Ascomycota is a division or phylum of the kingdom
Fungi that, together
with the Basidiomycota, form the subkingdom Dikarya. Its members are
commonly known as the sac fungi or ascomycetes. They are the largest
phylum of Fungi, with over 64,000 species. The defining feature of
this fungal group is the "ascus" (from Greek: ἀσκός (askos),
meaning "sac" or "wineskin"), a microscopic sexual structure in which
nonmotile spores, called ascospores, are formed. However, some species
Ascomycota are asexual, meaning that they do not have a sexual
cycle and thus do not form asci or ascospores. Previously placed in
Deuteromycota along with asexual species from other fungal taxa,
asexual (or anamorphic) ascomycetes are now identified and classified
based on morphological or physiological similarities to ascus-bearing
taxa, and by phylogenetic analyses of
The ascomycetes are a monophyletic group, i.e. it contains all
descendants of one common ancestor. This group is of particular
relevance to humans as sources for medicinally important compounds,
such as antibiotics and for making bread, alcoholic beverages, and
cheese, but also as pathogens of humans and plants. Familiar examples
of sac fungi include morels, truffles, brewer's yeast and baker's
yeast, dead man's fingers, and cup fungi. The fungal symbionts in the
majority of lichens (loosely termed "ascolichens") such as Cladonia
belong to the Ascomycota. There are many plant-pathogenic ascomycetes,
including apple scab, rice blast, the ergot fungi, black knot, and the
powdery mildews. Several species of ascomycetes are biological model
organisms in laboratory research. Most famously, Neurospora crassa,
several species of yeasts, and
Aspergillus species are used in many
genetics and cell biology studies.
Penicillium species on cheeses and
those producing antibiotics for treating bacterial infectious diseases
are examples of taxa that belong to the Ascomycota.
1 Asexual reproduction in ascomycetes and their characteristics
2 Modern classification of Ascomycota
3 Outdated taxon names
6 Distribution and living environment
7.1 Asexual reproduction
7.1.1 Asexual spores
7.1.2 Conidiogenesis and dehiscence
7.2 Heterokaryosis and parasexuality
7.3 Sexual reproduction
7.3.1 Formation of sexual spores
8.2 Mycorrhizal fungi and endophytes
8.3 Symbiotic relationships with animals
9 Importance for humans
9.1 Harmful interactions
9.2 Positive effects
10 See also
12 Cited texts
Asexual reproduction in ascomycetes and their characteristics
Ascomycetes are 'spore shooters'. They are fungi which produce
microscopic spores inside special, elongated cells or sacs, known as
'asci', which give the group its name.
Asexual reproduction is the dominant form of propagation in the
Ascomycota, and is responsible for the rapid spread of these fungi
into new areas. Asexual reproduction of ascomycetes is very diverse
from both structural and functional points of view. The most important
and general is production of conidia, but chlamydospores are also
frequently produced. Furthermore,
Ascomycota also reproduce asexually
1) Conidia formation:
Asexual reproduction may occur through vegetative reproductive spores,
the conidia. Asexual, non-motile haploid spore of a fungus, which is
named after the Greek word for dust; conia and hence also known as
conidiospores and mitospores. The conidiospores commonly contain one
nucleus and are products of mitotic cell divisions and thus are
sometimes call mitospores, which are genetically identical to the
mycelium from which they originate. They are typically formed at the
ends of specialized hyphae, the conidiophores. Depending on the
species they may be dispersed by wind or water, or by animals.
Conidiophores may simply branch off from the mycelia or they may be
formed in fruiting bodies.
The hypha that creates the sporing (conidiating) tip can be very
similar to the normal hyphal tip, or it can be differentiated. The
most common differentiation is the formation of a bottle shaped cell
called a phialide, from which the spores are produced. As all of these
asexual structures are not single hyphae. In some groups, the
conidiophores (the structures that bear the conidia) are aggregated to
form a thick structure.
E.g. In the order Moniliales, all of them are single hyphae with the
exception of the aggregations, termed as coremia or synnema. These
produce structures rather like corn-stokes, with many conidia being
produced in a mass from the aggregated conidiophores.
The diverse conidia and conidiophores sometimes develop in asexual
sporocarps with different characteristics (e.g. aecervulus, pycnidium,
sporodochium). Some species of Ascomycetes form their structures
within plant tissue, either as parasite or saprophytes. These fungi
have evolved more complex asexual sporing structures, probably
influenced by the cultural conditions of plant tissue as a substrate.
