Lichens
TABLE OF CONTENTS
- Lichens
- Evolution and phylogeny of fungi
- Outline of classification of fungi
- Classification of the fungi
Basic features of lichens
A
lichen is an association between one or two fungus species and an
alga or cyanobacterium (
blue-green alga) that results in a form distinct from the symbionts. Although lichens appear to be single plantlike organisms, under a microscope the associations are seen to consist of millions of cells of algae (called the
phycobiont) woven into a matrix formed of the filaments of the fungi (called the
mycobiont). Many mycobionts are placed in a single group of Ascomycota called the Lecanoromycetes, which are characterized by an open, often button-shaped fruit called an apothecium. Although lichens had long been assumed to consist of a single fungus species and a single phycobiont, research suggests that many macrolichens also feature specific basidiomycete yeasts in the cortex of the organism. There are various types of phycobionts, though half the lichen associations contain species of
Trebouxia, a single-celled
green alga. There are about 15 species of cyanobacteria that act as the photobiont in lichen associations, including some members of the genera
Calothrix,
Gloeocapsa, and
Nostoc.
Authorities have not been able to establish with any certainty when and how these associations evolved, although lichens must have evolved more recently than their components and probably arose independently from different groups of fungi and algae or fungi and cyanobacteria. It seems, moreover, that the ability to form lichens can spread to new groups of fungi and algae. Lichens are a biological group lacking formal status in the taxonomic framework of living organisms. Although the mycobiont and phycobiont have Latin names, the product of their interaction, a lichen, does not. Earlier names given to lichens as a whole are considered names for the fungus alone, and much of the problem lies in the fact that the taxonomy of lichens was established before their dual nature was recognized; i.e., the association was treated as a single entity. Classification of lichens is difficult and remains controversial, though genetic analyses of the symbionts in a given lichen may serve to clarify the taxonomy of the group.
Approximately 15,000 different kinds of lichens, some of which provide forage for
reindeer and products for humans, have been described. Some lichens are leafy and form beautiful rosettes on rocks and tree trunks; others are filamentous and drape the branches of trees, sometimes reaching a length of 2.75 metres (9 feet). At the opposite extreme are those smaller than a pin head and seen only with a magnifying lens. Lichens grow on almost any type of surface and can be found in almost all areas of the world. They are especially prominent in bleak, harsh regions where few plants can survive. They grow farther north and farther south and higher on mountains than most plants.
The
thallus of a lichen has one of several characteristic growth forms: crustose, foliose, or fruticose (
see below Form and function of lichens).
Crustose thalli, which resemble a crust closely attached to a surface, are drought-resistant and well adapted to dry climates. They prevail in deserts, Arctic and Alpine regions, and ice-free parts of Antarctica.
Foliose, or leafy, thalli grow best in areas of frequent rainfall; two foliose lichens,
Hydrothyria venosa and
Dermatocarpon fluviatile, grow on rocks in
freshwater streams of
North America.
Fruticose (stalked) thalli and filamentous forms prefer to utilize water in vapour form and are prevalent in humid, foggy areas such as seacoasts and mountainous regions of the tropics.
Humans have used lichens as food, as medicine, and in
dyes. A versatile lichen of economic importance is
Cetraria islandica, commonly called
Iceland moss and sometimes used either as an appetite stimulant or as a foodstuff in reducing diets; it has also been mixed with bread and has been used to treat diabetes, nephritis, and catarrh. In general, however, lichens have little medical value. One lichen,
Lecanora esculenta, is reputed to have been the
manna that fell from the skies during the biblical
Exodus and has served as a food source for humans and domestic animals.
Lichens are well known as
dye sources. Dyes derived from them have an affinity for
wooland
silk and are formed by decomposition of certain lichen acids and conversion of the products. One of the best-known lichen dyes is
orchil, which has a purple or red-violet colour. Orchil-producing lichens include species of
Ochrolechia,
Roccella, and
Umbilicaria.
Litmus, formed from orchil, is widely used as an acid-base indicator. Synthetic
coal tar dyes, however, have replaced lichen dyes in the textile industry, and orchil is limited to use as a food-colouring agent and an acid-base indicator. A few lichens (e.g.,
Evernia prunastri) are used in the manufacture of
perfumes.
Caribou and
reindeer depend on lichens for two-thirds of their food supply. In northern Canada an acre of land undisturbed by animals for 120 years or more may contain 250 kg (550 pounds) of lichens; some forage lichens that form extensive mats on the ground are
Cladonia alpestris,
C. mitis,
C. rangiferina, and
C. sylvatica. Arboreal lichens such as
Alectoria,
Evernia, and
Usnea also are valuable as forage. An acre of mature black
spruce trees in northern Canada, for example, may contain more than 270 kg (595 pounds) of lichens on branches within 3 metres (10 feet) of the ground.
Form and function of lichens
Although the fungal symbionts of many lichens have fruiting structures on or within their thalli and may release numerous
spores that develop into fungi, indirect evidence suggests that natural unions of fungi and algae occur only rarely among some lichen groups, if indeed they occur at all. In addition, free-living potential phycobionts are not widely distributed; for example, despite repeated searches, free-living populations of
Trebouxia have not been found. This paradox, an abundance of fungal spores and a lack of algae capable of forming associations, implies that the countless spores produced by lichen fungi are functionless, at least so far as propagation of the association is concerned. Some photobionts, including species of
Nostoc and
Trentpohlia, can exist as free-living populations, so that natural reassociations could occur in a few lichens.
Some lichens have solved or bypassed the problem of re-forming the association. In a few lichens (e.g., Endocarpon, Staurothele) algae grow among the tissues of a fruiting body and are discharged along with fungal spores; such phycobionts are called hymenial algae. When the spores germinate, the algal cells multiply and gradually form lichens with the fungus. Other lichens form structures, especially soredia, that are effective in distributing the association. A soredium, consisting of one or several algal cells enveloped by threadlike fungal filaments, or hyphae, may develop into a thallus under suitable conditions. Lichens without soredia may propagate by fragmentation of their thalli. Many lichens develop small thalloid extensions, called isidia, that also may serve in asexual propagation if broken off from the thallus.
In addition to these mechanisms for propagation, the individual symbionts have various methods of reproduction. For example, ascolichens (lichens in which the dominant mycobiont is an ascomycete) form fruits called ascocarps that are similar to those of free-living ascomycetes, except that the mycobiont’s fruits are capable of producing spores for a longer period of time. The algal symbiont within the lichen thallus reproduces by the same methods as its free-living counterpart.
Most lichen phycobionts are penetrated to varying degrees by specialized fungal structures called
haustoria.
Trebouxialichens have a pattern in which deeply penetrating haustoria are prevalent in associations lacking a high degree of thalloid organization. On the other hand, superficial haustoria prevail among forms with highly developed thalli.
Lecanora and
Lecidea, for example, have individual algal cells with as many as five haustoria that may extend to the cell centre.
Alectoriaand
Cladonia have haustoria that do not penetrate far beyond the algal cell wall. A few phycobionts, such as
Coccomyxa and
Stichococcus, which are not penetrated by haustoria, have thin-walled cells that are pressed close to fungal hyphae.
The flow of nutrients and metabolites between the symbionts is the basic foundation of the symbiotic system. A simple
carbohydrate formed in the algal layer eventually is excreted, taken up by the mycobiont, and transformed into a different carbohydrate. The release of carbohydrate by the phycobiont and its conversion by the mycobiont occur rapidly. Whether the fungus influences the release of carbohydrate by the alga is not known with certainty, but it is known that carbohydrate excretion by the alga decreases rapidly if it is separated from the fungus.
Carbohydrate transfer is only one aspect of the symbiotic interaction in lichens. The alga may provide the fungus with
vitamins, especially
biotin and
thiamine, important because most lichen fungi that are grown in the absence of algae have vitamin deficiencies. The alga also may contribute a substance that causes structural changes in the fungus since it forms the typical lichen thallus only in association with an alga.
One contribution of the fungus to the
symbiosis concerns absorption of water vapour from the air; the process is so effective that, at high levels of air humidity, the phycobionts of some lichens
photosynthesize at near-maximum rates. The upper region of a thallus provides shade for the underlying algae, some of which are sensitive to strong light. In addition, the upper region may contain pigments or crystals that further reduce light intensity and act as filters, absorbing certain wavelengths of light.
Lichens synthesize a variety of unique organic compounds that tend to accumulate within the thallus; many of these substances are coloured and are responsible for the red, yellow, or orange colour of lichens.
