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Go strategy and tactics

The game of Go has simple rules that can be learned very quickly but, as with chess and similar board games, complex strategies may be employed by experienced players.

Go opening theory
The whole board opening is called fuseki. An important principle to follow in early play is "corner, side, center." In other words, the corners are the easiest places to take territory, because two sides of the board can be used as boundaries. Once the corners are occupied, the next most valuable points are along the sides, aiming to use the edge as a territorial boundary. Capturing territory in the middle, where it must be surrounded on all four sides, is extremely difficult. The same is true for founding a living group: Easiest in the corner, most difficult in the center.

The first moves are usually played on or near the 4-4 star points in the corners, because in those places it is easiest to gain territory or influence. In order to be totally secure alone, a corner stone must be placed on the 3-3 point. However, if a stone is placed at a 4-4 point and the opponent invades, the first player can build a surrounding wall as the second (invader) is forming a live group, thus exerting strong influence on a large area.

After that, standard sequences (Joseki) can be used to develop corner positions, and extensions along the side can be made. Usually, the center area is kept empty the longest. Plays are usually on the third or fourth line—the second makes too little territory, while the fifth is too easily undermined by a play on the third. A play on the fourth line is directed more towards influence to the center, a play on the third line more towards making territory along the side.

Connection and separation
A fundamental Go strategy involves keeping stones connected. Connecting a group with one eye to another one-eyed group makes them live together. Connecting individual stones into a single group results in an increase of liberties; for instance, a single stone played in the center of the board has four liberties, while two adjacent stones in the center of the board form a unit with six; to capture the unit, an opponent would have to play stones on all of its liberties. Thus connected stones are stronger because they share their liberties. While two separate stones have a total of up to eight liberties, they can be captured separately from one another.

Since connecting stones keeps them secure, an important offensive tactic is to prevent the opponent from connecting their stones, while at the same time keeping one's own stones connected. This act of dividing the opponent's stones into separate groups is called cutting.

While one should generally try to keep one's own stones connected, situations exist where doing so would be a wasted move. Stones are considered tactically connected if no move by the opposing player could prevent them from being connected.

In a handicap game, Black starts with two or more handicap stones played before White's first move. If played in the traditional places on the "star points", these stones will be useful for the purpose of connection and separation of stones played closer to the edge ("lower"), as well as in many other ways. Right from the start, the White player's stones are under threat of separation, whereas Black starts with numerous potential connections.

An example of inefficiency or poor coordination of stones in the context of connection is the empty triangle, where the stones are arranged so that they share fewer liberties than if they were deployed in a straight line.

Life and death
A key concept in the tactics of Go, though not part of the rules, is the classification of groups of stones into alive, dead or unsettled.

At the end of the game, groups that cannot avoid being captured during normal play are removed as captures. These stones are dead. Groups can reach this state much earlier during play; a group of stones can quickly run out of options so that further play to save them is fruitless, or even detrimental. Similarly, further play to capture such a group is often of no benefit, except when securing liberties for an adjacent group, since if it remains on the board at the end of the game it is captured anyway. Thus groups can be considered "dead as they stand", or just dead, by both sides during the course of the game.

Groups enclosing an area completely can be harder to kill. Normally, when a play causes an area completely enclosed by the opponent to become filled, the group filling the area is captured since it has no remaining liberties (such a play is called "suicide"). Only if the last play inside the area would kill the enclosing group, thus freeing one or more liberties for the group that filled the space, can the play be considered. This can only be achieved if the liberties on the outside of the enclosing group have been covered first. Thus, enclosing an area of one or more liberties (called an eye) can make the group harder to kill, since the opponent must cover all of its external liberties before covering the final, internal liberty.

From this, it is possible to create groups that cannot be killed at all. If a group encloses two or more separate areas (two or more eyes), the opponent cannot simultaneously fill both of them with a single play, and thus can never play on the last liberty of the group. Such a group, or a group that cannot be prevented from forming such an enclosure, is called alive.

