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.

	Eyelash Cup - Pézize en bouclier - Scutellinia scutellata (L.) Lambotte: Eyelash cup fungi are ascomycetes in the Pyronemataceae family. The fruiting bodies are small disc shaped apothecia, usually less than a centimetre wide. These discs can occur in fairly large clusters. These are often orange or bright red, with an oily spore bearing surface. These cups are rimmed by small dark hair-like fibres –the so-called ‘eyelashes’. It is possible that insects are somehow recruited to carry the spores. The mycelia of this fungus grow usually in rotting wood, dung or other rich biotic matter. Its fruiting bodies often accompany mosses, slime moulds and other cryptogams.
	White Coral Fungus - Ramaire de Kunz - Ramariopsis kunzei (Fr.) Corner : The white coral fungus is in the Clavariaceae family. They are basidiomycetes, even though they resemble some of the ascomycetes in form. This toadstool is branched, coral-like, and only a few centimetres tall. It occurs in troops on forest duff, or on very decayed wood It tends to be associated with forest clearings and even with grassy areas. Apparently it is a saprobic fungus. The white coral fungus is without 'gills', the spores develop near its branch tips. It fruits in the typical toadstool window from summer to late autumn. It is considered to be edible, but the small toadstools are not considered very flavourful.
	Scaly Inky Caps - Coprin écailleux - Coprinus quadrifidus Pk.: The true ink-caps, or inky caps, are members of the Agaricaceae family. The shaggy mane (C. comatus) is the most well known species, because it often appears on lawns. The Latin, and French, genus names imply that the toadstools grow on dung. But most species grow in rich humus. The scaly or variegated inky cap grows in clusters on hardwood debris in forests. The gills are enclosed in a bell-shaped cap. The caps deliquesce to release their spores. The black 'inky' dissolving caps accounts for their English name - ‘inky caps’. These oblong toadstools appear mostly in the summer. They are mildly poisonous, especially if eaten with alcohol. But they can be eaten, if cooked very thoroughly.
	Trooping Crumble Caps - Coprin disséminé - Coprinellus disseminatus (Pers.) J.E. Lange: Trooping crumble caps are gilled toadstools in the Psathyrellaceae family. These toadstools occur usually in large ‘troops’ on rotten stumps and logs. The toadstools appear from the late spring until the autumn. The fungus grows in both exposed rotten wood and in slightly buried wood. The toadstool’s cap is beige, and only about 1 to 2 cm wide. The caps are deeply grooved on the upper side. Though distant relatives of the ink-caps, the fungus has lately been assigned to a separate family and genus. The gills are non-deliquescent - unlike the true ink-caps of the genus Coprinus. The toadstool is considered to be edible. But it is seldom harvested, due to its small size.
	Blewit – Tricholome pied bleu - Clitocybe nuda (Bull. Fr.) H.E. Bigelow: Blewits are gilled mushrooms in the Tricholomataceae family. They have violet to lavender coloured gills, caps and stems. Blewits commonly grow under spruce trees in the needle duff. Blewits are widespread in both Eurasia and in North America. They have apparently become naturalised in Australia. They are one of the most visually striking of the temperate toadstools. The large caps, 5 to 15 cm wide, usually appear in the late autumn. Blewits have a pleasant fruity smell, but a somewhat acrid taste. The blewit is an esteemed edible ‘mushroom’. It can be commercially cultivated in wood chips or leaf mulch.
	Elm-Oyster - Chapeau marbré - Hypsizygus ulmarius (Bull.:Fr.) Redhead: Elm-oysters, or marble-caps, are gilled mushrooms in the Tricholomataceae family. The pale caps of the elm-oyster can become quite large, over 15 cm wide. Elm-oyster grows in dead heartwood, most often on elm or Manitoba maple. These caps can sprout quite high in a tree, often they extend from knotholes. The fruiting bodies typically appear in the late autumn. The caps can even persist up until the first frost. A similar species, the H. tessulatus, was for a long time thought to be the same species. This other species has darker caps and it usually does not infect Manitoba maple. Both kinds of elm-oyster are edible. Some people use a knife on a pole to remove them from the taller trees.
	Bark Mycena - Mycéne claviculé - Mycena clavularis (Batsch) Sacc.: The bark mycena is a member of the Tricholomataceae family. The fungus grows on the bark of hardwood trees. The gills in the tiny caps are widely spaced. The pale caps are usually less than 3 mm wide. Troops of these toadstools may appear after rainy weather, most often in the autumn. There are many species of mycena, most of these are saprobes. The bark mycena is notable for its minute caps, and for the fact that it grows on the bark of living trees. Most mycenas grow near the ground in rotting organic matter. Mycenas in general are edible. Though, most are so small that they are not collected.