A lichen thallus or composite body has one of two basic structures. In a homoiomerous thallus, the algal cells, which are distributed throughout the structure, are more numerous than those of the fungus. The more common type of thallus, a heteromerous thallus, has four distinct layers, three of which are formed by the fungus and one by the alga. The fungal layers are called upper cortex, medulla, and lower cortex. The upper cortex consists of either a few layers of tightly packed cells or hyphae that may contain pigments. A cuticle may cover the cortex. The lower cortex, which is similar in structure to the upper cortex, participates in the formation of attachment structures called rhizines. The medulla, located below the algal layer, is the widest layer of a heteromerous thallus. It has a cottony appearance and consists of interlaced hyphae. The loosely structured nature of the medulla provides it with numerous air spaces and allows it to hold large amounts of water. The algal layer, about three times as wide as a cortex, consists of tightly packed algal cells enveloped by fungal hyphae from the medulla.
A heteromerous thallus may have a stalked (fruticose), crustlike (crustose), or leafy (foliose) form; many transitional types exist. It is not known, moreover, which growth form is primitive and which is advanced. Fruticose lichens, which usually arise from a primary thallus of a different growth form (i.e., crustose, foliose), may be shrubby or pendulous or consist of upright stalks. The fruticose form usually consists of two thalloid types: the primary thallus is crustlike or lobed; the secondary thalli, which originate from the crust or lobes of the primary thallus, consist of stalks that may be simple, cup-shaped, intricately branched, and capped with brown or red fruiting bodies called apothecia. Fruticose forms such as
Usnea may have elongated stalks with a central solid core that provides strength and elasticity to the thallus.
The crustose thallus is in such intimate contact with the surface to which it is attached that it usually cannot be removed intact. Some crustose lichens grow beneath the surface of bark or rock so that only their fruiting structures penetrate the surface. Crustose lichens may have a hypothallus—i.e., an algal-free mat of hyphae extending beyond the margin of the regular thallus. Crustose form varies: granular types such as Lepraria, for example, have no organized thalloid structure; but some Lecanora species have highly organized thalli, with lobes that resemble foliose lichens lacking a lower cortex.
The foliose forms are flat, leaflike, and loosely attached to a surface. The largest known lichens have a foliose form; species of
Sticta may attain a diameter of about a metre. Other common foliose genera include
Cetraria,
Parmelia,
Peltigera, and
Physcia.
Umbilicaria, called the common
rock tripe, differs from other foliose forms in its mode of attachment in that its platelike thallus attaches at the centre to a rock surface.
The complex fruiting bodies (ascocarps) of lichen fungi are of several types. The factors that induce fruiting in lichens have not been established with certainty. Spores of lichen fungi (
ascospores) are of extremely varying sizes and shapes; e.g.,
Pertusaria has one or two large spores in one
ascus (saclike bodies containing the ascospores), and
Acarosporamay have several hundred small spores per ascus. Although in most species the ascospore generally has one
nucleus, it may be single-celled or multicellular, brown or colourless; the
Pertusaria spore, however, is a single cell containing 200 nuclei. Another type of fungal spore may be what are sometimes called spermatia (male fungal sex cells) or
pycnidiospores; it is not certain that these structures have the ability to germinate and develop into a fungal colony. Few lichen fungi produce
conidia, a type of asexual spore common among ascomycetes.
The metabolic activity of lichens is greatly influenced by the water content of the thallus. The rate of
photosynthesis may be greatest when the amount of water in the thallus is from 65 to 90 percent of the maximum. During drying conditions, the photosynthetic rate decreases; below 30 percent it is no longer measurable. Although respiration also decreases rapidly below 80 percent water content, it persists at low rates even when the thallus is air-dried. Since lichens have no mechanisms for water retention or uptake from the surface to which they are attached, they very quickly lose the water vapour they absorb from the air. The rapid drying of lichens is a protective device; i.e., a moisture-free lichen is more resistant to temperature and light extremes than is a wet one. Frequent drying and wetting of a thallus is one of the reasons lichens have a slow growth rate.
Maximum photosynthesis in lichens takes place at temperatures of 15–20 °C (59–68 °F). More light is needed in the spring and summer than in the winter. The photosynthetic apparatus of lichens is remarkably resistant to cold temperatures. Even at temperatures below 0 °C (32 °F), many lichens can absorb and fix considerable amounts of
carbon dioxide. Respiration is much less at low temperatures so that, in nature, the winter months may be the most productive ones for lichens.
Evolution and phylogeny of fungi
Fungi have ancient origins, with evidence indicating they likely first appeared about one billion years ago, though the
fossil record of fungi is scanty. Fungal hyphae evident within the tissues of the oldest plant fossils confirm that fungi are an extremely ancient group. Indeed, some of the oldest terrestrial plantlike fossils known, called
Prototaxites, which were common in all parts of the world throughout the
Devonian Period (419.2 million to 358.9 million years ago), are interpreted as large saprotrophic fungi (possibly even
Basidiomycota). Fossils of
Tortotubus protuberans, a filamentous fungus, date to the early
Silurian Period (440 million years ago) and are thought to be the oldest known fossils of a terrestrial organism. However, in the absence of an extensive fossil record, biochemical characters have served as useful markers in mapping the probable evolutionary relationships of fungi. Fungal groups can be related by cell wall composition (i.e., presence of both
chitin and alpha-1,3 and alpha-1,6-glucan), organization of
tryptophan enzymes, and synthesis of
lysine (i.e., by the aminoadipic acid pathway). Molecular phylogenetic analyses that became possible during the 1990s have greatly contributed to the understanding of fungal origins and evolution. At first, these analyses generated evolutionary trees by comparing a single gene sequence, usually the small subunit ribosomal
RNA gene (
SSU rRNA). Since then, information from several
protein-coding genes has helped correct discrepancies, and phylogenetic trees of fungi are currently built using a wide variety of data largely, but not entirely, molecular in nature.
Until the latter half of the 20th century, fungi were classified in the
plant kingdom (subkingdom Cryptogamia) and were separated into four classes: Phycomycetes, Ascomycetes, Basidiomycetes, and Deuteromycetes (the latter also known as Fungi Imperfecti because they lack a sexual cycle). These traditional groups of fungi were largely defined by the morphology of sexual organs, by the presence or absence of hyphal cross walls (septa), and by the degree of
chromosome repetition (ploidy) in the nuclei of vegetative
mycelia. The
slime molds, all grouped in the subdivision Myxomycotina, were also included in Division Fungi.
In the middle of the 20th century the three major kingdoms of multicellular
eukaryotes, kingdom Plantae, kingdom
Animalia, and kingdom Fungi, were recognized as being absolutely distinct. The crucial character difference between kingdoms is the mode of nutrition:
animals (whether single-celled or multicellular) engulf food; plants
photosynthesize; and fungi excrete digestive
enzymes and absorb externally digested nutrients. There are other notable differences between the kingdoms. For example, whereas animal cell membranes contain
cholesterol, fungal cell membranes contain
ergosterol and certain other polymers. In addition, whereas plant cell walls contain
cellulose (a
glucose polymer), fungal cell walls contain
chitin (a glucosamine polymer). One exception to this rule is a group of fairly ubiquitous microscopic fungi (referred to as the
cryptomycota), members of which average about 3 to 5 μm (1 μm is about 0.000039 inch) in length, have cell walls lacking chitin, and possess a
flagellum. Phylogenetic analyses of ribosomal RNA in this clade suggest that it is an ancient fungal group.
Genomic surveys show that plant genomes lack
gene sequences that are crucial in animal development, animal genomes lack gene sequences that are crucial in plant development, and fungal genomes have none of the sequences that are important in controlling multicellular development in animals or plants. Such fundamental genetic differences imply that animals, plants, and fungi are very different cellular organisms. Molecular analyses indicate that plants, animals, and fungi diverged from one another almost one billion years ago.
Although fungi are not plants, formal recognition of fungal nomenclature is governed by the International Code of Botanical Nomenclature. In addition, the taxon “phylum” is used in fungal nomenclature, having been adopted from animal taxonomy. The phylogenetic classification of fungi is designed to group fungi on the basis of their ancestral relationships, also known as their phylogeny. The genes possessed by organisms in the present day have come to them through the lineage of their ancestors. As a consequence, finding relationships between those lineages is the only way of establishing the natural relationships between living organisms. Phylogenetic relationships can be inferred from a variety of data, traditionally including
fossils, comparative
morphology, and
biochemistry, although most modern
phylogenetic trees (evolutionary trees, or cladograms) depend on molecular data coupled with these traditional forms of data.