Groups which are not definitely alive nor definitely dead are sometimes called unsettled groups. Much of the tactical fighting in Go focuses on making one's own groups live, by ensuring they can make two eyes, and on making the opponent's groups die, by denying them two eyes.

Reading
Determining ahead of time whether a group is currently alive, dead, or unsettled, requires the ability to extrapolate from the current position and imagine possible plays by both sides, the best responses to those plays, the best responses to those responses, and so on. This is called reading ahead, or just reading, and it is a skill that grows with experience. Many players study books of life and death problems to increase their skill at reading more and more complicated positions.

One of the most important skills required for strong tactical play is the ability to read ahead. Reading ahead consists of considering available moves to play, considering the possible responses to each move, the subsequent possibilities after each of those responses, etcetera. Some of the strongest players of the game can read up to 40 moves ahead even in complicated positions.

In general, go players refer to analysis of positions as reading. One major purpose of reading is to be sure that a local position can be neglected for a while. For instance, a player may be able to make gains by playing for a certain patch of territory. Yet, this play may be worth only a few points, and thus deemed unnecessary, depending on the state of the game. With confidence in one's reading, it becomes much easier to set priorities and switch around the board (see sente). Not changing gears at the correct time can be a loss of opportunity.

High and low
In order to build a harmonious position, usually in the opening, one does not place all stones on the third line (for territory), nor all stones on the fourth line (for center influence). "Harmonious" as used here is not just an aesthetic quality; rather, it stands for a balance in the overall (strategic) connection of the stones.

Thickness and lightness
An outward-facing position that cannot be attacked, that is, one which can easily get two eyes or connect to a friendly live group and so does not need to answer enemy moves close by, is called thick. Thick positions are important as they radiate influence across the board. An error that is often made by weaker players is to make territory in front of their thick position; this is inefficient because the player is likely to get that territory anyway. Doing so is also inflexible strategically, so invites enemy forcing moves at the border of the incomplete territory. Thickness is better used from a distance, as support for other actions.

For example, if Black has a thick group and a weak group nearby, and White attacks the weak group, Black can have its weak group run towards its thick group. If successful, the strength of the thick group will protect the weak group. Or, if White tries to invade near a thick group, Black can try to push White towards its thick group. If Black is successful, the strength of the thick group may help destroy the invasion. Even if the invaders are not killed, the pressure exerted by the thick position can allow Black to profit from the attack, for example gaining territory or thickness in a neighbouring area whilst chasing the weak stones. A thick group can also support invasion of enemy spheres of influence.

A light group is also one that is hard to attack, but for a different reason. If a group has a large number of options, often including the sacrifice of part of it, it is called light. Because it is usually impossible to take away all or almost all options, attacking such a group is very hard for the opponent and brings little advantage. A weak group which is too important to sacrifice is called heavy.

Attack and defense
A large part of the middle game of a game of Go may be spent by one player attacking the other player's weak group(s). What is important to remember is that in most cases the goal of an attack is not to kill the attacked group, but to gain territory or influence. The attack is more or less used to restrict the opponent's options and make it impossible for them to make territory or influence.

Ko fighting
Suppose that Black begins a ko by taking a stone of White's. White cannot immediately recapture; the rules state that white must, for the moment, play elsewhere. White may believe that good strategy requires they eventually recapture, but Black, on their next turn, will have the option of ending the ko, for example by filling in the spot White would use to recapture. To prevent Black from doing this, White can play a ko threat.

A ko threat is a move that forces one's opponent to respond, or risk a punishing blow. A ko threat by White will force Black to choose between responding to the threat, and allowing White to recapture (thereby continuing the ko), or ending the ko, but having a damaged, poor position elsewhere on the board.

A good ko threat should threaten more damage to one's opponent's position than the value of losing the ko. If the ko is then lost, the trade was still beneficial.

Sente and gote
The concepts of sente and gote are important in higher level Go strategy.

