(This paper originally appeared in McIlvainea 14 (2): 74-82, 2000.)�

The polypores are a fascinating group of fungi, although they are usually ignored by most mycophiles because of their typical inedibility, commonly small size, unfamiliar habitat and general obscurity. However, these fungi are very interesting from an ecological, microscopic, and biotechnological standpoint, and are well worth observing and learning to identify. With practice, a great many species can be learned just by their macroscopic features. An added bonus from a collecting viewpoint is that, unlike fleshy mushrooms, most of these fungi can be found even during dry weather or in the winter, since many are tough or perennial and many others produce basidiocarps only beneath the surface of logs lying on the forest floor, where it remains wet most of the year.�

Polypores (family Polyporaceae and similar fungi) can be easily distinguished from the other common poroid fungi, the boletes, by their typically hard exterior, their usual "non-mushroom" shape, and their usual growth on wood as wood decomposers. You probably know that most boletes fruit on the ground as mycorrhizal fungi, having mutualistic relationship with the roots of trees and other plants.. In addition, the pore layer of boletes can usually be easily peeled off from the flesh (context). A related group, the crust-like corticioid fungi (family Corticiaceae and similar fungi), are also wood-decay basidiomycetes, but they are typically non-poroid and may have a wide variety of hymenophore (spore bearing surface) configurations; most of them are "flat" without any recognizable topology, although some of them are toothed, folded and even poroid.�

The polypores and corticioid fungi are important in natural ecosystems as decomposers of wood, recycling the nutrients and minerals in the wood and releasing them over a long period of time--- sometimes several hundred years from a single large down tree--- where they can be used by other forest organisms. Many species can also act as mild to severe pathogens of living forest trees. In addition to their scientific and ecological interest, some of the species are highly regarded by mycophagists (e.g. Laetiporus sulphureus, the sulfur shelf or chicken of the woods, and Grifola frondosa, hen of the woods, sheepshead or maitake). Many polypores can be used as natural dyes for wool (e.g. Phaeolus schweinitzii and Hapalopilus nidulans). Several polypores are used in oriental herbal medicine, mostly in making tea-like extracts, including Ganoderma lucidum (reishi), Polyporus umbellatus, and Grifola frondosa (maitake). The polypore use that holds the most potential benefit for people is probably in biotechnology. In addition, some of these fungi are highly valued by biotechnologists because of their wood-degrading (and especially lignin-degrading) abilities. More on this later.�

It is important to be able to distinguish the genera and species because proper identification and knowledge of relationships between taxa is the key to further study of the ecological, pathological, genetic, physiological, and biotechnological aspects of these fungi. For example, if you know a particular species is valuable for biotechnology, you might want to check out a closely related species for further usefulness�

Polyporus was once a catch-all genus for "non-mushroom-shaped" fungi with pores, but now there are more than 100 genera of polypore fungi that have been described and are now accepted. Most of these belong in the family Polyporaceae, but 5-7 other families (such as Ganodermataceae, Albatrelllaceae, Bondarzewiaceae, Fistulinaceae, and Hymenochaetaceae) are also now represented. This paper will focus on the types of macroscopic and microscopic characters that may be used to identify polypores to genus and to species, the ecological niches occupied by these interesting fungi, and how they can be exploited for human use.�

Early mycologists based their species and generic delimitations mostly on gross features of fruiting structures. This was the system developed by Linneaus for plants and later by Elias Magnus Fries (1794-1878) for fungi. Mycologists often refer to Friesian characteristics or Friesian families; these are based on macromorphological characters such as those used by Fries, who, for example, classified every gill-bearing fungus into the genus Agaricus and every pored fungus into Boletus (then later into Boletus or Polyporus, based largely on the shape and hardness of the fruiting body). This certainly made genus identification easy, but this was a gross oversimplification. Moreover, the names were not particularly informative about anything but a single character of the fungus. Modern generic classification should convey a multitude of information about a fungus. These two single-character genera, Boletus or Polyporus, are now often accepted at the order level of classification as the Boletales and the Polyporales.�

As described below, modern genera of polypores are largely distinguished on the basis of microscopic characteristics. I highly recommend Gilbertson and Ryvarden�s (1986, 1987) two volume set called North American Polypores. These volumes contain excellent keys and thorough introductory materials. I will summarize some important features of polypore systematics in this paper.�

Figure 2. Brown rot (upper picture) and white rot (lower). See text for details.�

