterized by having a laccate (shiny or polished) pileus and stipe, and this is a character that Murrill suspected was the reason for Karsten’s division because only one species was included, G. lucidum . Patouillard revised Karsten’s genus Ganoderma to include all species with pigmented spores, adhering tubes and laccate crusted pilei, which resulted with a total of 48 species classified under the genus Ganoderma in his 1889 monograph. Until Murrill investigated Ganoderma in North America in 1902, previous work had focused solely on European species including, for example, G. lucidum, G. resinaceum Boud. (1890) and G. valesiacum Boud. (1895).
Ganoderma are characterized by basidiocarps that are large, perennial, woody brackets also called "conks". They are lignicolous and leathery either with or without a stem. The fruit bodies typically grow in a fan-like or hoof-like form on the trunks of living or dead trees. They have double-walled, truncate spores with yellow to brown ornamented inner layers.
The genus was named by Karsten in 1881. Members of the family Ganodermataceae were traditionally considered difficult to classify because of the lack of reliable morphological characteristics, the overabundance of synonyms, and the widespread misuse of names. Until recently, the genus was divided into two sections – Section Ganoderma with a shiny cap surface (like Ganoderma lucidum) and Elfvingia, with a dull cap surface, like Ganoderma applanatum.
Phylogenetic analysis using DNA sequence information have helped to clarify our understanding of the relationships amongst Ganoderma species. The genus may now be divided into six monophyletic groups:
- G. colossus group
- G. applanatum group
- G. tsugae group
- Asian G. lucidum group
- G. meredithiae group
- G. resinaceum group
With the rise of molecular phylogenies in the late 20th century, species concept hypotheses were tested to determine the relatedness amongst the nuanced morphological variabilities of the laccate Ganoderma taxa. In 1995, Moncalvo et al constructed a phylogeny of the rDNA, which was the universally accepted locus at that time, and found five major clades of the laccate species amongst the 29 isolates tested. It turned out that G. lucidum was not a monophyletic species, and further work needed to be done to clarify this taxonomic problem. They also found that G. resinaceum from Europe, and the North American ‘G. lucdium’, which Adaskaveg and Gilbertson found to be biologically compatible in vitro, did not cluster together. Moncalvo et al. reject biological species complexes as a sole tool to distinguish a taxon, and suggested using a combination between biological and phylogenetic species concepts to define unique Ganoderma taxa.
In 1905, American mycologist William Murrill delineated the genus Tomophagus to accommodate the single species G. colossus (then known as Polyporus colossus) which had distinctive morphological features that did not fit in with the other species. Historically, however, Tomophagus has generally been regarded as a synonym for Ganoderma. Nearly a century later, phylogenetic analyses vindicated Murrill's original placement, as it has shown to be a taxonomically distinct appropriate genus.
Some Ganoderma species can cause major long-term crop losses, especially with trees:
- G. orbiforme (= G. boninense), G. zonatum and G. miniatocinctum are responsible for basal stem rot disease in Asian oil palm plantations.
- G. philippii and G. pseudoferreum - Responsible for the root rot of cacao, coffee, rubber and tea trees.
Ganoderma are wood-decaying fungi with a cosmopolitan distribution. They can grow on both coniferous and hardwood species. They are white-rot fungi with enzymes that allow them to break down wood components, such as lignin and cellulose. There has been significant research interest on the wood-degrading enzymes of Ganoderma species for industrial applications, such as biopulping. or bioremediation.
For centuries, Ganoderma species have been used in traditional medicine in many parts of Asia. These species are often mislabeled as 'G. lucidum', although genetic testing has shown this to be multiple species such as G. lingzhi, G. multipileum, and G. sichuanense . Several species of Ganoderma contain diverse phytochemicals with undefined properties in vivo, such as triterpenoids and polysaccharides, an area of investigation under basic research.
Although various Ganoderma species are used in folk medicine for supposed benefits and have been investigated for their potential effects in humans, there is no evidence from high-quality clinical research that Ganoderma phytochemicals have any effect in humans, such as in cancer research.
Other notable species
- Ganoderma applanatum - Also known as the Artist's conk. An infestation of this species was the main factor in the loss of the Anne Frank Tree.
- Ganoderma lucidum - Also known as Reishi or Lingzhi.
- Ganoderma multipileum
- Ganoderma tsugae - A polypore which grows on conifers, especially hemlock, giving it its common name, Hemlock varnish shelf. Similar in appearance to Ganoderma lucidum, which typically grows on hardwoods.
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