A player whose moves compel the opponent to respond in a local position is said to have sente (先手), meaning the player has the initiative; the opponent is said to have gote (後手). Sente means 'preceding move' (lit: 'before hand'), whereas gote means 'succeeding move' (lit: after hand').

One player attacks in sente; the other defends in gote. In most games, the player who is able to maintain sente controls the flow of the game and therefore has a significant advantage. A player usually accepts gote in order to defend a weak position or to achieve a local advantage such as securing territory.

In the endgame (yose) players typically try to play all available sente moves and then play the largest gote move on the board. A reverse sente play is a gote play that prevents the opponent from making a sente move.

When a player ignores an opponent's sente move and plays elsewhere, they are said to play tenuki. Playing tenuki is as a kind of gambit where the player accepts a potential loss on the local level in order seize the initiative by playing elsewhere.

Direction of play
The direction of play is a higher level concept in the opening, relating to the efficiency of stones played on the board. This involves the important trade-off between overconcentration (korigatachi) and vagueness - between playing a move that accomplishes too little and a move that tries to accomplish too much. Additionally, the stones already played are taken into consideration. The players aim not only at making efficient new moves, but also at playing moves that heighten the value of their previous moves, and at achieving maximum harmony in a global sense. One must strive to make each stone played important and valuable, that is, utilize its aji, or potential, to the fullest extent possible. Thus, choosing the correct direction of play requires not only a deep understanding of the value of thickness, but also demands a good sense of positional judgment from the players.

Endgame (yose)
The endgame begins when large-scale contention over life and death, invasion, reduction etc. ends. Players then set about maximizing the boundaries of their territories while minimizing the opponent's territory. One must choose which of these moves is more urgent to play based not only on the points it may gain, but on whether that move is sente. Generally, in the endgame, all the major areas are staked out— however, there are still points to be made, as well as possible ways to reduce the opponent's territory. A simple example would be a move that is dame (neutral point for you), but when filled in, it is sente, requiring white to fill a stone in their territory to answer. It would be thus said this is 'a one-point reduction in sente.'

title: Go strategy and tactics


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Basidiomycota

Basidiomycota is one of two large divisions that, together with the Ascomycota, constitute the subkingdom Dikarya (often referred to as the "higher fungi") within the kingdom Fungi. Members are known as basidiomycetes. More specifically, Basidiomycota includes these groups: agarics, puffballs, stinkhorns, bracket fungi, other polypores, jelly fungi, boletes, chanterelles, earth stars, smuts, bunts, rusts, mirror yeasts, and Cryptococcus, the human pathogenic yeast.

Basidiomycota are filamentous fungi composed of hyphae (except for basidiomycota-yeast) and reproduce sexually via the formation of specialized club-shaped end cells called basidia that normally bear external meiospores (usually four). These specialized spores are called basidiospores. However, some Basidiomycota are obligate asexual reproducers. Basidiomycota that reproduce asexually (discussed below) can typically be recognized as members of this division by gross similarity to others, by the formation of a distinctive anatomical feature (the clamp connection), cell wall components, and definitively by phylogenetic molecular analysis of DNA sequence data.

Classification
A 2007 classification, adopted by a coalition of 67 mycologists recognized three subphyla (Pucciniomycotina, Ustilaginomycotina, Agaricomycotina) and two other class level taxa (Wallemiomycetes, Entorrhizomycetes) outside of these, among the Basidiomycota. As now classified, the subphyla join and also cut across various obsolete taxonomic groups (see below) previously commonly used to describe Basidiomycota. According to a 2008 estimate, Basidiomycota comprise three subphyla (including six unassigned classes) 16 classes, 52 orders, 177 families, 1,589 genera, and 31,515 species. Wijayawardene et al. 2020 produced an update that recognized 19 classes (Agaricomycetes, Agaricostilbomycetes, Atractiellomycetes, Bartheletiomycetes, Classiculomycetes, Cryptomycocolacomycetes, Cystobasidiomycetes, Dacrymycetes, Exobasidiomycetes, Malasseziomycetes, Microbotryomycetes, Mixiomycetes, Monilielliomycetes, Pucciniomycetes, Spiculogloeomycetes, Tremellomycetes, Tritirachiomycetes, Ustilaginomycetes and Wallemiomycetes) with multiple orders and genera.