Characters important in the delimitation of polypore genera�

Nutritional niche. An important character at the genus level is the nutritional niche occupied by the fungus. Most polypores are wood decay fungi. There are two fundamentally different ways in which wood can be rotted. Wood is composed mostly of two substances: cellulose (white) and lignin (brown). Cellulose forms the primary wall of all plant cells. Many plants add a second wall of lignin inside the primary wall, especially in wood. Brown rot fungi can degrade only the white cellulose and leave the brown lignin behind. In their simplest form, white rot fungi degrade the lignin and leave the white cellulose behind. Things get more complicated with the so-called simultaneous white rotters�these fungi can degrade both cellulose and lignin, albeit at different rates. In any case, the lignin is used up first and the white color of the cellulose can be seen. Even if you�re color blind, you can feel the wood to understand the differences. Brown rot fungi degrade the primary walls and leave the secondary lignin walls behind. Thus brown rotted wood crumbles to dust between your fingers since there is no primary wall structure. White rot fungi leave the stringy cellulose of the primary walls behind. There are often "sister" genera in the polypores, with seemingly identical characters, except that one causes a white rot and one causes a brown rot. A good example of this is Tyromyces, which causes a white rot and Oligoporus, which causes a brown rot. This distinction is also used in the Agaricales, where, for example, Pleurotus causes a white rot and the closely related Hypsizygus causes a brown rot.�

If you�re thinking ahead you realize there are a couple potential biotechnology uses for these white rot fungi.�

�Biopulping: One of the biggest energy expenditures in paper-making comes from removal of the brown lignin from the wood so that only the white cellulose is left to make paper. Usually this is done with chemical bleaches that are often contaminated with dioxins. There are ecological problems with disposal of these chemical. What if paper companies could use the enzymes of a white rot fungus to remove the lignin? This could result in a savings of both energy and time and avoid pollutive wastes being dumped out of the mills. The ideal fungus for this endeavor would be fast growing, able to tolerate the high temperatures of composting, and leave the cellulose virtually untouched. This ideal fungus would have the exact characteristics of Phanerochaete chrysosporium, a corticioid fungus, or Ceriporiopsis subvermispora, a resupinate polypore. The fungus works very well on the laboratory bench, but, as with many industrial bioprocesses, there have been problems with scaling up the process to an industrial level. Compare this to using a recipe for making chipped beef on toast at home to feeding the troops with the same recipe in battle; it just doesn�t work as well.�

�Bioremediation: Some of the lignin-degrading enzymes of white rot fungi will also degrade some toxic wastes that have the same general chemical configuration, such as PCB's, PCP's and TNT. There is enormous potential to use these fungi to clean up even Superfund sites. Again, this works very well on a small scale, but there are many of the same problems in scaling up the process�

Although most polypores cause wood decay, several genera have members that are mycorrhizal, forming mutualistically beneficial relationships with the root of trees. This might include Bondarzewia, which is probably not very closely related to the other polypores, and almost certainly belongs in the Russulales with Russula and Lactarius. Bondarzewia species have ornamented amyloid spores and sphaerocysts just like Russula and Lactarius, and when young even have lacticifers that produce a milky latex, as does Lactarius. Another mycorrhizal genus is Albatrellus. One must be careful not to ascribe mycorrhizal status to any fungus fruiting on the ground. Many of these ground polypores are root rot fungi (such as Inonotus tomentosus, Laetiporus cincinnatus, and Grifola frondosa), and many others typically grow from buried pieces of wood (e.g. Polyporus radicatus and P. melanopus).�

Even within the general nutritional categories, many polypores are restricted in their host range. This character is usually more important at the species level rather than at the genus level The largest dichotomy lies in hardwood vs. conifer hosts. However, some are even more specific, especially Phellinus species, where the species are almost all host-specific�so it would be nearly impossible to determine which Phellinus species without knowing the host. Fomes fomentarius and Piptoporus betulinus are found almost exclusively on birch trees (Betula spp.). Bridgeoporus nobilissimus (properly pronounced bridge-uh-PORE-us, since it�s named after William "Bridge" Cooke who first described the species) is known only from noble fir (Abies procera) and pacific silver fir (Abies amabilis), both of which are restricted to the Pacific Northwest in the U.S.A. It is important to note the host tree when collecting. This can be difficult, especially when the bark has already fallen off the tree. On a practical level all you can do sometimes is note which other trees are in the area; chances are pretty good the host tree will be one of those. Note that some geographic restriction of a polypore may be a consequence of the geographic restriction of the host tree.�

Table 1. Summary of characteristics of some common or important genera of polypores�

Form of the fruiting body. Polypores can take various forms. They may be pileate, having a pileus or distinguishable cap. Some may be stipitate, having a stalk. Or they may be resupinate (effused), lying flat on the substrate. Some may be effused-reflexed, which mean they lie flat on a flat (i.e. parallel to the ground) substrate, but form shelves where the substrate surface is not parallel to the ground Some genera are consistent, with all its species having one of these forms. More often there are mixed forms within a single genus. This character is more important at the species level, although sometimes even a single species may not be consistent.�

Form of the hymenophore (spore bearing surface). Since many fungi can grow only in a narrow ecological niche, they must produce enormous numbers of spores so that by chance some of their wind-dispersed spores will land on the right substrate and survive. Not surprisingly, most polypores do actually have pores, small holes on the underside of the fruiting body that increase the surface area for bearing basidia with their spores. However some genera have enlarged pores that may be mazelike or gill-like. Some even become hydnoid, with downward pointing teeth or spines. Some genera are consistent within these groups (mostly with pores), but here are many genera that have two or three of these hymenophore configurations. This character is more important at the species level, but again, there are some species that are quite variable depending on genetics and on ecological conditions. The form may even change depending on which side of the substrate the fungus is fruiting, especially if the substrate suddenly changes to be perpendicular to the ground.�

<!--[if gte vml 1]> Figure 3. Kinds of hyphae of polypores. A. generative hyphae with clamps B. generative hyphae with no clamps, simple septa C. Skeletal hyphae D. Binding Hyphae�

Hyphal System. The major microscopic characteristic separating the genera is the type of hyphal system, which can be monomitic, dimitic, or trimitic. You have probably noticed that some polypores are very soft and last for only one season, while others are very hard and often perennial. This is usually a direct result of the hyphal type found within the polypore fruiting body.�

Monomitic species have only septate generative hyphae (Fig 3A and B), which are responsible for growth and transport of food and other materials through the fruiting body. These may be thin-walled or thick-walled, clamped (Fig. 3A) or unclamped (Fig. 3B). Most of these species have fruiting bodies that are soft. (e.g. Tyromyces chioneus, the cheese polypore, and Oligoporus caesius, the blue cheese polypore). Dimitic-skeletal species have septate generative hyphae + thick-walled non-septate skeletal hyphae (Fig. 3C), which provide the hard structure found in many polypores (e.g. Ganoderma applanatum, the artist�s conk). Dimitic-binding species have septate generative hyphae + thin often-branching binding hyphae (Fig 3D), which are responsible for holding the other hyphae together (e.g. Laetiporus sulphureus, the sulfur shelf or chicken-of-the-woods). Trimitic species have septate generative hyphae + thick-walled non-septate skeletal hyphae + thin often-branching binding hyphae. A good example of this is the turkey-tail, Trametes versicolor, as well as most other Trametes species.�

On a practical level it may be difficult to determine the hyphal system of a fungal fruiting structure. There may be intergradations between the groups, especially between dimitic and trimitic. The fungi don�t read the books the way we do, so they don�t know what they�re supposed to look like or that they�re supposed to fit into our easy categories. A good tip to follow is that the difference between monomitic and dimitic is analogous to the Grand Canyon, while the difference between dimitic and trimitic is just a ditch on the side of the road.�

Another microscopic character usually important at the genus level is the presence of simple septa vs. clamped septa on generative hyphae. Clamps (Fig. 3A) are appendages formed on the outside of the cylindrical hyphae that maintain the dikaryotic (2-nucleate) state in the hyphae. Simple septate species lack clamp connections (Fig. 3B), and it is not known how these species maintain their dikaryotic state. Often it is difficult to find generative hyphae in fruiting bodies, since many polypores, particularly perennials, are composed mostly of skeletal hyphae for protection. Usually you can find generative hyphae nearest the basidia, in the trama (flesh) of the pores. This makes sense, since the basidia need the nourishment coming from the mycelium in the wood. Often you will need to chop up the fruiting body to see the hyphae and the septa. One important note is that there are a few genera (e.g. Polyporus) that have members with either clamped or simple septa.�

Type of cystidia and their origin (if present). Cystidia are actually found in very few genera of polypores, but when present they are a diagnostic feature. Some things to look for are the shape, size, thickness, and any crystals that are found at or near the ends. One common polypore with cystidia is the purple parchment fungus, Trichaptum biforme. It has beautiful long cylindrical thick-walled cystidia, with medium sized crystals at the ends. These crystals are thought to be a result of excretion of waste products by the fungus. Cystidia may originate in the hymenium (the layer that contains basidia) or they may originate in the trama.�

Several spore characteristic are also important, including reaction in Melzer's solution. [e.g. amyloid spores in Wrightoporia, Bondarzewia, and Amylosporus; dextrinoid spores in Perenniporia]. There are actually very few genera that react in Melzer�s reagent compared with agarics. General spore size and shape are far more important characters. To cite but two examples, there are rounded small spores in Rigidoporus and generally cylindrical spores in Trametes. Unusual spore ornamentation may be important in distinguishing some genera. For example, the "double" wall of Ganoderma species is highly diagnostic�some polyporologists even place Ganoderma in a separate family, the Ganodermataceae, because of this unusual characteristic. Other diagnostic spore walls are the sculptured walls of Pachykytospora and the minutely echinulate spores in Heterobasidion.