Kingdom Fungi, one of the oldest and largest groups of living organisms, is a monophyletic group, meaning that all modern fungi can be traced back to a single ancestral organism. This ancestral organism diverged from a common ancestor with the animals about 800 million to 900 million years ago. Today many organisms, particularly among the phycomycetes and slime molds, are no longer considered to be true fungi, even though mycologists might study them. This applies to the
water molds (e.g., the plant pathogen
Phytophthora, the cause of potato late
blight), all of which have been reclassified within the kingdom Chromista (phylum Oomycota). Similarly, the Amoebidales, which are parasitic or commensal on living
arthropodsand were previously thought to be fungi, are considered to be
protozoan animals. None of the slime molds are placed in kingdom Fungi, and their relationship to other organisms, especially animals, remains unclear.
Kingdom Fungi has gained several new members on the basis of molecular phylogenetic analysis, notably
Pneumocystis, the
Microsporidia, and
Hyaloraphidium.
Pneumocystis jirovecii causes
pneumonia in mammals, including humans with weakened
immune systems; pneumocystis pneumonia (PCP) is the most common opportunistic infection in people with human immunodeficiency virus (HIV) and has been a major cause of death in people with
AIDS.
Pneumocystis was initially described as a trypanosome, but evidence from sequence analyses of several genes places it in the fungal subphylum Taphrinomycotina in the phylum Ascomycota. The Microsporidia were thought to be a unique phylum of protozoa for many years; however, molecular studies have shown that these organisms are fungi. The Microsporidia are obligate intracellular parasites of animals and lack
mitochondria. Most infect
insects, but they are also responsible for common diseases of
crustaceans and
fish and have been found in most other animal groups, including humans (probably transmitted through contaminated food or water).
Hyaloraphidium curvatum was previously classified as a colourless
green alga; however, it has since been recognized as a fungus on the basis of molecular sequence data, which show it to be a member of the order Monoblepharidales in the phylum Chytridiomycota.
Outline of classification of fungi
Since the 1990s, dramatic changes have occurred in the classification of fungi. Improved understanding of relationships of fungi traditionally placed in the phyla Chytridiomycota and Zygomycota has resulted in the dissolution of outmoded taxons and the generation of new taxons. The Chytridiomycota is retained but in a restricted sense. One of Chytridiomycota’s traditional orders, the Blastocladiales, has been raised to phylum status as the Blastocladiomycota. Similarly, the group of anaerobic rumen chytrids, previously known as order Neocallimastigales, has been recognized as a distinct phylum, the Neocallimastigomycota. The phylum Zygomycota is not accepted in the phylogenetic classification of fungi because of remaining doubts about relationships between the groups that have traditionally been placed in this phylum. The consequences of this decision are the recognition of the phylum Glomeromycota and of four subphyla incertae sedis (Latin for “of uncertain position”): Mucoromycotina, Kickxellomycotina, Zoopagomycotina, and Entomophthoromycotina.
The true fungi, which make up the monophyletic clade called kingdom Fungi, comprise seven phyla:
Chytridiomycota, Blastocladiomycota, Neocallimastigomycota,
Microsporidia, Glomeromycota,
Ascomycota, and
Basidiomycota (the latter two being combined in the subkingdom Dikarya). The group of ancestral fungi is thought to be represented by the present-day Chytridiomycota, although the Microsporidia may be an equally ancient sister group. The first major steps in the evolution of higher fungi were the loss of the chytrid flagellum and the development of branching, aseptate fungal filaments, which occurred as terrestrial fungi diverged from water molds 600 million to 800 million years ago. Septate filaments evolved as the Glomeromycota diverged from a combined clade of pre-basidiomycota and pre-ascomycota fungi about 500 million years ago. Hyphae with the characteristic appearance of modern Basidiomycota can be seen in some of the earliest known specimens of plant fossils. Therefore, Ascomycota and Basidiomycota probably diverged as so-called sister groups, which are placed together in subkingdom Dikarya, about 300 million years ago. The easily recognizable
mushroomfungi probably diversified 130 million to 200 million years ago, soon after
flowering plantsbecame an important part of the flora and well before the age of
dinosaurs. A relatively recent evolutionary radiation, perhaps 60 million to 80 million years ago, of anaerobic Chytridiomycota occurred as
grasses and grazing mammals became more abundant; the chytrid fungi serve as symbionts within the rumen of such animals, thereby enabling the grazing mammals to digest grasses.
Classification of the fungi
Distinguishing taxonomic features
The following classification is adapted from
Ainsworth & Bisby’s Dictionary of the Fungi, 10th ed. (2008), and has been amended to adopt the phylogenetic arrangement from the Assembling the Fungal Tree of Life (AFTOL) project funded by the U.S.
National Science Foundation. AFTOL is a work in progress, and uncertainties remain about the exact relationships of many groups. These uncertain groups are indicated in the annotated classification below by the term
incertae sedis, meaning “of uncertain position,” the standard term for a taxonomic group of unknown or undefined relationship. The phylogenetic classification of fungi divides the kingdom into 7 phyla, 10 subphyla, 35 classes, 12 subclasses, and 129 orders.
Annotated classification
-
- Kingdom Fungi
- Eukaryotic (with true nuclei); acellular (e.g., highly adapted parasites), unicellular (e.g., species adapted to life in small volumes of fluid), or multicellular (filamentous) with hyphae; cell walls composed of chitin, polysaccharides (e.g., glucans), or both; can be individually microscopic in size (i.e., yeasts); at least 99,000 species of fungi have been described.
-
- Phylum Chytridiomycota
- Mainly aquatic, some are parasitic or saprotrophic; unicellular or filamentous; chitin and glucan cell wall; primarily asexual reproduction by motile spores (zoospores); mycelia; contains 2 classes.
-
- Class Chytridiomycetes
- Aquatic parasitic (on algae, fungi, or flowering plants) or saprotrophic; unicellular or filamentous; motile cells characterized by a single posterior flagellum; monocentric thallus or polycentric rhizomycelial; contains 3 orders.
-
- Order Chytridiales
- Mainly found in soil; examples of genera include Chytridium, Chytriomyces, and Nowakowskiella.
-
- Order Rhizophydiales
- Aquatic parasitic (on algae) or saprotrophic (in soil or on pollen, keratin, or chitin); sporangia spherical or angular; rhizoids branched; example genus is Rhizophydium.
-
- Order Spizellomycetales
- Parasitic on soil organisms and plants; holocarpic (having all the thallus involved in the formation of the fruiting body) or eucarpic; example genera include Spizellomyces and Powellomyces.
-
- Class Monoblepharidomycetes
- Asexual reproduction by zoospores or autospores; filamentous, branched or unbranched thallus; contains 1 order.
-
- Order Monoblepharidales
- Sexual reproduction by motile gamete (antherozoid) fertilizing nonmotile differentiated egg, resulting in thick-walled oospore; example genus is Monoblepharis.
-
- Phylum Neocallimastigomycota
- Found in digestive tracts of herbivores; anaerobic; zoospores with one or more posterior flagella; lacks mitochondria but contains hydrogenosomes (hydrogen-producing, membrane-bound organelles that generate energy in the form of adenosine triphosphate, or ATP); contains 1 class.
-
- Class Neocallimastigomycetes
- Contains 1 order.
-
- Order Neocallimastigales
- Digest cellulose; example genus is Neocallimastix.
-
- Phylum Blastocladiomycota
- Parasitic on plants and animals, some are saprotrophic; aquatic and terrestrial; flagellated; alternates between haploid and diploid generations (zygotic meiosis); contains 1 class.
-
- Class Blastocladiomycetes
- Parasitic or saprotrophic; contains 1 order.
-
- Order Blastocladiales
- Parasitic (on many different substrates, including decaying fruits) or saprotrophic; example genera include Allomyces and Coelomomyces.
-
- Phylum Microsporidia
- Parasitic on animals and protists; unicellular; highly reduced mitochondria; phylum not subdivided due to lack of well-defined phylogenetic relationships within the group.
-
- Phylum Glomeromycota
- Forms obligate, mutualistic, symbiotic relationships in which hyphae penetrate into the cells of roots of plants and trees (arbuscular mycorrhizal associations); coenocytic hyphae; reproduces asexually; cell walls composed primarily of chitin.
-
- Class Archaeosporomycetes
- Arbuscular mycorrhizal; spores form singly or in loose clusters.
-
- Order Archaeosporales
- Arbuscular mycorrhizal; example genera include Archaeospora and Geosiphon.
-
- Class Glomeromycetes
- Arbuscular mycorrhizal; single or clustered spores; contains 4 orders.