Traditionally, the Basidiomycota were divided into two classes, now obsolete: Nonetheless these former concepts continue to be used as two types of growth habit groupings, the "mushrooms" (e.g. Schizophyllum commune) and the non-mushrooms (e.g. Ustilago maydis).
 * Homobasidiomycetes (alternatively called holobasidiomycetes), including true mushrooms
 * Heterobasidiomycetes, including the jelly, rust and smut fungi

Agaricomycotina
The Agaricomycotina include what had previously been called the Hymenomycetes (an obsolete morphological based class of Basidiomycota that formed hymenial layers on their fruitbodies), the Gasteromycetes (another obsolete class that included species mostly lacking hymenia and mostly forming spores in enclosed fruitbodies), as well as most of the jelly fungi. This sub-phyla also includes the "classic" mushrooms, polypores, corals, chanterelles, crusts, puffballs and stinkhorns. The three classes in the Agaricomycotina are the Agaricomycetes, the Dacrymycetes, and the Tremellomycetes.

The class Wallemiomycetes is not yet placed in a subdivision, but recent genomic evidence suggests that it is a sister group of Agaricomycotina.

Pucciniomycotina
The Pucciniomycotina include the rust fungi, the insect parasitic/symbiotic genus Septobasidium, a former group of smut fungi (in the Microbotryomycetes, which includes mirror yeasts), and a mixture of odd, infrequently seen, or seldom recognized fungi, often parasitic on plants. The eight classes in the Pucciniomycotina are Agaricostilbomycetes, Atractiellomycetes, Classiculomycetes, Cryptomycocolacomycetes, Cystobasidiomycetes, Microbotryomycetes, Mixiomycetes, and Pucciniomycetes.

Ustilaginomycotina
The Ustilaginomycotina are most (but not all) of the former smut fungi and the Exobasidiales. The classes of the Ustilaginomycotina are the Exobasidiomycetes, the Entorrhizomycetes, and the Ustilaginomycetes.

Genera included
There are several genera classified in the Basidiomycota that are 1) poorly known, 2) have not been subjected to DNA analysis, or 3) if analysed phylogenetically do not group with as yet named or identified families, and have not been assigned to a specific family (i.e., they are incertae sedis with respect to familial placement). These include:

 * Anastomyces W.P.Wu, B.Sutton & Gange (1997)
 * Anguillomyces Marvanová & Bärl. (2000)
 * Anthoseptobasidium Rick (1943)
 * Arcispora Marvanová & Bärl. (1998)
 * Arrasia Bernicchia, Gorjón & Nakasone (2011)
 * Brevicellopsis Hjortstam & Ryvarden (2008)
 * Celatogloea P.Roberts (2005)
 * Cleistocybe Ammirati, A.D.Parker & Matheny (2007)
 * Cystogloea P. Roberts (2006)
 * Dacryomycetopsis Rick (1958)
 * Eriocybe Vellinga (2011)
 * Hallenbergia Dhingra & Priyanka (2011)
 * Hymenoporus Tkalčec, Mešić & Chun Y.Deng (2015)
 * Kryptastrina Oberw. (1990)
 * Microstella K.Ando & Tubaki (1984)
 * Neotyphula Wakef. (1934)
 * Nodulospora Marvanová & Bärl. (2000)
 * Paraphelaria Corner (1966)
 * Punctulariopsis Ghob.-Nejh. (2010)
 * Radulodontia Hjortstam & Ryvarden (2008)
 * Restilago Vánky (2008)
 * Sinofavus W.Y.Zhuang (2008)
 * Zanchia Rick (1958)
 * Zygodesmus Corda (1837)
 * Zygogloea P.Roberts (1994)