	Fly Agaric - Amanite tue-mouche - Amanita muscaria var. guessowii Vesely: Amanitas are gilled toadstools in the Amanitaceae family. The fly agaric usually has yellow caps, in the Americas. The Eurasian subspecies tend to be more reddish. The caps are often covered by pale flecks of the veil that adhere to it. It fruits from the summer into the late autumn. The fly agaric is mychorrhizal, mostly on the roots of conifers. It is both poisonous and hallucinogenic. The North American subspecies are generally less hallucinogenic than the Eurasian versions. A poultice made from the fly agaric really can kill house-flies. Most species of amanita are poisonous to some degree.
	White Pine Bolete - Bolet américain - Suillus americanus (Peck) Snell: White pine boletes, or chicken fat mushrooms, are members of the Suillaceae family. The cap has pores, instead of ‘gills’, on its underside. These pores are more oblong than those of true boletes. The cap, the pore surface and the stock are all yellowish in colour. These caps can grow to over one decimetre wide. This mycorrhizal species grows under white pine, and close relatives of the white pine. It is closely related to the S. sibricus of northern Asia. Fruiting bodies are visible from the summer into the autumn. In mixed forests and pine plantations, this ‘bolete’ can occur in very large numbers. It is an esteemed edible mushroom.
	Destructive Pholiota – Pholiote destructrice - Hemipholiota populnea (Pers. : Fr.): The pholiotas and hemipholiotas are ‘gilled’ toadstools in the Strophariaceae family. The caps are cinnamon coloured, with ‘scales’. The toadstool grows in clusters, usually low on a tree's root-crown or on a stump. These caps can appear from July into the late autumn. Most pholiota species are saprobic, but a few are parasitic on live-wood. The wood decay is considered to be a kind of ‘white rot’. Most pholiotas are at least mildly poisonous.
	Common Earthball - Scléroderme vulgaire - Scleroderma citrinum Pers.: Earthball is a kind of ‘false puffball’ with a scaly derma. This basidiomycete is a member of the Sclerodermataceae family. Earthball often has a distinct yellowish tinge, on its outer surface. The earthball manifests its fruiting-bodies mostly from the late summer into the autumn. This saprobe grows on mossy or peaty area, usually in woods with sandy soils. The derma breaks open irregularly to release the dark purple-black spores. The spore mass is less powdery than those of regular puffballs. Unlike most other puffballs, the common earthball is generally considered to be poisonous.
	Oyster Mushroom - Pleurote en forme d’huître - Pleurotus ostreatus (Jacq.) Quél.: Oyster mushrooms are gilled toadstools in the Pleurotaceae family. These fungi feed mostly on rotting wood, where they form off centre toadstools or ‘brackets’. These pale gilled brackets appear mostly in the late autumn. The fungus is actually ‘carnivorous’ - after a fashion. It can paralyse nematodes with the droplets of trans-2-decenedioic acid that it exudes from its mycelia. It then feeds on these eelworms by insinuating its hyphae into the worm's apertures. This dietary supplement probably helps the fungus obtain extra nitrogen. The fungus is an esteemed edible ‘mushroom’. It is now being commercially cultivated.
	Northern Shelving Tooth - l'Hydne septentrional - Climacodon septentrionale (Fr.) Karsten: The northern shelving fungus, or northern tooth fungus, is a soft bracket or conk in the Meruliaceae family. It is in the same family as the Phlebia species, the jelly-rot and jelly-crust fungi. These conks can be quite large, up to several decimetres wide. Massive clusters of these fruiting bodies can occur on tree trunks and on large branches. These fruiting bodies are soft, and they are pale cream-white to light brown in colour. They darken and turn reddish with age. The spores are borne on pointed soft cones - the so-called “teeth”. Its spore surface resembles somewhat those of the bear's-head and hedgehog fungi. The brackets often appear from mid-summer through into the autumn. It is parasitic on hardwoods such as maple and beech. It is not the most serious of the wood parasites, as the fungus mostly infects already wounded wood. Though, in rotting-out the heartwood this can structurally weaken a tree. The fungus is not considered to be edible.
	Late Fall Polypore – Polypore fuligineux - Ischnoderma resinosum (Schrad.) P. Karst: Late fall polypore is one of the bracket or ‘conk’ fungi. It is a member of the Hapalopilaceae family of polypores. The brackets are velvety red-brown on top, with a white spore surface below. The brackets can grow up to 15 cm wide. The spores are borne in tiny pores, each less than 0.2 mm wide. Its mycelium lives mostly in dead hardwood. (It has a close relative, the I. benzoinum, that can live in conifer wood.) The fruiting bodies of the polypore appear in the late autumn. The bracket is relatively soft - being somewhat rubbery in texture. When wounded it may exude a resin-like liquid with a strong odour of ‘anise’. Though not poisonous, the late fall polypore is not generally eaten.