-
- Order Diversisporales
- Arbuscular mycorrhizal; forms complexes of spores; example genera include Acaulospora, Diversispora, and Pacispora.
-
- Order Gigasporales
- Arbuscular mycorrhizal; uses extra-radical auxiliary cells instead of vesicles in plant roots.
-
- Order Glomerales
- Arbuscular mycorrhizal; forms single spores, loose clusters of spores, or compact sporocarps (fruiting bodies); example genus is Glomus.
-
- Class Paraglomeromycetes
- Arbuscular mycorrhizal; forms complexes of spores.
-
- Order Paraglomerales
- Arbuscular mycorrhizal; example genus is Paraglomus.
-
- Subphylum Mucoromycotina (incertae sedis; not assigned to any phylum)
- Parasitic, saprotrophic, or ectomycorrhizal (forms mutual symbiotic associations with plants); asexual or sexual reproduction; branched mycelium; contains 3 orders that represent the traditional Zygomycota.
-
- Order Mucorales (pin molds)
- Parasitic or saprotrophic; filamentous; nonmotile spores (aplanospores); coenocytic mycelium; asexual reproduction by formation of sporangiospores; example genera include Mucor, Parasitella, Phycomyces, Pilobolus, and Rhizopus.
-
- Order Endogonales
- Saprotrophic or mycorrhizal; filamentous; coenocytic mycelium; underground sporocarp; example genera include Endogone, Peridiospora, Sclerogone, and Youngiomyces.
-
- Order Mortierellales
- Parasitic or saprotrophic; fine mycelium, branched (arachnoid); sporangia with 1 or many spores; may form chlamydospores (thick-walled asexual spores); produces garliclike odour; example genera include Mortierella, Dissophora, and Modicella.
-
- Subphylum Entomophthoromycotina (incertae sedis)
- Pathogenic, saprotrophic, or parasitic; coenocytic or septate mycelium; rhizoids formed by some species; conidiophore branched or unbranched; conidia forcibly discharged; contains 1 order.
-
- Order Entomophthorales
- Primarily parasitic on insects, some may be saprotrophic in soil; coenocytic mycelium, may become septate; example genera include Entomophthora, Ballocephala, Conidiobolus, Entomophaga, and Neozygites.
-
- Subphylum Zoopagomycotina (incertae sedis)
- Endoparasitic (lives in the body) or ectoparasitic (lives on the body) on nematodes, protozoa, and fungi; thallus branched or unbranched; asexual and sexual reproduction; contains 1 order.
-
- Order Zoopagales
- Parasitic on amoebas, rotifers, nematodes, and other protozoa; asexual reproduction by conidia borne singly or in chains, not forcibly discharged; example genera include Cochlonema, Rhopalomyces, Piptocephalis, Sigmoideomyces, Syncephalis, and Zoopage.
-
- Subphylum Kickxellomycotina (incertae sedis)
- Saprotrophic, may be parasitic on fungi, can form symbiotic associations; thallus forms from holdfast on other fungi; mycelium branched or unbranched; asexual and sexual reproduction; contains four orders.
-
- Order Kickxellales
- Primarily saprotrophic; mycelium highly branched and occasionally coenocytic; example genera include Kickxella, Coemansia, Linderina, and Spirodactylon.
-
- Order Dimargaritales
- Mycoparasitic; example genera include Dimargaris, Dispira, and Tieghemiomyces.
-
- Order Harpellales
- Endosymbiotic, found in the digestive tracts of insects, including mayflies and stoneflies; thallus simple or branched, septate; asexual reproduction by trichospores; sexual reproduction zygomycetous; example genera include Harpella, Furculomyces, Legeriomyces, and Smittium.
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- Order Asellariales
- Endosymbiotic, found in the digestive tracts of arthropods; thallus branched, septate, attached by basal coenocytic cell; asexual reproduction by arthrospores; example genera include Asellaria and Orchesellaria.
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- Phylum Ascomycota (sac fungi)
- Symbiotic with algae to form lichens, some are parasitic or saprotrophic on plants, animals, or humans; some are unicellular, but most are filamentous; hyphae septate with 1, rarely more, perforation in the septa; cells uninucleate or multinucleate; asexual reproduction by fission, budding, or fragmentation or by conidia that are usually produced on sporiferous (spore-producing) hyphae, the conidiophores, which are borne loosely on somatic (main-body) hyphae or variously assembled in asexual fruiting bodies; sexual reproduction by various means resulting in the production of meiosphores (ascospores) formed by free-cell formation in saclike structures (asci), which are produced naked or, more typically, are assembled in characteristic open or closed bodies (ascocarps, also called ascomata); ascomycota include some cup fungi, saddle fungi, and truffles; this phylum is sometimes included in the subkingdom Dikarya with its sister group, Basidiomycota.
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- Subphylum Taphrinomycotina
- Pathogenic on some plants; unicellular or filamentous; asci produced on the plant surface; ascocarp absent; contains 4 classes.
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- Class Taphrinomycetes
- Parasitic or pathogenic on plants; naked asci; contains 1 order.
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- Order Taphrinales
- Parasitic on plants, causing gall formation; naked asci; example genera include Taphrina and Protomyces.
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- Class Neolectomycetes
- Parasitic or pathogenic on plants; some with large ascocarps; contains 1 order.
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- Order Neolectales
- Parasitic on plant roots; produces large ascocarps; forms yeastlike conidia; example genus is Neolecta.
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- Class Pneumocystidomycetes
- Parasitic or pathogenic in animals; contains 1 order.
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- Order Pneumocystidales
- Parasitic in the alveoli of the lungs of some vertebrates; asexual reproduction by fission; example genus is Pneumocystis.
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- Class Schizosaccharomycetes
- Primarily saprotrophic; groups of fused ascospores may be present; contains 1 order.
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- Order Schizosaccharomycetales (fission yeasts)
- Saprotrophic in fruit juice; asexual reproduction by fission; asci fuse to form groups of 4 or 8 ascospores; example genus is Schizosaccharomyces.
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- Subphylum Saccharomycotina (true yeasts)
- Saprotrophic on plants and animals, including humans, occasionally pathogenic in plants and humans; unicellular; found in short chains; asexual reproduction by budding or fission; contains common yeasts that are relevant to industry (e.g., baking and brewing) and that cause common infections in humans; contains 1 class.
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- Class Saccharomycetes
- Saprotrophic or pathogenic; yeasts reproduce by budding or fission; contains 1 order.
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- Order Saccharomycetales (ascomycete yeasts)
- Saprotrophic or pathogenic in plants and humans; cell walls lack chitin; asci form singly or in chains; example genera include Saccharomyces, Candida, Dipodascopsis, and Metschnikowia.
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- Subphylum Pezizomycotina
- Symbiotic with algae to form lichen; contains all ascomycetes able to produce ascomata; many form ascocarps, although some have lost the ability to undergo meiosis and cannot produce asci (formerly Deuteromycota); contains 10 classes.
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- Class Arthoniomycetes
- Forms lichens; contains 1 order.
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- Order Arthoniales
- Forms lichens; produces asci that elongate to discharge spores; example genera include Arthonia, Dirina, and Roccella.
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- Class Dothideomycetes
- Pathogenic, endophytic, or epiphytic on plants, saprotrophic in soil, parasitic on fungi and animals, or symbiotic with algae to form lichens; spores undergo ascolocular development (in special hyphae pockets); includes subclasses Dothideomycetidae and Pleosporomycetidae; contains 10 orders.
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- Order Capnodiales (sooty molds)
- Grows on honeydew excreted by insects or on exudates on the leaves of plants; melanoid pigments in cell walls of hyphae; included in subclass Dothideomycetidae; example genera include Capnodium, Scorias, and Mycosphaerella.
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- Order Dothideales
- Forms lichens; asci borne in clusters in a locule; included in subclass Dothideomycetidae; example genera include Dothidea, Dothiora, Sydowia, and Stylodothis.
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- Order Hysteriales
- Found on woody branches of trees; stroma is boat-shaped, opening by a longitudinal slit that renders it apothecium-like; asci borne among pseudoparaphyses; example genera include Hysterium and Hysteropatella.
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- Order Jahnulales
- Found in freshwater environments; ascospores covered with sticky gelatin sheaths or apical appendages; hyphae adapted for attaching to wet substrates; example genera include Aliquandostipite, Jahnula, and Patescospora.
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- Order Myriangiales
- Parasitic on fungi and insects, epiphytic on leaves and stems; found mostly in tropical or subtropical regions; ascocarp present; asci borne singly in locules arranged at various levels in a globose stroma; included in subclass Dothideomycetidae; example genera include Myriangium and Elsinoe.
