Some fungi from Dundas Conservation Area, ON, August 13, 2008 |
White's Mycology PageD. Andrew White M.Sc. 07/21/2010 |
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The Mycota, or the Fungi, are usually conisidered to be a separate taxonomic Kingdom from either plants or animals. True Fungi are eucaryotes with chitin lined cell walls, that live by digesting food substances. They are not directly photosynthetic. Cells tend to be syncytial, the cells run-together into long tube-like multi-nucleate 'hyphae'. This continous cytoplasm is most pronounced in the lower fungi. In the ascomycetes and basidiomycetes, there are partial septa dividing up the hyphal cytoplasm into segments. Most fungi are isogametic, meaning that the gamete mating-types are very similar in size and shape. Fungi often live in soil, but some are parasites on other organisms, including plants. Fungi have many physiological and genetic similarities to animals. The chytrid moulds even produce flagellated gametes, like animal spermatozoa. A sampling of toadstools from Southern Ontario are described in the table below.
Quite a number of fungi live symbiotically with either cyanobacteria or algae. In this manner they become indirectly photosynthetic. These are the lichen fungi. Most lichens are ascomycetes, a few are in other taxa. Lichens are not a natural taxonomic group. Many are in fact closer genetically to non-lichenous fungi than to each other. Lichens are quite widespread. In the boreal forest, and in the tundra zone, lichens can grow on the ground as ‘reindeer moss’. Many species grow on tree bark, and yet other species grow on rock faces.
Fungi take part in a variety of symbiotic relationships - mostly with plants or with algae. Mycorrhizal associations are one widespread kind of symbiosis. In this relationship a plant seemingly trades carbohydrates with a fungus, in exchange for mineral nutrients. Plants are photosynthetic, fungi are not. Fungal mycelium is more able to uptake ionic nutrients more so than plant roots. The mycorrhizal trade therefore benefits both the plant and the fungus. As may be expected, some species of fungus can cheat the system and parasitise the host plant. Parasitic plants do exist. In such situations, the plant exploits the fungus instead.
Some organisms somewhat resemble fungi - but they are not even members of the same taxonomic kingdom as are the Fungi. These organisms are the ‘fungoids’ or fungus-like organisms. The slime moulds are a case in point. Most slime moulds are Myxogastria, they are amoeboid protozoa. Somethings called ‘slime moulds’ are in yet different taxonomic groups. All could be said to be protozoan.
Toadstools & MushroomsToadstools are the larger fruiting bodies of fungi. Generally these are typified by a stipe or column upon which is supported a spore-bearing head. The toadstool form is an adaptation for exposing spores to air currents. Most commonly seen toadstools are members of the phylum Basidiomycota. In the Ascomycota the slippery-caps, morels and lorchels form large toadstools also. Generally speaking, if humans can eat a toadstool, it is called a ‘mushroom’. Some toadstool-forming fungi cause wood decay. But many of the fungi which cause plant diseases are microfungi, with tiny sporocarps. Some, such as the endophytic fungi exist mostly as mycelium, and do not often form fruiting bodies. Many fungi are mycorrhizal, meaning that they live symbiotically with plant roots. Yet others fungi are simply saprobes, they feed on organisms that have already died. Saprobic fungi are common in the humus layers of soil and in the duff layers on forest floors.