Typical life cycle
Unlike animals and plants which have readily recognizable male and female counterparts, Basidiomycota (except for the Rust (Pucciniales)) tend to have mutually indistinguishable, compatible haploids which are usually mycelia being composed of filamentous hyphae. Typically haploid Basidiomycota mycelia fuse via plasmogamy and then the compatible nuclei migrate into each other's mycelia and pair up with the resident nuclei. Karyogamy is delayed, so that the compatible nuclei remain in pairs, called a dikaryon. The hyphae are then said to be dikaryotic. Conversely, the haploid mycelia are called monokaryons. Often, the dikaryotic mycelium is more vigorous than the individual monokaryotic mycelia, and proceeds to take over the substrate in which they are growing. The dikaryons can be long-lived, lasting years, decades, or centuries. The monokaryons are male nor female. They have either a  or a   mating system. This results in the fact that following meiosis, the resulting haploid basidiospores and resultant monokaryons, have nuclei that are compatible with 50% (if bipolar) or 25% (if tetrapolar) of their sister basidiospores (and their resultant monokaryons) because the mating genes must differ for them to be compatible. However, there are sometimes more than two possible alleles for a given locus, and in such species, depending on the specifics, over 90% of monokaryons could be compatible with each other.

The maintenance of the dikaryotic status in dikaryons in many Basidiomycota is facilitated by the formation of clamp connections that physically appear to help coordinate and re-establish pairs of compatible nuclei following synchronous mitotic nuclear divisions. Variations are frequent and multiple. In a typical Basidiomycota lifecycle the long lasting dikaryons periodically (seasonally or occasionally) produce basidia, the specialized usually club-shaped end cells, in which a pair of compatible nuclei fuse (karyogamy) to form a diploid cell. Meiosis follows shortly with the production of 4 haploid nuclei that migrate into 4 external, usually apical basidiospores. Variations occur, however. Typically the basidiospores are ballistic, hence they are sometimes also called ballistospores. In most species, the basidiospores disperse and each can start a new haploid mycelium, continuing the lifecycle. Basidia are microscopic but they are often produced on or in multicelled large fructifications called basidiocarps or basidiomes, or fruitbodies), variously called mushrooms, puffballs, etc. Ballistic basidiospores are formed on sterigmata which are tapered spine-like projections on basidia, and are typically curved, like the horns of a bull. In some Basidiomycota the spores are not ballistic, and the sterigmata may be straight, reduced to stubs, or absent. The basidiospores of these non-ballistosporic basidia may either bud off, or be released via dissolution or disintegration of the basidia.

In summary, meiosis takes place in a diploid basidium. Each one of the four haploid nuclei migrates into its own basidiospore. The basidiospores are ballistically discharged and start new haploid mycelia called monokaryons. There are no males or females, rather there are compatible thalli with multiple compatibility factors. Plasmogamy between compatible individuals leads to delayed karyogamy leading to establishment of a dikaryon. The dikaryon is long lasting but ultimately gives rise to either fruitbodies with basidia or directly to basidia without fruitbodies. The paired dikaryon in the basidium fuse (i.e. karyogamy takes place). The diploid basidium begins the cycle again.

Meiosis
Coprinopsis cinerea is a basidiomycete mushroom. It is particularly suited to the study of meiosis because meiosis progresses synchronously in about 10 million cells within the mushroom cap, and the meiotic prophase stage is prolonged. Burns et al. studied the expression of genes involved in the 15-hour meiotic process, and found that the pattern of gene expression of C. cinerea was similar to two other fungal species, the yeasts Saccharomyces cerevisiae and Schizosaccharomyces pombe. These similarities in the patterns of expression led to the conclusion that the core expression program of meiosis has been conserved in these fungi for over half a billion years of evolution since these species diverged.