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- Order Pleosporales
- Forms lichens, some are pathogenic on plants; asci borne in a basal layer among pseudoparaphyses; included in subclass Pleosporomycetidae; example genera include Pleospora, Phaeosphaeria, Lophiostoma, Sporormiella, and Helminthosporium.
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- Order Botryosphaeriales (incertae sedis; not placed in any subclass)
- Pathogenic and endophytic in plants; ascospores are forcibly discharged; example genera include Botryosphaeria and Guignardia.
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- Order Microthyriales (incertae sedis; not placed in any subclass)
- Saprotrophic or epiphytic on stems and leaves.
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- Order Patellariales (incertae sedis; not placed in any subclass)
- Parasitic and saprotrophic; flask-shaped (perithecium-like) fruiting bodies; example genus is Patellaria.
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- Order Trypetheliales (incertae sedis; not placed in any subclass)
- Forms lichen; most have hyaline ascospores.
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- Class Eurotiomycetes
- Parasitic on animals, saprotrophic in soil; small, evanescent asci, found at various levels within spherical ascocarp; includes subclasses Chaetothyriomycetidae, Eurotiomycetidae, and Mycocaliciomycetidae; contains 7 orders.
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- Order Chaetothyriales
- Pathogenic in humans or saprotrophic on plants; ascocarps contain sterile filaments on the reproductive organs; included in subclass Chaetothyriomycetidae; example genera include Capronia, Ceramothyrium, and Chaetothyrium.
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- Order Pyrenulales
- Parasitic, saprotrophic, or symbiotic with algae to form lichens; asci evanescent; ascospores may be pigmented; included in subclass Chaetothyriomycetidae; example genera include Pyrenula and Pyrgillus.
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- Order Verrucariales
- Forms lichens on rocks and other substrates; perithecia (closed ascocarps with a pore in the top) have small depression-like spots on the surface; included in subclass Chaetothyriomycetidae; example genera include Agonimia, Dermatocarpon, Polyblastia, and Verrucaria.
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- Order Coryneliales
- Forms lichens; asci in ascostromata with funnel-shaped ostioles at maturity; included in subclass Eurotiomycetidae; examples of genera include Corynelia and Caliciopsis.
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- Order Eurotiales
- Parasitic in animals, saprotrophic in soil; asci evanescent; included in subclass Eurotiomycetidae; examples of genera include Eurotium, Penicillium, Talaromyces, Elaphomyces, Trichocoma, and Byssochlamys.
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- Order Onygenales
- Forms lichens; asci are formed in a mazaedium (a fruiting body consisting of a powdery mass of free spores interspersed with sterile threads, enclosed in a peridium or wall structure) and are evanescent; included in subclass Eurotiomycetidae; examples of genera include Onygena, Gymnoascus, Trichophyton, and Arthroderma.
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- Order Mycocaliciales
- Saprotrophic on lichens; includes nonlichenized calicioid fungi; ascomata stalked or sessile; included in subclass Mycocaliciomycetidae; examples of genera include Mycocalicium, Chaenothecopsis, Stenocybe, and Sphinctrina.
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- Class Laboulbeniomycetes
- Primarily parasitic on insects; contains 2 orders.
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- Order Laboulbeniales
- Parasitic on insects, including the true flies (order Diptera); ascospore attaches to and penetrates insect exoskeleton to absorb nutrients; spinelike ascoma; example genera include Laboulbenia, Rickia, and Ceratomyces.
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- Order Pyxidiophorales
- Ectoparasitic on mandibulate arthropods, may be mycoparasitic; mycelial; anamorphs lack vesiculate conidiophores; example genus includes Pyxidiophora.
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- Class Lecanoromycetes
- Forms lichens; thick ascal apex with narrow canal; includes subclasses Acarosporomycetidae, Lecanoromycetidae, and Ostropomycetidae; contains 10 orders.
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- Order Acarosporales
- Forms lichens; asci unitunicate and lecanoralean (resembling asci of the genus Lecanora), with nonamyloid or slightly amyloid inner ascus apex (tholus); included in subclass Acarosporomycetidae; example genera include Acarospora, Pleopsidium, and Sarcogyne.
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- Order Lecanorales
- Forms lichens; apothecia fruiting bodies; includes reindeer mosses, cup lichens, and beard lichens; included in subclass Lecanoromycetidae; example genera include Cladonia, Lecanora, Parmelia, Ramalina, and Usnea.
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- Order Peltigerales
- Forms lichens; thallus may be large and lobate; apothecia may be lecanorine or lecideine (darkened margin sometimes lacking a thalline margin); includes dog lichens; included in subclass Lecanoromycetidae; example genera include Coccocarpia, Collema, Nephroma, Pannaria, and Peltigera.
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- Order Teloschistales
- Forms lichens; found on rocks close to the sea; thallus sometimes composed of granules; may have poorly defined lobed margins; includes orange sea lichen and shore lichen (yellow scales); included in subclass Lecanoromycetidae; example genera include Caloplaca, Teloschistes, and Xanthoria.
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- Order Agyriales
- Forms lichens; thallus may be nonlobate; includes bullseye lichen and disk lichen; included in subclass Ostropomycetidae; examples of genera include Agyrium, Placopsis, Trapelia, and Trapeliopsis.
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- Order Baeomycetales
- Forms lichens; stalked or sessile ascomata; includes cap lichen; included in subclass Ostropomycetidae; example genus includes Baeomyces.
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- Order Ostropales
- Forms lichens; apothecia may be capitate-stipitate or sessile turbinate; includes dimple lichen, gomphillus lichen, and common script lichen; included in subclass Ostropomycetidae; examples of genera include Ostropa, Stictis, Gyalecta, Gomphillus, Graphis, Odontotrema, Porina, and Thelotrema.
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- Order Umbilicariales
- Forms lichens; grows on rocks; thallus is often foliose and is attached to substrate by an umbilicus; includes rock tripe; examples of genera include Lasallia and Umbilicaria.
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- Order Pertusariales
- Forms lichens; grows on rocks, mosses, and barks; primary thallus may be crustose, squamulose, or foliose; clustered or solitary apothecia; ascospores may be colourless; ascocarps may be absent; includes peppermint drop lichen; included in subclass Ostropomycetidae; examples of genera include Coccotrema, Icmadophila, Ochrolechia, and Pertusaria.
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- Order Candelariales (incertae sedis; not placed in any subclass)
- Forms lichens; commonly grows on rocks and shrubs; thallus is yellow to orange in colour; most are nitrophilus; apothecia may be lecanorine; thallus may be foliose; example genera include Candelaria and Candelariella.
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- Class Leotiomycetes
- Parasitic on plants, especially fruits; thin-walled, inoperculate asci, generally with amyloid apical rings; includes mildews; contains 5 orders.
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- Order Cyttariales
- Parasitic on plants, causes gall formation, especially on beech trees; spherical, dimpled ascocarps that are yellow to orange in colour; example genus includes Cyttaria.
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- Order Erysiphales (powdery mildews)
- Parasitic on plants; ascospores or conidia germinate on leaves and stems; mycelium septate, branched; example genera include Erysiphe, Blumeria, and Uncinula.
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- Order Helotiales
- Pathogenic on plants, saprotrophic, endophytic, mycorhizzal, mycoparasitic, or symbiotic on roots; inoperculate asci with distinct hymenium; apothecia disk-shaped to goblet-shaped; example genera include Dactylella, Hymenoscyphus, and Ascocoryne.
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- Order Rhytismatales
- Pathogenic on plants; asci have apical rings; ascomata develop in host tissue; ascospores long and thin; includes tar spot fungi; example genera include Rhytisma, Lophodermium, and Cudonia
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- Order Thelebolales
- Coprophilus (grows on dung); ascomata small, disk-shaped to globose; may have polysporus asci; example genera include Thelebolus, Coprotus, and Ascozonus.
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- Class Lichinomycetes
- Parasitic, saprotrophic, or symbiotic; inoperculate asci; includes peltula lichen; contains 1 order.
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- Order Lichinales
- Forms lichens; asci may be lecanoralean or prototunicate; example genera include Heppia, Lichina, and Peltula.
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- Class Orbiliomycetes
- Parasitic or saprotrophic, with many found on bark; includes some cup fungi; contains 1 order.
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- Order Orbiliales
- Parasitic on nematodes, non-lichen-forming; inoperculate ascus, may bifurcate and have a flexible stalk and truncated apex; example genera include Orbilia and Hyalorbilia.