These structures are called the sporodochium. This is a cushion of
conidiophores created from a pseudoparenchymatous stroma in plant
tissue. The pycnidium is a globose to flask-shaped parenchymatous
structure, lined on its inner wall with conidiophores. The acervulus
is a flat saucer shaped bed of conidiophores produced under a plant
cuticle, which eventually erupt through the cuticle for dispersal.
Asexual reproduction process in ascomycetes also involves the budding
which we clearly observe in yeast. This is termed a “blastic
process”. It involves the blowing out or blebbing of the hyphal tip
wall. The blastic process can involve all wall layers, or there can be
a new cell wall synthesized which is extruded from within the old
The initial events of budding can be seen as the development of a ring
of chitin around the point where the bud is about to appear. This
reinforces and stabilizes the cell wall. Enzymatic activity and turgor
pressure act to weaken and extrude the cell wall. New cell wall
material is incorporated during this phase. Cell contents are forced
into the progeny cell, and as the final phase of mitosis ends a cell
plate, the point at which a new cell wall will grow inwards from,
Characteristics of ascomycetes:
Ascomycota are morphologically diverse. The group includes
organisms from unicellular yeasts to complex cup fungi.
· There are 2000 identified genera and 30,000 species of Ascomycota.
· The unifying characteristic among these diverse groups is the
presence of a reproductive structure known as the ascus, though in
some cases it has a reduced role in the life cycle.
· Many ascomycetes are of commercial importance. Some play a
beneficial role, such as the yeasts used in baking, brewing, and wine
fermentation, plus truffles and morels, which are held as gourmet
· Many of them cause tree diseases, such as
Dutch elm disease
Dutch elm disease and
· Some of the plant pathogenic ascomycetes are apple scab, rice
blast, the ergot fungi, black knot, and the powdery mildews.
· The yeasts are used to produce alcoholic beverages and breads. The
Penicillium is used to produce the anti-biotic penicillin.
· Almost half of all members of the phylum
Ascomycota form symbiotic
associations with algae to form lichens.
· Others, such as morels (a highly prized edible fungi), form
important mychorrhizal relationships with plants, thereby providing
enhanced water and nutrient uptake and, in some cases, protection from
· Almost all ascomycetes are terrestrial or parasitic. However, a few
have adapted to marine or freshwater environments.
· The cell walls of the hyphae are variably composed of chitin and
β-glucans, just as in Basidiomycota. However, these fibers are set in
a matrix of glycoprotein containing the sugars galactose and mannose.
· The mycelium of ascomycetes is usually made up of septate hyphae.
However, there is not necessarily any fixed number of nuclei in each
of the divisions.
· The septal walls have septal pores which provide cytoplasmic
continuity throughout the individual hyphae. Under appropriate
conditions, nuclei may also migrate between septal compartments
through the septal pores.
· A unique character of the
Ascomycota (but not present in all
ascomycetes) is the presence of Woronin bodies on each side of the
septa separating the hyphal segments which control the septal pores.
If an adjoining hypha is ruptured, the Woronin bodies block the pores
to prevent loss of cytoplasm into the ruptured compartment. The
Woronin bodies are spherical, hexagonal, or rectangular membrane bound
structures with a crystalline protein matrix.
Modern classification of Ascomycota
There are three subphyla that are described and accepted:
Pezizomycotina are the largest subphylum and contains all
ascomycetes that produce ascocarps (fruiting bodies), except for one
genus, Neolecta, in the Taphrinomycotina. It is roughly equivalent to
the previous taxon, Euascomycetes. The
Pezizomycotina includes most
macroscopic "ascos" such as truffles, ergot, ascolichens, cup fungi
(discomycetes), pyrenomycetes, lorchels, and caterpillar fungus. It
also contains microscopic fungi such as powdery mildews, dermatophytic
fungi, and Laboulbeniales.
Saccharomycotina comprise most of the "true" yeasts, such as
baker's yeast and Candida, which are single-celled (unicellular)
fungi, which reproduce vegetatively by budding. Most of these species
were previously classified in a taxon called Hemiascomycetes.