Cryptococcus neoformans and Ustilago maydis are examples of pathogenic basidiomycota. Such pathogens must be able to overcome the oxidative defenses of their respective hosts in order to produce a successful infection. The ability to undergo meiosis may provide a survival benefit for these fungi by promoting successful infection. A characteristic central feature of meiosis is recombination between homologous chromosomes. This process is associated with repair of DNA damage, particularly double-strand breaks. The ability of C. neoformans and U. maydis to undergo meiosis may contribute to their virulence by repairing the oxidative DNA damage caused by their host's release of reactive oxygen species.

Variations in lifecycles
Many variations occur: some variations are self-compatible and spontaneously form dikaryons without a separate compatible thallus being involved. These fungi are said to be homothallic, versus the normal heterothallic species with mating types. Others are secondarily homothallic, in that two compatible nuclei following meiosis migrate into each basidiospore, which is then dispersed as a pre-existing dikaryon. Often such species form only two spores per basidium, but that too varies. Following meiosis, mitotic divisions can occur in the basidium. Multiple numbers of basidiospores can result, including odd numbers via degeneration of nuclei, or pairing up of nuclei, or lack of migration of nuclei. For example, the chanterelle genus Craterellus often has six-spored basidia, while some corticioid Sistotrema species can have two-, four-, six-, or eight-spored basidia, and the cultivated button mushroom, Agaricus bisporus. can have one-, two-, three- or four-spored basidia under some circumstances. Occasionally, monokaryons of some taxa can form morphologically fully formed basidiomes and anatomically correct basidia and ballistic basidiospores in the absence of dikaryon formation, diploid nuclei, and meiosis. A rare few number of taxa have extended diploid lifecycles, but can be common species. Examples exist in the mushroom genera Armillaria and Xerula, both in the Physalacriaceae. Occasionally, basidiospores are not formed and parts of the "basidia" act as the dispersal agents, e.g. the peculiar mycoparasitic jelly fungus, Tetragoniomyces or the entire "basidium" acts as a "spore", e.g. in some false puffballs (Scleroderma). In the human pathogenic genus Cryptococcus, four nuclei following meiosis remain in the basidium, but continually divide mitotically, each nucleus migrating into synchronously forming nonballistic basidiospores that are then pushed upwards by another set forming below them, resulting in four parallel chains of dry "basidiospores".

Other variations occur: some as standard lifecycles (that themselves have variations within variations) within specific orders.

Rusts
Rusts (Pucciniales, previously known as Uredinales) at their greatest complexity, produce five different types of spores on two different host plants in two unrelated host families. Such rusts are heteroecious (requiring two hosts) and macrocyclic (producing all five spores types). Wheat stem rust is an example. By convention, the stages and spore states are numbered by Roman numerals. Typically, basidiospores infect host one, also known as the alternate or sexual host, and the mycelium forms pycnidia, which are miniature, flask-shaped, hollow, submicroscopic bodies embedded in the host tissue (such as a leaf). This stage, numbered "0", produces single-celled spores that ooze out in a sweet liquid and that act as nonmotile spermatia, and also protruding receptive hyphae. Insects and probably other vectors such as rain carry the spermatia from spermagonium to spermagonium, cross inoculating the mating types. Neither thallus is male or female. Once crossed, the dikaryons are established and a second spore stage is formed, numbered "I" and called aecia, which form dikaryotic aeciospores in dry chains in inverted cup-shaped bodies embedded in host tissue. These aeciospores then infect the second host, known as the primary or asexual host (in macrocyclic rusts). On the primary host a repeating spore stage is formed, numbered "II", the urediospores in dry pustules called uredinia. Urediospores are dikaryotic and can infect the same host that produced them. They repeatedly infect this host over the growing season. At the end of the season, a fourth spore type, the teliospore, is formed. It is thicker-walled and serves to overwinter or to survive other harsh conditions. It does not continue the infection process, rather it remains dormant for a period and then germinates to form basidia (stage "IV"), sometimes called a promycelium. In the Pucciniales, the basidia are cylindrical and become 3-septate after meiosis, with each of the 4 cells bearing one basidiospore each. The basidiospores disperse and start the infection process on host 1 again. Autoecious rusts complete their life-cycles on one host instead of two, and microcyclic rusts cut out one or more stages.