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- Class Pezizomycetes
- Saprotrophic on wood, soil, or dung; unitunicate, operculate asci; includes some cup fungi; contains 1 order.
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- Order Pezizales
- Saprotrophic; amyloid asci; ascomata nonstalked, may be goblet-shaped or saucer-shaped; ascocarp may be operculate aboveground or be borne belowground; includes truffles; example genera include Peziza, Glaziella, Morchella, Pyronema, Terfezia, and Tuber.
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- Class Sordariomycetes
- Pathogenic on plants, causing canker formation, some are saprotrophic; ascomata typically perithecial with prominent ostioles and may be pear-shaped to globose; includes subclasses Hypocreomycetidae, Sordariomycetidae, and Xylariomycetidae; contains 19 orders.
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- Order Coronophorales
- Saprotrophic on wood; asci in ascostromata with irregular or round openings; ascomata sometimes covered with hairs (filaments); included in subclass Hypocreomycetidae; example genera include Nitschkia, Scortechinia, Bertia, and Chaetosphaerella.
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- Order Hypocreales
- Parasitic or pathogenic on plants, may cause canker formation; when present, perithecia and stromata are brightly coloured, soft, fleshy, or waxy; asci borne in a basal layer among apical paraphyses; included in subclass Hypocreomycetidae; example genera include Hypocrea, Nectria, Cordyceps, Claviceps, and Niesslia.
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- Order Melanosporales
- Mycoparasitic or saprotrophic; asci evanescent and unitunicate; perithecial or cleistothecial ascomata; included in subclass Hypocreomycetidae; example genus is Melanospora.
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- Order Microascales
- Parasitic on plants; asci evanescent (quickly deteriorating), borne at different levels in perithecia with ostioles, or sometimes with a long necklike structure terminating in a pore; included in subclass Hypocreomycetidae; example genera include Microascus, Petriella, Halosphaeria, Lignincola, and Nimbospora.
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- Order Boliniales
- Saprotrophic; ascocarp may be black and shiny; some with irregular stromata; included in subclass Sordariomycetidae; examples of genera include Camarops and Apiocamarops.
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- Order Calosphaeriales
- Saprotrophic; ascospores small; included in subclass Sordariomycetidae; examples of genera include Calosphaeria, Togniniella, and Pleurostoma.
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- Order Chaetosphaeriales
- Saprotrophic; ascomata subglobose to globose; paraphyses sparse to abundant; asci unitunicate, may lack apical ring; included in subclass Sordariomycetidae; examples of genera include Chaetosphaeria, Melanochaeta, Zignoëlla, and Striatosphaeria.
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- Order Coniochaetales
- Saprotrophic; ascomata subglobose to globose; filiform paraphyses; asci unitunicate; included in subclass Sordariomycetidae; examples of genera include Coniochaeta and Coniochaetidium.
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- Order Diaporthales
- Pathogenic on plants, causing chestnut blight, root rot, and black spot; paraphyses absent; asci free within ascomata; included in subclass Sordariomycetidae; examples of genera include Diaporthe, Gnomonia, Cryphonectria, and Valsa.
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- Order Ophiostomatales
- Pathogenic on plants, causing diseases such as Dutch elm disease and oak wilt; long, tubular ascomata with ostiole at the tip, through which spores are released; included in subclass Sordariomycetidae; examples of genera include Ophiostomaand Fragosphaeria.
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- Order Sordariales
- Mainly saprotrophic in soil and dung; ascomata solitary and perithecial; includes species commonly used in genetics research; included in subclass Sordariomycetidae; examples of genera include Sordaria, Podospora, Neurospora, Lasiosphaeria, and Chaetomium.
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- Order Xylariales
- Saprotrophic; inoperculate asci; some with white conidia; included in subclass Xylariomycetidae; examples of genera include Xylaria, Hypoxylon, Anthostomella, Diatrype, and Graphostroma.
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- Order Lulworthiales (incertae sedis; not placed in any subclass)
- Saprotrophic; ascomata subglobose to pear-shaped, paraphyses absent; asci unitunicate, thin-walled; example genera include Lulworthia and Lindra.
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- Order Meliolales (incertae sedis; not placed in any subclass)
- Lives on other organisms (biotrophic) in tropical regions; mycelium dark, superficial, typically bearing appendages (hyphopodia or setae); asci in basal layers in ostiolate perithecia without appendages; example genus includes Meliola.
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- Order Phyllachorales (incertae sedis; not placed in any subclass)
- Parasitic on plants and saprotrophic on salt marsh plants; some produce perithecia shielded inside a stroma, others do not produce a stroma; example genus is Phyllachora.
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- Order Trichosphaeriales (incertae sedis; not placed in any subclass)
- Pathogenic on plants, saprotrophic on wood; ascomata globose, dark, and superficial; cylindrical, stalked asci; some produce muriform (brick-shaped) spores; example genus is Trichosphaeria.
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- Pezizomycotina (incertae sedis; not placed in any class)
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- Order Lahmiales
- Pathogenic on trees, mainly aspens; example genus is Lahmia.
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- Order Medeolariales
- Saprotrophic; example genus is Medeolaria.
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- Order Triblidiales
- Saprotrophic; ascomata solitary or clustered; example genera include Huangshania, Pseudographis, and Triblidium.
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- Phylum Basidiomycota
- Parasitic or saprotrophic on plants or insects; filamentous; hyphae septate, with septa typically inflated (dolipore) and centrally perforated; mycelium of two types: primary consisting of uninucleate cells, succeeded by secondary consisting of dikaryotic cells, often bearing bridgelike clamp connections over the septa; asexual reproduction by fragmentation, oidia(thin-walled, free, hyphal cells behaving as spores), or conidia; sexual reproduction by fusion of hyphae (somatogamy), fusion of an oidium with a hypha (oidization), or fusion of a spermatium (a nonmotile male structure that empties its contents into a receptive female structure during plasmogamy) with a specialized receptive hypha (spermatization), resulting in dikaryotic hyphae that eventually give rise to basidia, either singly on the hyphae or in variously shaped basidiocarps (also called basidiomata); meiospores (basidiospores) borne on basidia; in the rusts and smuts, the dikaryotic hyphae produce teleutospores (thick-walled resting spores), which are a part of the basidial apparatus; this is a large phylum of fungi containing the rusts, smuts, jelly fungi, club fungi, coral and shelf fungi, mushrooms, puffballs, stinkhorns, and bird’s-nest fungi; sometimes included in the subkingdom Dikarya with its sister group, Ascomycota.
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- Subphylum Pucciniomycotina
- Pathogens of land plants; includes the rusts; contains eight classes.
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- Class Pucciniomycotina
- Parasitic on plants, some saprotrophic; contains 5 orders.
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- Order Septobasidiales
- Parasitic on plants, some members parasitic on or symbiotic with scale insects (order Homoptera); basidiospores germinate on insects, with haustoria coiled inside insect; example genera include Septobasidium and Auriculoscypha.
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- Order Pachnocybales
- Parasitic on plants; uninucleate basidiospores; singular conidia; hyphal cell wall ruptures during branching; example genus includes Pachnocybe.
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- Order Helicobasidiales
- Mycoparasitic; violet-coloured mycelia release powdery conidia when emerging; example genera include Helicobasidiumand Tuberculina.
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- Order Platygloeales
- Parasitic on mosses and other plants; pycnium (fruiting body of rusts) forms masses of hyphae inside mosses; example genera include Platygloea and Eocronartium.
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- Order Pucciniales
- Parasitic on plants; typically have 5 spore stages and 2 alternate hosts; example genera include Puccinia and Uromyces.
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- Class Cystobasidiomycetes
- Parasitic on plants; simple-septate basidiomycetes; contains 3 orders.
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- Order Cystobasidiales
- Parasitic on plants; yeasts are non-teliospore-forming and produce auricularioid basidia and ballistospores (spores that are forcibly discharged); example genera include Cystobasidium, Occultifur, and Rhodotorula.
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- Order Erythrobasidiales
- Some are pathogenic in humans and animals, others are saprotrophic in soil or found in the air; yeastlike cells may be spherical or elongate; example genera include Erythrobasidium, Sporobolomyces, and Bannoa.
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- Order Naohideales
- Mycoparasitic; auricularoid basidia may contain mitospores; example genus is Naohidea.
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- Class Agaricostilbomycetes
- Parasitic or saprotrophic; simple-septate basidiomycetes; contains 2 orders.
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- Order Agaricostilbales
- Mostly saprotrophic; fruiting body is septate, with uniform hyphae; some have slender basidiospores, which may germinate by budding and may be solitary or clustered; example genera include Agaricostilbum and Chionosphaera.