Hymenochaetaceae. An even higher level of taxonomy is the separation of the two families Polyporaceae and Hymenochaetaceae. The family Hymenochaetaceae is a prime example of why hymenophore (spore bearing surface) configuration is not the best character to use in family delimitations. The members of this family all have the following microscopic characters in common: simple septa (no clamps), turn black in 3% KOH, may have thick walled setae or setal hyphae. Various hymenophore configurations are included in this family: smooth, Hymenochaete, and Stiptochaete, a stalked form; toothed, Hydnochaete; andporoid Phellinus (dimitic, usually perennial, wood decayer), Inonotus (monomitic, usually annual, wood decayer), or Coltricia (mycorrhizal).

Special characters. There are a number of unique, or at least special, characters that distinguish certain genera. For example, in the genus Cryptoporus the pore surface is covered by a partial veil that has to be mechanically broken or degraded for spore to be released. Pycnoporus is distinguished by its reddish-orange hyphae, but is otherwise microscopically similar to Trametes. Lenzites is also microscopically similar to Trametes, except for the sword-like hyphal ends in the hymenium and the lamellate (gilled) hymenophore.�

It would take several more pages to adequately describe all the nuances of polypore taxonomy. But don�t let that deter you! You can learn many of them very quickly. Since the polypores are a very interesting group of organisms, I encourage you to collect some and try to key them out. Many of the more common ones can be keyed with amateur mushroom guides. There are pictures of many of the species at my world wide web site. Many polypores have been "Fungus of the Month" on my web pages, so check there for more information. The polypores are always present, so you can even collect some of them in the winter in the north.. I guarantee if you start collecting polypores, you�ll never come back from a foray empty-basketed again!

Polypore glossary�

Amyloid � turning blue-black in Melzer�s reagent, which contains iodine�

Annual�a fruiting body lasting only one season�

Binding hyphae�aseptate, many-branched hyphae that bind other types of hyphae together�

Brown rot�type of wood decay in which the fungus uses up the cellulose and leaves brown lignin behind�

Clamps (Clamp connections)�appendages on generative hyphae that maintain the dikaryotic (binucleate) state�

Cystidia�sterile cells between the basidia in the hymenium�

Dextrinoid�turning reddish-brown in Melzer�s reagent�

Dimitic�containing two kinds of hyphae, generative hyphae, plus either skeletal (most often) or binding hyphae�

Effused�flat on the surface of the substrate. See also resupinate�

Effused-reflexed�flat on the surface of the substrate, but turning into a shelf as the substrate turns�

Generative hyphae�thin-walled hyphae for conduction of food and other materials�

Hymenium�the layer of fertile basidia plus associated sterile structures (cystidia)�

Hymenophore�the hymenium bearing surface�

Hypha�the filamentous structures that make up the vegetative or feeding portion of a fungus�

Hyphal system�the aggregation of different types of hyphae for a fruiting body
Monomitic�having only one kind of hyphae (generative hyphae) in the fruiting body�

Melzer�s reagent�reagent composed of iodine plus chloral hydrate (a narcotic controlled substance)�

Mycorrhizal�a fungus having a mutualistic association with the roots of plants�

Perennial�a fruiting body lasting more than one year�

Reflexed�a fruiting body forming a shelf�

Resupinate� a fruiting body flat on the surface. See also effused�

Septa�divisions between cellular compartments in hyphae�

Setae�like cystidia, but thick-walled, pointed, and found in the Hymenochaetaceae�

Simple septa� septa without clamps�

Skeletal hyphae�thick walled structural hyphae�

Trimitic�having three types of hyphae in the fruiting body, generative, skeletal and binding�

White rot�type of wood decay in which the fungus uses the lignin and leaves the white cellulose behind.�

Arora, David, 1986. Mushrooms Demystified. 1991. All that the Rain Promises and More: A hip pocket guide to Western Mushrooms. Berkeley, CA: Ten Speed Press.�

Gilbertson, R.L. and L. Ryvarden. 1986, 1987. North American Polypores Fungiflora. Norway Two Volumes�

Lincoff, Gary, 1981. The Audubon Society Field Guide to North American Mushrooms. New York: Alfred Knopf.�

Overholts, L.O. 1953. Polyporaceae in the United State and Canada. Univ. Michigan press, Ann Arbor. 466 pp.�

Ryvarden, Leif. Genera of Polypores; Nomenclature and Taxonomy. Fungiflora Norway. Synopsis Fungorum 5. 363 pp.�

Volk, Thomas J. Tom Volk�s Fungi Webpage TomVolkFungi.net