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Polypores, also called bracket or shelf fungi, are a morphological group of basidiomycete-like gilled mushrooms and hydnoid fungi that form large fruiting bodies called conks, which are typically woody, circular, shelf- or bracket-shaped, with pores or tubes on the underside.
Conks lie in a close planar grouping of separate or interconnected horizontal rows. Brackets can range from only a single row of a few caps, to dozens of rows of caps that can weigh several hundred pounds. They are mainly found on (living and dead) and coarse woody debris, and may resemble . Some form annual fruiting bodies while others are perennial and grow larger year after year. Bracket fungi are typically tough and sturdy and produce their spores, called , within the pores that typically make up the undersurface.
Most polypores inhabit tree trunks or branches consuming the wood, but some soil-inhabiting species form mycorrhiza with trees. Polypores and the related corticioid fungi are the most important agents of wood decay, playing a very significant role in nutrient cycling and aiding carbon dioxide absorption by forest ecosystems. Several polypore species are serious pathogens of plantation trees and are major causes of timber spoilage.
As polypores are much more diverse in old natural forests with abundant dead wood than in younger managed forests or plantations, a number of species have declined drastically and are under threat of extinction due to logging and deforestation. Polypores are used in traditional medicine, and they are actively studied for various industrial applications.
The Polyporales in the modern sense are not only polypores but also other fruiting body types such as Corticioid fungi, hydnoid fungi and agaricoid mushrooms.
Currently polypores are divided into about 170 genera.Ryvarden L (1990) Genera of polypores. Fungiflora, Oslo.
Forms of polypore fruit bodies range from mushroom-shaped to thin effused patches (corticioid fungi) that develop on dead wood. Perennial fruit bodies of some species growing on living trees can grow over 80 years old (e.g. Phellinus igniarius). Most species of polypores develop new, short-lived fruit bodies annually or several times every year. Abundant fruit takes place during the autumn or rainy season.
Structure of the fruit bodies is simple. Effused or resupinate fruit bodies typically consist of two layers - a tube layer of vertically arranged tubes that open downwards, and supporting layer called subiculum that supports and attached the tubes to substrate. In fruit bodies with a cap (pileate fruit bodies) the tissue between upper surface and the pore layer is called context. A few polypores (e.g. Fomes fomentarius and Inocutis rhaedes) also have a core between context and substrate. A minority of polypores also have a stalk (stipe) that attach to the cap either laterally or centrally depending on the species.
Polypore tubes are a honeycomb-like structure, where the individual tubes have fused together. Their sides are covered with a spore-forming surface, the hymenium. The tubes offer shelter for developing spores and help to increase the area of the spore-producing surface. Pore size and shape vary a lot between species, but little within a species – some Hexagonia spp. have 5 mm wide pores whereas pores of Antrodiella spp. are invisible to naked eye with 15 pores per mm. Generally the larger the pores, the larger the spores. A few polypores produce asexual spores ( or conidia) in the upper surface of their cap (e.g. Echinopora aculeifera, Oligoporus ptychogaster) or without the presence of a sexual fruit body (e.g. Inonotus rickii, Heterobasidion spp.).Gilbertson RL, Ryvarden L (1986) North American polypores 1, Abortiporus to Lindtneria. Oslo, Fungiflora.
Bolete mushrooms are a separate morphological group not included in polypores even though they have tubes. Fleshy fruiting bodies with a stalk and microscopic characters separate boletes from polypores.
Most brown-rot fungi are polypores. Most of these species have lost their lignin degradation ability through evolution but are very efficient in degrading cellulose. Brown-rot fungi are prevalent on conifer hosts and open, sun-exposed habitats. The fungal community in any single trunk may include both white-rot and brown-rot species, complementing each other's wood degradation strategies.
Polypores and other decomposer fungi are the first step in food chains that feed on decomposed plant material. A rich fauna of insects, mites and other invertebrates feed on polypore mycelium and fruiting bodies, further providing food for birds and other larger animals. Woodpeckers and other hole nesting birds typically carve their nests in softer wood decomposed by polypores.
Polypores can decline for many reasons. They can be dependent on a single host or a very special habitat. For instance Echinodontium ballouii has been found only in Atlantic white cedar swamps in the Northeastern USA.Gilbertson RL, Ryvarden L (1986) North American polypores 1, Abortiporus to Lindtneria. Oslo, Fungiflora. Species can be dependent on very old tree individuals like Bridgeoporus nobilissimus of the Northwestern USA. Both of these species also have a rather restricted range, making them more vulnerable to extinction.
In addition to the host tree individual, the characteristics of the surrounding habitat also matter. Some species prefer closed-canopy forest with a moist, even microclimate that could be disturbed for instance by logging (e.g. Skeletocutis jelicii). Others suffer from lack of open forest-fire habitat in areas where fire suppression is done (e.g. Gloeophyllum carbonarium in Nordic countries where forest fires are part of the natural forest dynamics).
For most declining species the main problem is lack of dead wood in the forest. When suitable tree trunks are too sparse in the landscape, not all species are able to spread to new trunks after old ones have been consumed, causing the population to decline and eventually vanish. Thus, species that are abundant in old-growth forests with abundant dead wood can be totally absent from managed forests. For instance Amylocystis lapponica and Fomitopsis rosea are dominant species in North European old-growth spruce forests from Poland to Norway, but absent in managed forests.
Climate change may cause a problem for polypores that are already dependent on a few fragments of old-growth forests and may be unable to migrate with changing vegetation.
The first indicator list of polypores widely used in forest inventories and conservation work was developed in northern Sweden in 1992 ("Steget före" method).Karström M (1992) Steget före – en presentation. Svensk Botanisk Tidskrift 86: 103-114. "Steget före" list included six polypores in three value classes. In Finland, a list of 30 species for spruce-dominated forests was published in 1993 and widely adopted.Kotiranta H, Niemelä T (1996) Uhanalaiset käävät Suomessa. 2nd ed. Suomen ympäristökeskus, Helsinki. Later a similar list for pine-dominated forests was published. Longer lists of indicator species have since been published in Sweden.Nitare J (2000) Signalarter. Indikatorer på skyddsvärd skog. Flora över kryptogamer. Skogsstyrelsen förlag, Jönköping.
Many indicator species are red list, but not necessarily all. National red lists of fungi typically include many polypores and are used as indicator lists of conservation value in many European countries.
The tinder fungus ( Fomes fomentarius) has been used as tinder since at least the time of Ötzi the Iceman. It has also been used to make a material similar to leather.
Ganoderma applanatum, the artist's conk, is used as a substrate for drawings. Fresh specimens develop dark brown lines when drawn upon with a stylus. The lines become permanent when the specimen is dried.
Polypores used in traditional medicine are Lingzhi mushroom (reishi or lingzhi), Trametes versicolor (turkey tail) and Ganoderma applanatum.
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