Taphrinomycotina include a disparate and basal group within the
Ascomycota that was recognized following molecular (DNA) analyses. The
taxon was originally named
Archiascomycetes (or Archaeascomycetes). It
includes both hyphal fungi (Neolecta, Taphrina, Archaeorhizomyces),
fission yeasts (Schizosaccharomyces), and the mammalian lung parasite,
Outdated taxon names
Several outdated taxon names—based on morphological features—are
still occasionally used for species of the Ascomycota. These include
the following sexual (teleomorphic) groups, defined by the structures
of their sexual fruiting bodies: the Discomycetes, which included all
species forming apothecia; the Pyrenomycetes, which included all sac
fungi that formed perithecia or pseudothecia, or any structure
resembling these morphological structures; and the Plectomycetes,
which included those species that form cleistothecia. Hemiascomycetes
included the yeasts and yeast-like fungi that have now been placed
Saccharomycotina or Taphrinomycotina, while the Euascomycetes
included the remaining species of the Ascomycota, which are now in the
Pezizomycotina, and the Neolecta, which are in the Taphrinomycotina.
Some ascomycetes do not reproduce sexually or are not known to produce
asci and are therefore anamorphic species. Those anamorphs that
produce conidia (mitospores) were previously described as Mitosporic
Ascomycota. Some taxonomists placed this group into a separate
artificial phylum, the
Deuteromycota (or "
Fungi Imperfecti"). Where
recent molecular analyses have identified close relationships with
ascus-bearing taxa, anamorphic species have been grouped into the
Ascomycota, despite the absence of the defining ascus. Sexual and
asexual isolates of the same species commonly carry different binomial
species names, as, for example,
Aspergillus nidulans and Emericella
nidulans, for asexual and sexual isolates, respectively, of the same
Species of the
Deuteromycota were classified as Coelomycetes if they
produced their conidia in minute flask- or saucer-shaped conidiomata,
known technically as pycnidia and acervuli. The
those species where the conidiophores (i.e., the hyphal structures
that carry conidia-forming cells at the end) are free or loosely
organized. They are mostly isolated but sometimes also appear as
bundles of cells aligned in parallel (described as synnematal) or as
cushion-shaped masses (described as sporodochial).
A member of the
Cordyceps genus which is parasitic on arthropods. Note
the elongated stromata.
Species unknown, perhaps
Most species grow as filamentous, microscopic structures called hyphae
or as budding single cells (yeasts). Many interconnected hyphae form a
thallus usually referred to as the mycelium, which—when visible to
the naked eye (macroscopic)—is commonly called mold. During sexual
Ascomycota typically produce large numbers of asci.
The ascus is often contained in a multicellular, occasionally readily
visible fruiting structure, the ascocarp (also called an ascoma).
Ascocarps come in a very large variety of shapes: cup-shaped,
club-shaped, potato-like, spongy, seed-like, oozing and pimple-like,
coral-like, nit-like, golf-ball-shaped, perforated tennis ball-like,
cushion-shaped, plated and feathered in miniature (Laboulbeniales),
microscopic classic Greek shield-shaped, stalked or sessile. They can
appear solitary or clustered. Their texture can likewise be very
variable, including fleshy, like charcoal (carbonaceous), leathery,
rubbery, gelatinous, slimy, powdery, or cob-web-like. Ascocarps come
in multiple colors such as red, orange, yellow, brown, black, or, more
rarely, green or blue. Some ascomyceous fungi, such as Saccharomyces
cerevisiae, grow as single-celled yeasts, which—during sexual
reproduction—develop into an ascus, and do not form fruiting bodies.
The "candlesnuff fungus" in its asexual state,
In lichenized species, the thallus of the fungus defines the shape of
the symbiotic colony. Some dimorphic species, such as Candida
albicans, can switch between growth as single cells and as
filamentous, multicellular hyphae. Other species are pleomorphic,
exhibiting asexual (anamorphic) as well as a sexual (teleomorphic)
Except for lichens, the non-reproductive (vegetative) mycelium of most
ascomycetes is usually inconspicuous because it is commonly embedded
in the substrate, such as soil, or grows on or inside a living host,
and only the ascoma may be seen when fruiting. Pigmentation, such as
melanin in hyphal walls, along with prolific growth on surfaces can
result in visible mold colonies; examples include Cladosporium
species, which form black spots on bathroom caulking and other moist
areas. Many ascomycetes cause food spoilage, and, therefore, the
pellicles or moldy layers that develop on jams, juices, and other
foods are the mycelia of these species or occasionally Mucoromycotina
and almost never Basidiomycota. Sooty molds that develop on plants,
especially in the tropics are the thalli of many
The ascocarp of a morel contains numerous apothecia.