Smuts
The characteristic part of the life-cycle of smuts is the thick-walled, often darkly pigmented, ornate, teliospore that serves to survive harsh conditions such as overwintering and also serves to help disperse the fungus as dry diaspores. The teliospores are initially dikaryotic but become diploid via karyogamy. Meiosis takes place at the time of germination. A promycelium is formed that consists of a short hypha (equated to a basidium). In some smuts such as Ustilago maydis the nuclei migrate into the promycelium that becomes septate (i.e., divided into cellular compartments separated by cell walls called septa), and haploid yeast-like conidia/basidiospores sometimes called sporidia, bud off laterally from each cell. In various smuts, the yeast phase may proliferate, or they may fuse, or they may infect plant tissue and become hyphal. In other smuts, such as Tilletia caries, the elongated haploid basidiospores form apically, often in compatible pairs that fuse centrally resulting in H-shaped diaspores which are by then dikaryotic. Dikaryotic conidia may then form. Eventually the host is infected by infectious hyphae. Teliospores form in host tissue. Many variations on these general themes occur.

Smuts with both a yeast phase and an infectious hyphal state are examples of dimorphic Basidiomycota. In plant parasitic taxa, the saprotrophic phase is normally the yeast while the infectious stage is hyphal. However, there are examples of animal and human parasites where the species are dimorphic but it is the yeast-like state that is infectious. The genus Filobasidiella forms basidia on hyphae but the main infectious stage is more commonly known by the anamorphic yeast name Cryptococcus, e.g. Cryptococcus neoformans and Cryptococcus gattii.

The dimorphic Basidiomycota with yeast stages and the pleiomorphic rusts are examples of fungi with anamorphs, which are the asexual stages. Some Basidiomycota are only known as anamorphs. Many are yeasts, collectively called basidiomycetous yeasts to differentiate them from ascomycetous yeasts in the Ascomycota. Aside from yeast anamorphs, and uredinia, aecia and pycnidia, some Basidiomycota form other distinctive anamorphs as parts of their life-cycles. Examples are Collybia tuberosa with its apple-seed-shaped and coloured sclerotium, Dendrocollybia racemosa with its sclerotium and its Tilachlidiopsis racemosa conidia, Armillaria with their rhizomorphs, Hohenbuehelia with their Nematoctonus nematode infectious, state and the coffee leaf parasite, Mycena citricolor, and its Decapitatus flavidus propagules called gemmae.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Basidiomycota


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Ascomycota

Ascomycota is a phylum of the kingdom Fungi that, together with the Basidiomycota, forms the subkingdom Dikarya. Its members are commonly known as the sac fungi or ascomycetes. It is the largest phylum of Fungi, with over 64,000 species. The defining feature of this fungal group is the "ascus", a microscopic sexual structure in which nonmotile spores, called ascospores, are formed. However, some species of Ascomycota are asexual and thus do not form asci or ascospores. Familiar examples of sac fungi include morels, truffles, brewers' and bakers' 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.

Ascomycota is a monophyletic group (containing all of the descendants of a common ancestor). Previously placed in the Basidiomycota 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 DNA sequences.

Ascomycetes are of particular use to humans as sources of medicinally important compounds such as antibiotics, as well as for fermenting bread, alcoholic beverages, and cheese. Examples of ascomycetes include Penicillium species on cheeses and those producing antibiotics for treating bacterial infectious diseases.