Most fungi qualify as multi-cellular organisms. They even have different cell types. Though, the differences between these cell types are rather subtle. The morphogenesis of the fungi is not homologous with animals, and is not even closely analogous. A fungus is vaguely analogous to a plant in some ways. Like a plant, a multi-cellular fungus is a modular organism composed of reiterated units. Most hyphal types are not ‘fated’. Given the appropriate stimulus, a hyphal tip is capable of reverting to some other role. That is, somewhat like plants the ‘somatic’ versus ‘germ-line’ distinction is not too applicable to the fungi. Meiotic cells are not as flexible as most other cell types, once they have been set on course. Otherwise, almost any fragment ripped out of a fungus can act as a ‘stem cell’ and clone itself into a whole new individual. Probably, the fungi derived their multi-cellular condition independently of either plants or animals. In other words, the common ancestor of all three ‘higher’ kingdoms was probably a single-celled protozoon. Genetic comparisons suggest that fungi and animals parted ways roughly one thousand-million years ago in the Early Proterozoic. Fungi are heterotrophic organisms that generally live inside their food media. The true fungi feed by osmotrophy. They lack true phagocytosis. That is, they feed by excreting enzymes, and then reabsorbing the digestible products of these exoenzymes. This mode of life is not unique to fungi. In fact parallel strategies exist in many protozoa and even in the bacteria. In fact many bacteria form ‘mycelia’ somewhat as fungi do. This is why many bacteria were once called ‘bacterial moulds’ and given names such as: ‘ray fungi’ (Actinomycetes), ‘fission fungi’ (Schizomycetes) and mycoplasmas. ReferenceMoore, David. 2005. Principles of Mushroom Developmental Biology. International Journal of Medicinal Mushrooms. 7: 79-101. Morel Mushrooms
Morels have long been considered to be both saprobic and mycorrhizal. However, in the 1990s it was suggested that morels are sometimes parasitic. Morels are certainly saprobes, at least some of the time. This is why it is possible to cultivate morels in vitro, with difficulty. Morels can also be mycorrhizal, they seem to benefit many species of trees and herbs. The morel's mycelium forms mantles around rootlets. Root cells are penetrated with little hyphae (haustoria) and feed off the host plant’s nutrients. Normally this relationship is endo-mycorrhizal. The morel exchanges mineral nutrients, as if by way of trade, for the plant's carbohydrates. The morel's association with roots is not always mycorrhizal. Apparently when roots die, or they are dying, the morel's haustoria harvest the sugars inside the root cells. In this manner morels wait poised to become root-rotting agents, as soon as their role as mycorrhizal fungi is over. Probably the fruiting bodies are an final attempt to reproduce before its food supply runs out. This is the probable explanation for why morel mushrooms seem to be most common under dying trees. It is even possible that morels may switch to a parasitic role as their host tree weakens. Whether or not morels are ever true parasites is still an open question. Morels are not a major cause of root decay. They rot only the most peripheral roots of trees. And it is mostly soluble carbohydrates, not cellulose, that the morels consume. Therefore, morels are not a significant factor in the destruction of root support. Morels are very unlikely to instigate tree falls. Since morels are edible, their growth is often encouraged by landowners. Morels are not considered a pest, rather they are a gift from the earth. Honey Mushrooms
Stumpers are important as agents of wood rot. Some species are considered to be pathogens. Not every species is a pathogen to living trees. It is commonly supposed that the Armillaria mellea is a highly variable species with many subspecies in it. It is now suspected that this species is the most active pathogen in the genus. Hunter’s heart, abortive entoloma, aborted pinkgill or entolome avorté (Entoloma abortivum) is a smallish rather nondescript gilled mushroom. It is edible, and it is prized by mycophages. Its has a pale brown or creamy cap, a light coloured stipe, and it grows on decayed logs. Its taxonomic relatives are known collectively as ‘pinkgills’, because the gills are pinkish. Sometimes these mushrooms seem to occur with deformed caps. Usually this deformity occurs when they grow in close association with honey mushrooms.
Naturally, it was long assumed that the aggressive honey mushroom parasitises the hapless entoloma.
Recent research strongly argues that it is the entoloma which parasitises the honey mushroom.
What were once thought to be distorted entoloma, turned out to be mostly composed of the honey-mushroom’s tissue.
Apparently, the ‘aborted’ mushrooms are deformed honey mushrooms riddled with feeding mycelia from the entoloma!
Such deformed toadstools are called carpophoroids.
Often malformed fungal masses are due to parasites of one kind or another (Czederpiltz et al 2001).