Large masses of yeast cells, asci or ascus-like cells, or conidia can
also form macroscopic structures. For example.
can colonize lung cavities (visible in x-rays), causing a form of
pneumonia. Asci of
Ascosphaera fill honey bee larvae and pupae
causing mummification with a chalk-like appearance, hence the name
"chalkbrood". Yeasts for small colonies in vitro and in vivo, and
excessive growth of Candida species in the mouth or vagina causes
"thrush", a form of candidiasis.
The cell walls of the ascomycetes almost always contain chitin and
β-glucans, and divisions within the hyphae, called "septa", are the
internal boundaries of individual cells (or compartments). The cell
wall and septa give stability and rigidity to the hyphae and may
prevent loss of cytoplasm in case of local damage to cell wall and
cell membrane. The septa commonly have a small opening in the center,
which functions as a cytoplasmic connection between adjacent cells,
also sometimes allowing cell-to-cell movement of nuclei within a
hypha. Vegetative hyphae of most ascomycetes contain only one nucleus
per cell (uninucleate hyphae), but multinucleate cells—especially in
the apical regions of growing hyphae—can also be present.
In common with other fungal phyla, the
Ascomycota are heterotrophic
organisms that require organic compounds as energy sources. These are
obtained by feeding on a variety of organic substrates including dead
matter, foodstuffs, or as symbionts in or on other living organisms.
To obtain these nutrients from their surroundings, ascomycetous fungi
secrete powerful digestive enzymes that break down organic substances
into smaller molecules, which are then taken up into the cell. Many
species live on dead plant material such as leaves, twigs, or logs.
Several species colonize plants, animals, or other fungi as parasites
or mutualistic symbionts and derive all their metabolic energy in form
of nutrients from the tissues of their hosts.
Owing to their long evolutionary history, the
Ascomycota have evolved
the capacity to break down almost every organic substance. Unlike most
organisms, they are able to use their own enzymes to digest plant
biopolymers such as cellulose or lignin. Collagen, an abundant
structural protein in animals, and keratin—a protein that forms hair
and nails—, can also serve as food sources. Unusual examples include
Aureobasidium pullulans, which feeds on wall paint, and the kerosene
fungus Amorphotheca resinae, which feeds on aircraft fuel (causing
occasional problems for the airline industry), and may sometimes block
fuel pipes. Other species can resist high osmotic stress and grow,
for example, on salted fish, and a few ascomycetes are aquatic.
Ascomycota is characterized by a high degree of specialization;
for instance, certain species of
Laboulbeniales attack only one
particular leg of one particular insect species. Many Ascomycota
engage in symbiotic relationships such as in lichens—symbiotic
associations with green algae or cyanobacteria—in which the fungal
symbiont directly obtains products of photosynthesis. In common with
many basidiomycetes and Glomeromycota, some ascomycetes form symbioses
with plants by colonizing the roots to form mycorrhizal associations.
Ascomycota also represents several carnivorous fungi, which have
developed hyphal traps to capture small protists such as amoebae, as
well as roundworms (Nematoda), rotifers, tardigrades, and small
arthropods such as springtails (Collembola).
Hypomyces completus on culture medium
Distribution and living environment
Ascomycota are represented in all land ecosystems worldwide,
occurring on all continents including Antarctica. Spores and
hyphal fragments are dispersed through the atmosphere and freshwater
environments, as well as ocean beaches and tidal zones. The
distribution of species is variable; while some are found on all
continents, others, as for example the white truffle Tuber magnatum,
only occur in isolated locations in Italy and Eastern Europe. The
distribution of plant-parasitic species is often restricted by host
distributions; for example,
Cyttaria is only found on Nothofagus
(Southern Beech) in the Southern Hemisphere.
Asexual reproduction is the dominant form of propagation in the
Ascomycota, and is responsible for the rapid spread of these fungi
into new areas. It occurs through vegetative reproductive spores, the
conidia. The conidiospores commonly contain one nucleus and are
products of mitotic cell divisions and thus are sometimes called
mitospores, which are genetically identical to the mycelium from which
they originate. They are typically formed at the ends of specialized
hyphae, the conidiophores. Depending on the species they may be
dispersed by wind or water, or by animals.
Different types of asexual spores can be identified by colour, shape,
and how they are released as individual spores.