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- Order Spiculogloeales
- Parasitic or saprotrophic; spinulose to granulose auricularoid basidia; include jelly fungi; example genera include Mycogloea and Spiculogloea.
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- Class Microbotryomycetes
- Pathogenic in plants, some are mycoparasitic; includes some yeasts; contains 4 orders.
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- Order Heterogastridiales
- Mycoparasitic; basidiocarps may be pycnidioid; example genus includes Heterogastridium.
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- Order Microbotryales
- Pathogenic in plants (some cause smut); violet teliospores; example genera include Microbotryum and Ustilentyloma.
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- Order Leucosporidiales
- Mycoparasitic; mycelia lack clamp connections; septate basidia; example genera include Leucosporidiella, Leucosporidium, and Mastigobasidium.
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- Order Sporidiales
- Nonpathogenic; basidia may be very long; hyphae with clamp connections; some species emit peachlike odour; example genera include Sporidiobolus and Rhodosporidium.
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- Class Atractiellomycetes
- Parasitic or saprotrophic; simple septate; some pycnidial members; auricularoid basidia; gastroid; contains 1 order.
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- Order Atractiellales
- Parasitic or saprotrophic; minute globuse conidia formed from tips of hyphae; example genera include Atractiella, Saccoblastia, Helicogloea, and Phleogena.
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- Class Classiculomycetes
- Parasitic; uredinalian septal pores with tremelloid haustorial cells; contains 1 order.
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- Order Classiculales
- Saprotrophic; many are aquatic or aeroaquatic hyphomycetes; simple septal pores; some with long fusiform basidiospores; example genera include Classicula and Jaculispora.
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- Class Mixiomycetes
- Parasitic or saprotrophic; simple septate; contains 1 order.
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- Order Mixiales
- Parasitic primarily on ferns; blastosporic yeasts; example genus is Mixia.
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- Class Cryptomycocolacomycetes
- Parasitic; simple septate; contains 1 order.
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- Order Cryptomycocolacales
- Parasitic on insects such as bark beetles, some are mycoparasitic; sometimes fuse with host cells using a small pore in colacosome; example genera include Cryptomycocolax and Colacosiphon.
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- Subphylum Ustilaginomycotina
- Parasitic on plants as dikaryotic hyphae; haploid yeast phase is saprotrophic; contains 2 classes.
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- Class Ustilaginomycetes
- Parasitic (dikaryotic phase) and saprotrophic (haploid phase); includes smut fungi; contains 3 orders.
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- Order Urocystales
- Parasitic on plants such as arrowhead, causing blister smut, and wheat, causing flag smut; mycelia may form dense clusters in leaves and leaf stalks (petioles); example genera include Urocystis, Ustacystis, and Doassansiopsis.
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- Order Ustilaginales
- Parasitic on plants, causing smut of many cereal grains, including wheat, barley, corn, and rice; masses of spores (sori) are usually black and dusty; basidial apparatus consisting of thick-walled teleutospore (probasidium), which upon germination gives rise to a septate or nonseptate tube (metabasidium) bearing basidiospores; basidiospores not forcibly discharged, germinating usually by budding or by fusing and then producing a mycelial germ tube; example genera include Ustilago and Cintractia.
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- Class Exobasidiomycetes
- Parasitic and pathogenic on plants; includes smut fungi; contains 7 orders.
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- Order Doassansiales
- Parasitic on plants; holobasidia (single-celled, may be club-shaped); teliosporic; example genera include Doassansia, Rhamphospora, and Nannfeldtiomyces.
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- Order Entylomatales
- Parasitic and pathogenic on plants, causing rice leaf smut and dahlia smut; ballistospore-forming; example genera include Entyloma and Tilletiopsis.
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- Order Exobasidiales
- Parasitic and pathogenic on vascular plants; lacking basidiocarps; basidia produced in a layer on the surface of parasitized plants; example genera include Exobasidium, Clinoconidium, and Dicellomyces.
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- Order Georgefischeriales
- Parasitic on plants; holobasidia; may reproduce sexually in teleomorphic phase; example genera include Georgefischeria, Phragmotaenium, Tilletiaria, and Tilletiopsis.
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- Order Malasseziales
- Symbiotic on skin of animals but can become pathogenic, mainly affecting dogs and cats; asexual; rapidly budding yeasts with thick cell walls, colonies range in colour from cream to yellow, brown, or orange; conidia are globose to elliptical-shaped; example genus is Malassezia.
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- Order Microstromatales
- Parasitic on plants, some found in the nectar of orchids; some are nonteliosporic; some are anamorphic yeasts lacking septal pores; example genera include Microstroma, Sympodiomycopsis, and Volvocisporium.
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- Order Tilletiales
- Parasitic on grasses (family Poaceae); ballistospore-forming; primary basidiospores may conjugate, forming dikaryon capable of infecting hosts; example genera include Tilletia, Conidiosporomyces, and Erratomyces.
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- Subphylum Agaricomycotina
- Parasitic or symbiotic on plants, animals, and other fungi, some are saprotrophic or mycorrhizal; basidia may be undivided or have transverse or longitudinal septa; dolipore (inflated) septa and septal pore cap (parenthesomes) present; includes mushrooms, bracket fungi, puffballs; contains 3 classes.
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- Class Tremellomycetes
- Parasitic or saprotrophic; if present, parenthesome separated into cup-shaped sections; gelatinous fruiting bodies may be absent; includes 3 orders.
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- Order Cystofilobasidiales
- Parasitic and pathogenic on plants (causing black canker of parsnips), may be saprotrophic; dolipores present; may lack parenthesomes; unicellular yeasts; example genera include Cystofilobasidium, Mrakia, and Itersonilia.
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- Order Filobasidiales
- Pathogenic in humans, causing cryptococcosis, parasitic on fungi, insects, and humans, saprotrophic in soil and dung; mitosporic; asexual reproduction as yeasts, which are encapsulated, with colonies ranging in colour from cream to pink, yellow, or brown; sexual reproduction as teleomorph; example genera include Filobasidiella and Cryptococcus.
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- Order Tremellales
- Parasitic on mosses, vascular plants, or insects, although most are saprotrophic; basidiocarps well-formed, appearing as inconspicuous horny crusts when dry but usually bright-coloured to black gelatinous masses after a rain; example genera include Tremella, Trichosporon, and Christiansenia.
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- Class Dacrymycetes
- Mostly saprotrophic; parenthesome imperforate (forms a dome-shaped cover over dolipore); contains 1 order.
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- Order Dacrymycetales
- Saprotrophic; some with “tuning fork” basidia; some with fruiting bodies ranging from cup-shaped to cone-shaped; example genera include Dacrymyces, Calocera, and Guepiniopsis.
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- Class Agaricomycetes
- Parasitic, pathogenic, symbiotic, or saprotrophic; most are terrestrial, with few aquatic members; all are mushroom-forming; parenthesomes imperforate or perforate (spore cap has openings); includes subclasses Agaricomycetidae and Phallomycetidae; contains 17 orders.
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- Order Agaricales
- Most are saprotrophic, some are parasitic on plants (causing root rot), others are mycorrhizal; basidia produced in layers (hymenia) on the underside of fleshy fruiting bodies (basidiocarps), in tubes (boletes), or on gills (mushrooms); includes inky cap mushrooms and some species of earthstars and puffballs in the family Lycoperdaceae; included in subclass Agaricomycetidae; example genera include Agaricus, Armillaria, Coprinus, and Pleurotus.
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- Order Atheliales
- Mycorrhizal, found primarily on conifers and hardwood trees; included in subclass Agaricomycetidae; example genera include Athelia, Piloderma, and Tylospora.
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- Order Boletales
- Saprotrophic, many are found living at the base of trees such as pines; spores enclosed in fruiting body, become dusty at maturity and are expelled into the air; includes some edible boletes, such as butter boletes, king boletes, and queen boletes, as well as pigskin poison puffballs; included in subclass Agaricomycetidae; example genera include Boletus, Scleroderma, Coniophora, and Rhizopogon.
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- Order Geastrales
- Found under trees, mainly conifers; spherical or egg-shaped fruiting bodies resemble mushrooms, some become star-shaped after splitting open to release spores; includes earthstars; included in subclass Phallomycetidae; example genera include Geastrum, Radiigera, and Sphaerobolus.
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- Order Gomphales
- Most are mycorrhizal, some are saprotrophic; spores may be olive-shaped, usually rough; included in subclass Phallomycetidae; example genera include Gomphus, Gautieria, and Ramaria.