Ceps & Boletes
The genus Boletus is typified by toadstools with stout smooth stipes, rounded caps, and with pores under the cap. Most species are tan, brown, ochre, golden or reddish. The reddish species tend to be less flavorsome, sometimes they are even bitter, or even poisonous. Boletes are generally mycorrhizal. The exceptions tend to be parasites on other fungi. In the boreal forest one often finds boletes neatly tucked between the twigs of spruce trees. These boletes were not placed there by trolls! They were collected by squirrels. Many boletes apparently exploit rodents as agents of dispersal. Boletes in general are similar to the polypore toadstools - but much more like agaric ‘mushrooms’ in shape. Once it was thought that boletes were closely related to the genus Suillus. The suillus toadstools are similar in appearance, but often have rough textured stipes and larger pores. It is now known that this similarity does not reflect genetic closeness. Boletes are genetically closer to some of the gilled-toadstools than to the suilli. Furthermore, recent research indicated that there many more bolete species than hitherto expected. Many of these species are extremely close look-alikes, differing in their mycorrhizal associations and other subtle details. The bitter bolete (Tylopilus felleus) is not a true bolete. Unfortunately this terrible tasting toadstool is more common in Ontario's boreal forest than is the edible bolete. It is one of the few non-red bolete-like fungi that is not edible. It differs in appearance from the edible bolete mostly in subtle details of form. False-Truffles
The 'true' truffles are ascomycetes - not basidiomycetes. Rather than being stunted toadstools, they are deformed cup-fungi. That is, their fruiting bodies are derived from apothecia that are crumpled-up. The pine-truffles, in the genus Geopora, are obviously apothecial in structure. In the Tuber genus the apothecial 'cups' are not nearly as obvious. Ascomycete truffles are hypogeous and mycorrhizal. They rely on animals for spore dispersal. Jack o’Lanterns
Superficially the fully expanded jack o' lantern toadstool looks like a chanterelle. Unlike the chanterelle the jack o’ lantern toadstool does have distinct gills. The true chanterelles have ridge-like rills instead of distinctly formed gills. The jack o’ lantern toadstool is fairly poisonous. The toadstool sometimes glows brightly enough to be visible on dark nights. In French the fungus is known as the clitocybe lumineux because of its bioluminescence. Psilocybes
Psilocybes are one of the few toadstools to become embroiled in mythology and pseudoscience. Because of their popularity as hallucinogens, there has been much exaggeration about the safety and danger of these shrooms. Amanitas
Taxonomy & BiologyFungi are typified by the fact that they can have two distinct kinds of spore types. They can have a sexual phase (the teleomorph), or they can disperse via an asexual phase (the anamorph). These spores can be quite different in form. Furthermore, many species of fungus produce one spore type much more often than the other. Since hyphae look so much alike, it has often been difficult to determine the connection between the asexual and sexual forms. Hence the fact that many fungi have been given two species names! Only with the advent of genetic analysis are many of the anamorphs and teleomorphs being matched up. Some fungi seldom, if ever, take on a teleomorphic phase, these fungi imperfecti reproduce asexually most of the time. Spores produced on fruiting-bodies are usually haploid. In fact, a growing mass of fungal tissue (the mycelium) can be haploid. This haploid mycelium may clone itself with asexual spores. When two mycelial filaments (hyphae) of opposite mating types (sexes) meet they fuse. In the non-chytrid fungi this initial sexual fusion is incomplete. The union of the two hyphae produces a dikaryotic hypha, a tissue with two sets of nuclei. A dikaryotic mycelium may then grow from this union. The mycelium may grow for a long time-period without complete sexual fusion taking place. Actual sexual fusion of the nuclei occurs during the formation of a fruiting-body (sporocarp). In other words, a toadstool appears as the sexual fusion is in progress.
Toadstools are merely the fruiting bodies of the fungus. The greater mass of a fungus is mycelium. In fact, altogether some fungi are composed of tonnes of mycelial clones extending through hectares of soil. Technically, some fungal mats are the largest known organisms on Earth. Certainly a soil fungus can be larger than a baleen whale, a redwood tree, or a whole stand of poplar clones! Although, some would argue that masses of cloned mycelium don’t count as single individuals. Soil Fungi
Saprobes are organisms which live by digesting the remains of other living things. Sometimes this means obtaining food from waste products. But it also means digesting organisms which have already died. Basically, all heterotrophs (i.e. non-autotrophs) rely on other organisms for food. Predators and parasites obtain this food by actively feeding on living tissues. Saprobes are more like scavengers. They obtain their nutrients from other organisms - but not via parasitism, predation or direct herbivory. Saprobic organisms are a major part of the edaphic flora and fauna. It is saprobic organisms which generate the humus component in top soil. Because of saprobes, dead organisms are reduced to microscopic organic particles and emulsions. The broken down bio-matter forms the humus which lends the top soil its dark colour. This also allows the the organic matter to be re-useable by plants. One litre of top soil can contain literally millions of individual bacteria, fungi, oomycetes and sundry protozoa. Some of these creatures are free-living, others form biofilms on mineral particles in the soil. Fungi are the second most massive living component in soil after bacteria. Insects, and other animals, account for but a tiny fraction of the biomass in dirt.
Fungi play a crucial role in terrestrial ecosystems. Fungi have managed to occupy a greater number of niches on land than they do in the sea. Soil fungi live-off everything from dead bacteria, to dead animals, to dead wood. It has been estimated that fungi may comprise up to twenty percent (20%), or more, of the living biomass on land. Much of the remaining biomass consists of dead plant matter and bacteria.