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.

Pixie-cup Cladonia – Cladonie difforme - Cladonia chlorophaea (Flörke ex Sommerf.) Spreng.: This ‘reindeer moss’ is an ascomycete in the Cladoniaceae family. This lichen is sometimes called ‘false pixie-cup’. The spores form on small green-grey discs or ‘apothecia’. In this lichen, the apothecia look somewhat like golf tees. It grows on the ground in mossy patches, often in forest clearings. These lichens contain symbiotic chlorophyte algae (Trebouxia). The fungus obtains its carbohydrates via the photosynthesis of its algal symbionts.

Cryptic Rosette Lichen - Physcielle cryptique - Physciella chloantha (Ach.) Essl.: The physciella lichen is in the Physciaceae family. It usually grows on tree bark, but occasionally also on limestone. It is foliose with rather small lobes on its leafy thallus. The undersides are pale brown, the upper surface is grey-green to bright green. The fruiting bodies are fairly small, and they infrequently appear. Like most lichens, little fragments of the thallus can break off to found new colonies. These ‘soralia’ contain both the fungal and the algal symbionts. It is one of the green lichens that can be mistaken for a moss. The lichen utilizes Trebouxia algae as its photobionts.

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.

Bird’s Nest Pinesap - Monotrope sucepin - Monotropa hypopitys L.: Pinesap is a flowering plant, not a fungus. It is a member of the heath or Ericaceae family. Pinesaps are achlorophyllous plants that have lost their photosynthesis. Pinesaps are mycoheterotrophs, they parasitise mycorrhizal fungi, i.e. they are mycorrhizal cheats. Various Monotropa species parasitise a variety of fungal species, such as the brittle-gills and boletes. The bird's nest pinesap is a parasite of the Tricholoma toadstools. These toadstools tend to gain carbohydrates from tree roots, often those of conifers. The bird’s nest pinesap grows most often under pines and oaks. It prefers acidic soils, and it commonly occurs in boreal forests and pine-oak parklands. It is quite common in Ontario. This plant has yellowish vestigial leaves. It has several flowers per stock, unlike some other pinesaps. The plant spends much of the year underground, coming to the surface only to flower. The reddish flowers bloom from mid-summer into the late autumn.

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.

Multigoblet Slime - Métatrichie en nid - Metatrichia vesparium (Batsch) Nan.-Brem.: Metatrichia vesparium is a slime mould in the Trichiaceae family. Each fruiting body looks like a tiny metallic club, or a packet of clubs. The club breaks at its apex to form a little ‘goblet’ containing the spores. The spongy spore mass is often vivid orange or even red. During their amoeboid phase they feed mostly on other microbes. To form spores, many separate amoeboid cells condense into bigger blobs. These large blobs in turn transform into the tiny ‘toadstools’ - the sporangia. Metatrichia slimes live on moist dead-wood, dead bark or on plant debris. The sporangia form just after bouts of rainy weather.

Carnival Candy Slime - Arcyrie dénudée - Arcyria denudata (L.) Wettst.: Carnival candy slimes are members of the Arcyriaceae family. They live mostly on and within moist deadwood. In its amoeboid stage it feeds on other microbes. The amoeboid plasmodium condenses into the fruiting bodies or sporangia. The reddish and fuzzy sporangia vaguely resemble ‘cotton candy’ on a stick. Each sporangium breaks open at maturity, and the spongy spore mass inside is then exposed. The sporangia are usually less than 7 mm tall. These sporangia appear during the summer and the autumn.

Toadstools 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.

	Ascomycota Ascospores: Spores in sac-like 'asci'. Sexual ascospores are generally borne on the surface of the sporocarp. Often the spores are on the upperside of the ‘toadstool’. Spore-bearing surface can be a matrix of many apothecia or perithecia.
	Basidiomycota Basidiospores: Spores borne on club-shaped 'basidia'. Sexual basidiospore layer usually on the underside of the toadstool cap or bracket. The spore bearing surface usually originates inside the sporocarp. A tissue-cover breaks to expose this spore-bearing tissue.

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.

Reference

Moore, David. 2005. Principles of Mushroom Developmental Biology. International Journal of Medicinal Mushrooms. 7: 79-101.

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).

For more information on this story visit Dr. Tom Volk's Fungi Page .

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 & Biology

Fungi 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.

Sporocarp Type	Forms	Sporocarp Characteristics
Sporangium (pl. Sporangia):		Sexual or asexual spores in sac-like ‘pin-head’ on a stock.
Conidium (Conidia):		Asexual spores exposed on hyphal stocks.
Chlamydospore:		Asexual spores formed by hyphal division & swelling.
Pycnidium (Pycnidia):		Flask-shaped organ containing asexual conidia.
Apothecium (Apothecia):		Cone or cup-shaped organ containing sexual spores.
Perithecium (Perithecia):		Flask-shaped organ containing sexual spores.

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.

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.

References

Czederpiltz, 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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