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- Order Hysterangiales
- Most are saprotrophic; resembles puffballs when small, becoming pear-shaped and finally globose when mature; fruiting body may be pink to vibrant lilac in colour; mature internal tissue characterized by fetid odour; includes club-shaped stinkhorn; included in subclass Phallomycetidae; example genera include Hysterangium, Phallogaster, Gallacea, and Austrogautieria.
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- Order Phallales
- Found in temperate zones; phalluslike fruiting body with fetid odour, often slimy; includes stinkhorns; included in subclass Phallomycetidae; example genera include Phallus, Clathrus, and Claustula.
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- Order Auriculariales (incertae sedis; not placed in any subclass)
- Saprotrophic; basidia may be divided longitudinally; gelatinous fruiting body may appear to be upside-down and may fuse to form large masses; includes ear fungus and black jelly roll; example genera include Auricularia, Exidia, and Bourdotia.
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- Order Cantharellales (incertae sedis; not placed in any subclass)
- Saprotrophic; basidia have unusual shapes; hyphae may be thin-walled or thick-walled, with or without clamp connections; example genera include Cantharellus, Botryobasidium, Craterellus, and Tulasnella.
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- Order Corticiales (incertae sedis; not placed in any subclass)
- Parasitic, saprotrophic, or symbiotic with algae to form lichen; spores range in colour from white to pink; hyphae clamped; example genera include Corticium, Vuilleminia, and Punctularia.
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- Order Gloeophyllales (incertae sedis; not placed in any subclass)
- Saprotrophic; many cause wood rot; basidiospores may be cylindrical to ellipsoidal in shape; hyphae clamped; example genera include Gloeophyllum, Neolentinus, and Veluticeps.
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- Order Hymenochaetales (incertae sedis; not placed in any subclass)
- Mycorrhizal or saprotrophic; many cause white rot; fruiting body may be inconspicuous; many with imperforate parenthesome; example genera include Hymenochaete, Phellinus, and Trichaptum.
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- Order Polyporales (incertae sedis; not placed in any subclass)
- Mycorrhizal or saprotrophic, often found on decaying wood; basidia borne in various ways but rarely on gills; fruiting body may be mushroomlike; example genera include Polyporus, Fomitopsis, and Phanerochaete.
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- Order Russulales (incertae sedis; not placed in any subclass)
- Parasitic or saprotrophic, often found at the base of trees; fruiting body may be slimy; many have gills; some are very large, reaching a diameter of 1 metre (3.3 feet); includes some edible fungi, such as some species of tooth fungi; example genera include Russula, Aleurodiscus, Bondarzewia, Hericium, Peniophora, and Stereum.
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- Order Sebacinales (incertae sedis; not placed in any subclass)
- Symbiotic with plants, some form mycorrhizal associations; forms hyphal networks on and within roots; chlamydospores generated inside root cells or at root surface; example genera include Sebacina, Tremellodendron, and Piriformospora.
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- Order Thelephorales (incertae sedis; not placed in any subclass)
- Found in the ground in wooded areas; fruiting bodies black to brown; hyphae usually have clamp connections; example genera include Thelephora, Bankera, and Polyozellus.
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- Order Trechisporales (incertae sedis; not placed in any subclass)
- Found on wood or in soil; clavate (club-shaped) or stipitate (stalk-shaped) basidiomata; hyphae with clamp connections; example genera include Trechispora, Sistotremastrum, and Porpomyces.
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- Basidiomycota (incertae sedis)
- Includes basidiomycota not placed in a subphylum; contains 2 classes.
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- Class Wallemiomycetes
- Includes molds that are pathogenic in humans; osmophilic (capable of living on surfaces with highly concentrated solutes, such as salt or sugar); contains 1 order.
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- Order Wallemiales
- Pathogenic in humans, contains known allergens; found in soil, hay, and textiles; spores are typically brown in colour and formed in chains; example genus is Wallemia.
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- Class Entorrhizomycetes
- Pathogenic or saprotrophic on roots of plants; contains 1 order.
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- Order Entorrhizales
- Pathogenic or saprotrophic; hyphae clamped; dolipore and parenthesome present; contains the only smut fungus that causes gall formation on roots; example genus is Entorrhiza.
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- Kingdom Chromista
- Common microorganisms; includes important plant pathogens, such as the cause of potato blight (Phytophthora); motile spores swim by means of 2 flagella and grow as hyphae with cellulose-containing walls; includes the majority of the Oomycota; contains a total of approximately 110 genera and 900 species.
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- Phylum Hyphochytriomycota
- Microscopic organisms that are parasitic or saprotrophic on algae and fungi in fresh water and in soil; forms a small thallus, often with branched rhizoids; whole of the thallus is eventually converted into a reproductive structure; contains 23 species in 6 genera.
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- Order Hyphochytriales
- Mostly marine; motile cells bear a single tinsel flagellum (a flagellum with short side branches along the central axis, comblike); example genera include Hyphochytrium and Rhizidiomyces.
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- Phylum Labyrinthulomycota
- Found in both salt water and fresh water in association with algae and other chromists; feeding stage comprises an ectoplasmic network and spindle-shaped or spherical cells that move within the network by gliding over one another; contains about 45 species in 10 genera.
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- Order Labyrinthulales
- Parasitic on marine algae, symbiotic with algae or vascular plants, parasitic on plants, or saprotrophic in soil; motile cells glide on an extracellular matrix secreted by an organelle known as a sagenogenetosome; example genus is Labyrinthula.
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- Order Thraustochytriales
- Found in fresh water and salt water, as well as in saline soil; secrete ectoplasmic nets from a sagenogenetosome; monocentric thallus; example genus is Thraustochytrium.
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- Phylum Oomycota
- Found in fresh water, wet soil, and marine habitats, some are pathogenic (such as Saprolegnia and Phytophthora); contains about 600 species in 90 genera.
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- Order Leptomitales
- Aquatic, saprotrophic, often found in polluted water; eucarpic; hyphae constricted, with cellulin plugs, arising from a well-defined basal cell; oogonium typically containing a single egg, which may be free or embedded in periplasm (a peripheral layer of protoplasm); example genera include Apodachlyella, Ducellieria, Leptolegniella, and Leptomitus.
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- Order Myzocytiopsidales
- Pathogenic in insects of the order Diptera; spores develop within a sporangium; example genus is Crypticola.
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- Order Olpidiopsidales
- Pathogenic on marine plants, including laver (nori); thallus infects cells of host; example genus is Olpidiopsis.
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- Order Peronosporales
- Aquatic or terrestrial; parasitic on algae or vascular plants, the latter mostly obligate parasites causing downy mildews; in advanced species, zoosporangia borne on well-differentiated sporangiophores, deciduous and behaving as conidia (asexually produced spores); example genera include Albugo, Peronospora, Bremia, and Plasmopara.
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- Order Pythiales
- Pathogenic in plants, algae, and fungi, some are saprotrophic in soil or water; hyphae may grow within or between cells of plants, causing root rot; example genera include Pythium, Phytophthora, and Pythiogeton.
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- Order Rhipidiales
- Aquatic, saprotrophic, often found in polluted waters; thallus contains cellulin plugs, usually branched and inflated; example genus is Rhipidium.
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- Order Salilagenidiales
- Marine, parasitic on prawns and lobsters; mycelia penetrate exoskeleton; example genus is Haliphthoros.
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- Order Saprolegniales (water molds)
- Parasitic or saprotrophic; some cause root rot, others infect fish and fish eggs; mostly eucarpic, filamentous water molds or soil fungi; hyphae without constrictions or cellulin plugs; oogonia containing 1 to many eggs; some species are diplanetic, producing 2 types of zoospores (primary pear-shaped spores with anterior flagella and secondary kidney-shaped spores with lateral flagella); example genera include Leptolegnia, Achlya, and Saprolegnia.
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- Order Sclerosporales
- Parasitic on plants, causing root rot; can survive in soil for long periods of time; thick-walled oogonia; may lack haustoria; example genera include Sclerospora and Verrucalvus.
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- Order Anisolpidiales
- Found in marine environments, parasitic; example genus is Anisolpidium.
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- Order Lagenismatales
- Found in marine environments, parasitic; filamentous; example genus is Lagenisma.
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- Order Rozellopsidales
- Found in marine environments, parasitic on euglena, some are biotrophic with other Oomycota or algae; may have naked thalli; example genera include Pseudosphaerita and Rozellopsis.
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- Order Haptoglossales
- Parasitic on algae or plant roots, including roots of sugar beets; may be non-mycelial-forming; sporangia develop inside host cells; example genera include Haptoglossa, Lagena, and Pontisma.
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