Spore types can be
used as taxonomic characters in the classification within the
Ascomycota. The most frequent types are the single-celled spores,
which are designated amerospores. If the spore is divided into two by
a cross-wall (septum), it is called a didymospore.
Conidiospores of Trichoderma aggressivum, Diameter approx. 3µm
Conidiophores of molds of the genus Aspergillus, conidiogenesis is
Conidiophores of Trichoderma harzianum, conidiogenesis is
Conidiophores of Trichoderma fertile with vase-shaped phialides and
newly formed conidia on their ends (bright points)
When there are two or more cross-walls, the classification depends on
spore shape. If the septae are transversal, like the rungs of a
ladder, it is a phragmospore, and if they possess a net-like structure
it is a dictyospore. In staurospores ray-like arms radiate from a
central body; in others (helicospores) the entire spore is wound up in
a spiral like a spring. Very long worm-like spores with a
length-to-diameter ratio of more than 15:1, are called scolecospores.
Conidiogenesis and dehiscence
Important characteristics of the anamorphs of the
conidiogenesis, which includes spore formation and dehiscence
(separation from the parent structure). Conidiogenesis corresponds to
Embryology in animals and plants and can be divided into two
fundamental forms of development: blastic conidiogenesis, where the
spore is already evident before it separates from the conidiogenic
hypha, and thallic conidiogenesis, during which a cross-wall forms and
the newly created cell develops into a spore. The spores may or may
not be generated in a large-scale specialized structure that helps to
These two basic types can be further classified as follows:
blastic-acropetal (repeated budding at the tip of the conidiogenic
hypha, so that a chain of spores is formed with the youngest spores at
blastic-synchronous (simultaneous spore formation from a central cell,
sometimes with secondary acropetal chains forming from the initial
blastic-sympodial (repeated sideways spore formation from behind the
leading spore, so that the oldest spore is at the main tip),
blastic-annellidic (each spore separates and leaves a ring-shaped scar
inside the scar left by the previous spore),
blastic-phialidic (the spores arise and are ejected from the open ends
of special conidiogenic cells called phialides, which remain constant
basauxic (where a chain of conidia, in successively younger stages of
development, is emitted from the mother cell),
blastic-retrogressive (spores separate by formation of crosswalls near
the tip of the conidiogenic hypha, which thus becomes progressively
thallic-arthric (double cell walls split the conidiogenic hypha into
cells that develop into short, cylindrical spores called
arthroconidia; sometimes every second cell dies off, leaving the
thallic-solitary (a large bulging cell separates from the conidiogenic
hypha, forms internal walls, and develops to a phragmospore).
Sometimes the conidia are produced in structures visible to the naked
eye, which help to distribute the spores. These structures are called
"conidiomata" (singular: conidioma), and may take the form of pycnidia
(which are flask-shaped and arise in the fungal tissue) or acervuli
(which are cushion-shaped and arise in host tissue).
Dehiscence happens in two ways. In schizolytic dehiscence, a
double-dividing wall with a central lamella (layer) forms between the
cells; the central layer then breaks down thereby releasing the
spores. In rhexolytic dehiscence, the cell wall that joins the spores
on the outside degenerates and releases the conidia.
Heterokaryosis and parasexuality
Ascomycota species are not known to have a sexual cycle. Such
asexual species may be able to undergo genetic recombination between
individuals by processes involving heterokaryosis and parasexual
Parasexuality refers to the process of heterokaryosis, caused by
merging of two hyphae belonging to different individuals, by a process
called anastomosis, followed by a series of events resulting in
genetically different cell nuclei in the mycelium. The merging of
nuclei is not followed by meiotic events, such as gamete formation and
results in an increased number of chromosomes per nuclei. Mitotic
crossover may enable recombination, i.e., an exchange of genetic
material between homologous chromosomes. The chromosome number may
then be restored to its haploid state by nuclear division, with each
daughter nuclei being genetically different from the original parent
nuclei. Alternatively, nuclei may lose some chromosomes, resulting
in aneuploid cells.
Candida albicans (class Saccharomycetes) is an
example of a fungus that has a parasexual cycle (see Candida albicans
and Parasexual cycle).
Ascus of Hypocrea virens with eight two-celled Ascospores
Sexual reproduction in the
Ascomycota leads to the formation of the
ascus, the structure that defines this fungal group and distinguishes
it from other fungal phyla. The ascus is a tube-shaped vessel, a
meiosporangium, which contains the sexual spores produced by meiosis
and which are called ascospores.