The number of fungal species which have a niche in soil ecosystems is immense. Most of the moulds are zygomycete pin-moulds, members of the Phylum Archaemycota. The Rhizopus and Mucor species are common pin-moulds, which can occur in soils, or on rotten plant matter. Both of these pin-moulds can infect wounds in animals, under unusual conditions. Zygorrhynchus are common pin-moulds in humus. Some of the pin-moulds, such as Arthrobotrys, are both saprobic and predaceous. A nematode, once subdued, is then penetrated by the feeding hyphae of the mould. The niches in soil ecosystems are not always sharply defined. Some of the soil fungi are glomeromycetes, others are ascomycetes or basidiomycetes. Some are microfungi, others form large toadstools. The Endogone are common soil fungi, some of which are mycorrhizal. The endogone moulds are now known to be related to the aquatic chytridiomycetes. Some of the soil moulds, such as Saprolegnia, are oomycetes, and not really fungi. Some of the soil fungi grow best on fresh dung. They do not proliferate well in soil lacking fresh organic matter. The well-studied Phycomyces grows on dung, and other relatively ‘fresh’ organic matter. The Phycomyces hypha can sense light, and grow towards it. In this way it can seek out an open space in which to release its spores. The ‘hat-thrower’ fungi in the genus Pilobolus have a rather interesting means of projecting their spores. When mature, the hat-thrower shoots its sporangium a great distance with the hydrostatic pressure of a sporangiophore ‘connon’. The spore masses may then stick to grass blades, where they could be eventually be swallowed by herbivores. The sprores can survive the digestive tracts of animals. These several dispersal mechanisms of dung fungi allow them to disperse to other dung piles, which may be rather far from one another. Yeasts are unicellular fungi. Strangely, they are not usually members of the Archaemycota. Yeasts are generally ascomycetes, and some even form short hyphae, and many sprout little asci. Yeasts, such as the Saccharomyces, are usually saprobic in one way or another. They live much like protozoa in the organic matter of humus. Quite a high proportion of the moulds are fungi imperfecti, or asexual fungi. Imperfect moulds are usually, but not always, ascomycetes. Fungi in the genus Alternaria are common soil fungi. If alternaria grows indoors it is called ‘black mildew’, and it can be strongly allergenic. The mildew-like Cladosporium fungi are are common in rich humus. Aspergillus and Penicillium moulds, with their bluish conidia, are a common in both humus and in freshly rotting plant matter. Some of these moulds appear to live in both saprobic and parasitic niches. This appears to be the case for some of the Verticillium wilts. Some ‘verticillium’ moulds are parasites, others feed on root exudes, and others can grade into true saprobes. Most of hitherto mentioned imperfect ‘genera’ are anamorph names. The teleomorphic names of the sexual forms are taxonomically more accurate. However, in many cases, the individual species are known only from their anamorphic states. Usually more than one genus occurs within each anamorphic type. Many of the soil fungi live off of the sugary exudes of plant roots. These niches grade into the true mycorrhizae. Mycorrhizal fungi are actively symbiotic in that they aid plants' roots in the absorption of nutrients. These true mycorrhizae include such macro-fungi as the toadstools and the hypogeous truffles and tuckahoes. ReferencesCzederpiltz, Daniel L. Lindner; Volk, Thomas J.; Burdsall, Harold H., Jr. 2001. Field observations and inoculation experiments to determine the nature of the carpophoroids associated with Entoloma abortivum and Armillaria. Mycologia. 93(5): 841-851. Freinkel, Susan. 2002. If all the trees fall in the forest ... Discover. 23 (12) 67-73. Grubisha, L.C. Trappe, J.M. Molina, R. and Spatafora, J.W. 2001. Biology of the ectomycorrhizal genus Rhizopogon. V. Phylogenetic relationships in the Boletales inferred from LSU rDNA sequences. Mycologia 93(1): 82–89. Hagen, Bruce W. 2001. Sudden Oak Death Part 1: symptoms, biology and potential impact. Arborist News. 10(6):29-31. Heinrich, Bernd. 1997. The Trees in My Forest. Cliff Street Books. New York. Holiday, Paul. 1989. A Dictionary of Plant Pathology. Cambridge University Press. New York. 140-141, 233-240. Margulis, Lynn and Sagan, Dorian. 1995. What is Life? Simon & Schuster. New York. Money, Nicholas, P. 2002. Mr. Bloomfield’s Orchard - the mysterious world of mushrooms, molds, and mycologists. Oxford University Press. New York. Schwarze, F.W.M.R., Engels, J. and Mattheck, C. 2004. Fungal Strategies of Wood Decay in Trees. Springer. Berlin. Thorn, R. Greg. 1991. Mushrooms of Algonquin Provincial Park. The Friends of Algonquin Park. Whitney Ontario. Tudge, Colin. 2000. The Variety of Life. Oxford University Press. Oxford. 127-157. |
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