Apart from a few exceptions, such as Candida albicans, most
ascomycetes are haploid, i.e., they contain one set of chromosomes per
nucleus. During sexual reproduction there is a diploid phase, which
commonly is very short, and meiosis restores the haploid state. The
sexual cycle of one well-studied representative species of Ascomycota
is described in greater detail in Neurospora crassa.
Formation of sexual spores
The sexual part of the life cycle commences when two hyphal structures
mate. In the case of homothallic species, mating is enabled between
hyphae of the same fungal clone, whereas in heterothallic species, the
two hyphae must originate from fungal clones that differ genetically,
i.e., those that are of a different mating type.
Mating types are
typical of the fungi and correspond roughly to the sexes in plants and
animals; however one species may have more than two mating types,
resulting in sometimes complex vegetative incompatibility systems. The
adaptive function of mating type is discussed in Neurospora crassa.
Gametangia are sexual structures formed from hyphae, and are the
generative cells. A very fine hypha, called trichogyne emerges from
one gametangium, the ascogonium, and merges with a gametangium (the
antheridium) of the other fungal isolate. The nuclei in the
antheridium then migrate into the ascogonium, and plasmogamy—the
mixing of the cytoplasm—occurs. Unlike in animals and plants,
plasmogamy is not immediately followed by the merging of the nuclei
(called karyogamy). Instead, the nuclei from the two hyphae form
pairs, initiating the dikaryophase of the sexual cycle, during which
time the pairs of nuclei synchronously divide. Fusion of the paired
nuclei leads to mixing of the genetic material and recombination and
is followed by meiosis. A similar sexual cycle is present in the blue
green algae (Rhodophyta). A discarded hypothesis held that a second
karyogamy event occurred in the ascogonium prior to ascogeny,
resulting in a tetraploid nucleus which divided into four diploid
nuclei by meiosis and then into eight haploid nuclei by a supposed
process called brachymeiosis, but this hypothesis was disproven in the
Unitunicate-inoperculate Asci of Hypomyces chrysospermus
From the fertilized ascogonium, dinucleate hyphae emerge in which each
cell contains two nuclei. These hyphae are called ascogenous or
fertile hyphae. They are supported by the vegetative mycelium
containing uni– (or mono–) nucleate hyphae, which are sterile. The
mycelium containing both sterile and fertile hyphae may grow into
fruiting body, the ascocarp, which may contain millions of fertile
The sexual structures are formed in the fruiting layer of the
ascocarp, the hymenium. At one end of ascogenous hyphae,
characteristic U-shaped hooks develop, which curve back opposite to
the growth direction of the hyphae. The two nuclei contained in the
apical part of each hypha divide in such a way that the threads of
their mitotic spindles run parallel, creating two pairs of genetically
different nuclei. One daughter nucleus migrates close to the hook,
while the other daughter nucleus locates to the basal part of the
hypha. The formation of two parallel cross-walls then divides the
hypha into three sections: one at the hook with one nucleus, one at
the basal of the original hypha that contains one nucleus, and one
that separates the U-shaped part, which contains the other two nuclei.
Diagram of an apothecium (the typical cup-like reproductive structure
of Ascomycetes) showing sterile tissues as well as developing and
Fusion of the nuclei (karyogamy) takes place in the U-shaped cells in
the hymenium, and results in the formation of a diploid zygote. The
zygote grows into the ascus, an elongated tube-shaped or
Meiosis then gives rise to four haploid
nuclei, usually followed by a further mitotic division that results in
eight nuclei in each ascus. The nuclei along with some cytoplasma
become enclosed within membranes and a cell wall to give rise to
ascospores that are aligned inside the ascus like peas in a pod. (For
a general description of meiosis and its adaptive function see Meiosis
and Bernstein and Bernstein).
Upon opening of the ascus, ascospores may be dispersed by the wind,
while in some cases the spores are forcibly ejected form the ascus;
certain species have evolved spore cannons, which can eject ascospores
up to 30 cm. away. When the spores reach a suitable substrate,
they germinate, form new hyphae, which restarts the fungal life cycle.
The form of the ascus is important for classification and is divided
into four basic types: unitunicate-operculate,
unitunicate-inoperculate, bitunicate, or prototunicate. See the
article on asci for further details.
Ascomycota fulfil a central role in most land-based ecosystems.
They are important decomposers, breaking down organic materials, such
as dead leaves and animals, and helping the detritivores (animals that
feed on decomposing material) to obtain their nutrients. Ascomycetes
along with other fungi can break down large molecules such as
cellulose or lignin, and thus have important roles in nutrient cycling
such as the carbon cycle.
The fruiting bodies of the
Ascomycota provide food for many animals
ranging from insects and slugs and snails (Gastropoda) to rodents and
larger mammals such as deer and wild boars.
Many ascomycetes also form symbiotic relationships with other
organisms, including plants and animals.
Main article: Lichen
Probably since early in their evolutionary history, the Ascomycota
have formed symbiotic associations with green algae (Chlorophyta), and
other types of algae and cyanobacteria. These mutualistic associations
are commonly known as lichens, and can grow and persist in terrestrial
regions of the earth that are inhospitable to other organisms and
characterized by extremes in temperature and humidity, including the
Arctic, the Antarctic, deserts, and mountaintops. While the
photoautotrophic algal partner generates metabolic energy through
photosynthesis, the fungus offers a stable, supportive matrix and
protects cells from radiation and dehydration. Around 42% of the
Ascomycota (about 18,000 species) form lichens, and almost all the
fungal partners of lichens belong to the Ascomycota.
Mycorrhizal fungi and endophytes
Members of the
Ascomycota form two important types of relationship
with plants: as mycorrhizal fungi and as endophytes.
symbiotic associations of fungi with the root systems of the plants,
which can be of vital importance for growth and persistence for the
plant. The fine mycelial network of the fungus enables the increased
uptake of mineral salts that occur at low levels in the soil. In
return, the plant provides the fungus with metabolic energy in the
form of photosynthetic products.
Endophytic fungi live inside plants, and those that form mutualistic
or commensal associations with their host, do not damage their hosts.
The exact nature of the relationship between endophytic fungus and
host depends on the species involved, and in some cases fungal
colonization of plants can bestow a higher resistance against insects,
roundworms (nematodes), and bacteria; in the case of grass endophytes
the fungal symbiont produces poisonous alkaloids, which can affect the
health of plant-eating (herbivorous) mammals and deter or kill insect
Symbiotic relationships with animals
Several ascomycetes of the genus
Xylaria colonize the nests of
leafcutter ants and other fungus-growing ants of the tribe Attini, and
the fungal gardens of termites (Isoptera). Since they do not generate
fruiting bodies until the insects have left the nests, it is suspected
that, as confirmed in several cases of
Basidiomycota species, they may
be cultivated.[clarification needed]
Bark beetles (family Scolytidae) are important symbiotic partners of
ascomycetes. The female beetles transport fungal spores to new hosts
in characteristic tucks in their skin, the mycetangia. The beetle
tunnels into the wood and into large chambers in which they lay their
eggs. Spores released from the mycetangia germinate into hyphae, which
can break down the wood. The beetle larvae then feed on the fungal
mycelium, and, on reaching maturity, carry new spores with them to
renew the cycle of infection. A well-known example of this is Dutch
elm disease, caused by Ophiostoma ulmi, which is carried by the
European elm bark beetle, Scolytus multistriatus.
Importance for humans
Tree attacked by the Bluestain fungus, Ophiostoma minus
Ascomycetes make many contributions to the good of humanity, and also
have many ill effects.
One of their most harmful roles is as the agent of many plant
diseases. For instance:
Dutch Elm Disease, caused by the closely related species Ophiostoma
ulmi and Ophiostoma novo-ulmi, has led to the death of many elms in
Europe and North America.
Claviceps purpurea on rye (Secale cereale)
The originally Asian Cryphonectria parasitica is responsible for
attacking Sweet Chestnuts (Castanea sativa), and virtually eliminated
American Chestnut (Castanea dentata),
A disease of maize (Zea mays), which is especially prevalent in North
America, is brought about by Cochliobolus heterostrophus.
Taphrina deformans causes leaf curl of peach.
Uncinula necator is responsible for the disease powdery mildew, which
Monilinia cause brown rot of stone fruit such as peaches
(Prunus persica) and sour cherries (Prunus ceranus).
Members of the
Ascomycota such as
Stachybotrys chartarum are
responsible for fading of woollen textiles, which is a common problem
especially in the tropics.
Blue-green, red and brown molds attack and spoil foodstuffs - for
Penicillium italicum rots oranges.
Cereals infected with
Fusarium graminearum contain mycotoxins like
deoxynivalenol (DON), which can lead to skin and mucous membrane
lesions when eaten by pigs.
Ergot (Claviceps purpurea) is a direct menace to humans when it
attacks wheat or rye and produces highly poisonous and carcinogenic
alkaloids, causing ergotism if consumed. Symptoms include
hallucinations, stomach cramp, and a burning sensation in the limbs
("Saint Anthony's Fire").
Aspergillus flavus, which grows on peanuts and other hosts, generates
aflatoxin, which damages the liver and is highly carcinogenic.
Candida albicans, a yeast that attacks the mucous membranes, can cause
an infection of the mouth or vagina called thrush or candidiasis, and
is also blamed for "yeast allergies".
Epidermophyton cause skin infections but are not very
dangerous for people with healthy immune systems. However, if the
immune system is damaged they can be life-threatening; for instance,
Pneumocystis jirovecii is responsible for severe lung infections that
On the other hand, ascus fungi have brought some important benefits to
The most famous case may be that of the mould
Penicillium notatum), which, probably to attack competing
bacteria, produces an antibiotic that, under the name of penicillin,
triggered a revolution in the treatment of bacterial infectious
diseases in the 20th century.
The medical importance of
Tolypocladium niveum as an immunosuppressor
can hardly be exaggerated. It excretes Ciclosporin, which, as well as
being given during
Organ transplantation to prevent rejection, is also
prescribed for auto-immune diseases such as multiple sclerosis,
although there is some doubt over the long-term side-effects of the
Stilton cheese veined with
Some ascomycete fungi can be altered relatively easily through genetic
engineering procedures. They can then produce useful proteins such as
insulin, human growth hormone, or TPa, which is employed to dissolve
Several species are common model organisms in biology, including
Schizosaccharomyces pombe, and Neurospora
crassa. The genomes of a number of ascomycete fungi have been fully
Yeast (Saccharomyces cerevisiae) is used to make bread, beer
and wine, during which process sugars such as glucose or sucrose are
fermented to make ethanol and carbon dioxide. Bakers use the yeast for
carbon dioxide production, causing the bread to rise, with the ethanol
boiling off during cooking. Most vintners use it for ethanol
production, with the carbon dioxide being released into the atmosphere
during fermentation. Brewers and traditional producers of sparkling
wine use both, with a primary fermentation for the alcohol and a
secondary one to produce the carbon dioxide bubbles that provide the
drinks with "sparkling" texture in the case of wine and the desirable
foam in the case of beer.
Penicillium camemberti play a role in the manufacture of
Camembert and Brie, while those of
do the same for Gorgonzola,
Roquefort and Stilton.
Aspergillus oryzae is added to a pulp of soaked soya beans to
make soy sauce, and is used to break down starch in rice and other
grains into simple sugars for fermentation into East Asian alcoholic
beverages such as huangjiu and sake.
Finally, some members of the
Ascomycota are choice edibles; morels
Morchella spp.), truffles (Tuber spp.), and lobster mushroom
(Hypomyces lactifluorum) are some of the most sought-after fungal
Ascomycota families incertae sedis
Ascomycota genera incertae sedis
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Wikispecies has information related to Ascomycota
Alexopoulos, C.J.; Mims, C.W.; Blackwell, M. (1996). Introductory
Mycology. Wiley. ISBN 0-471-52229-5.
Deacon, J. (2005). Fungal Biology. Blackwell.
Jennings DH, Lysek G (1996). Fungal Biology: Understanding the Fungal
Lifestyle. Guildford, UK: Bios Scientific.
Kirk PM, Cannon PF, Minter DW, Stalpers JA (2008). Dictionary of the
Fungi (10th ed.). Wallingford: CABI. ISBN 0-85199-826-7.
Taylor EL, Taylor TN (1993). The Biology and Evolution of Fossil
Plants. Prentice Hall. ISBN 0-13-651589-4.
Metamonada (Anaeromonada, Trichozoa)
Conosa (Archamoebae, Semiconosia)
Lobosa (Cutosea, Discosea, Tubulinea)
Metazoa or Animals
Major kingdoms are underlined. See also: protist. Sources and
alternative views: Wikispecies.
Opisthokont: True fungi classification, fungal orders
Fungal phyla are underlined. See also: fungi imperfecti (polyphyletic