Many ascomycetes are pathogens, both of animals, including humans, and of plants. Examples of ascomycetes that can cause infections in humans include Candida albicans, Aspergillus niger and several tens of species that cause skin infections. The many plant-pathogenic ascomycetes include apple scab, rice blast, the ergot fungi, black knot, and the powdery mildews. The members of the genus Cordyceps are entomopathogenic fungi, meaning that they parasitise and kill insects. Other entomopathogenic ascomycetes have been used successfully in biological pest control, such as Beauveria.

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.

Sexual reproduction in ascomycetes
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 through budding.

Conidia formation
Asexual reproduction may occur through vegetative reproductive spores, the conidia. The asexual, non-motile haploid spores of a fungus, which are named after the Greek word for dust (conia), are hence also known as. The conidiospores commonly contain one nucleus and are products of mitotic cell divisions and thus are sometimes call, 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, from which the spores are produced. Not all of these asexual structures are a single hypha. 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. acervulus, 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. This is a cushion of conidiophores created from a pseudoparenchymatous stroma in plant tissue. The is a globose to flask-shaped parenchymatous structure, lined on its inner wall with conidiophores. The is a flat saucer shaped bed of conidiophores produced under a plant cuticle, which eventually erupt through the cuticle for dispersal.

Budding
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 wall. 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, forms.

Characteristics of ascomycetes

 * Ascomycota are morphologically diverse. The group includes organisms from unicellular yeasts to complex cup fungi.
 * 98% of lichens have an Ascomycota as the fungal part of the lichen.
 * 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, 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 delicacies.
 * Many of them cause tree diseases, such as Dutch elm disease and apple blights.
 * 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 mold Penicillium is used to produce the antibiotic penicillin.
 * Almost half of all members of the phylum Ascomycota form associations with algae to form lichens.
 * Others, such as morels (a highly prized edible fungi), form important relationships with plants, thereby providing enhanced water and nutrient uptake and, in some cases, protection from insects.
 * Most ascomycetes are terrestrial or parasitic. However, some have adapted to marine or freshwater environments. As of 2015, there were 805 marine fungi in the Ascomycota, distributed among 352 genera.
 * 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
There are three subphyla that are described and accepted:
 * The 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.
 * The 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.
 * The 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 hyphal fungi (Neolecta, Taphrina, Archaeorhizomyces), fission yeasts (Schizosaccharomyces), and the mammalian lung parasite Pneumocystis.

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 into the 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.

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 Hyphomycetes were 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).

Morphology
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 reproduction, many 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.

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) growth forms.

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 species.

Large masses of yeast cells, asci or ascus-like cells, or conidia can also form macroscopic structures. For example. Pneumocystis species 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.

Metabolism
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.

The 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. The 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).

Distribution and living environment
The 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
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.

Asexual spores
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.

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 Ascomycota are 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 spread them.

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 the tip),
 * blastic-synchronous (simultaneous spore formation from a central cell, sometimes with secondary acropetal chains forming from the initial spores),
 * 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 in length),
 * 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 shorter),
 * 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 arthroconidia free),
 * 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
Several 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 events.

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).

Sexual reproduction
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. Also, the adaptive basis for the maintenance of sexual reproduction in the Ascomycota fungi was reviewed by Wallen and Perlin. They concluded that the most plausible reason for the maintenance of this capability is the benefit of repairing DNA damage by using recombination that occurs during meiosis. DNA damage can be caused by a variety of stresses such as nutrient limitation.

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 red 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 1950s.

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 hyphae.

An ascocarp is the fruiting body of the sexual phase in Ascomycota. There are five morphologically different types of ascocarp, namely:

 * Naked asci: these occur in simple ascomycetes; asci are produced on the organism's surface.
 * Perithecia: Asci are in flask-shaped ascoma (perithecium) with a pore (ostiole) at the top.
 * Cleistothecia: The ascocarp (a cleistothecium) is spherical and closed.
 * Apothecia: The asci are in a bowl shaped ascoma (apothecium). These are sometimes called the "cup fungi".
 * Pseudothecia: Asci with two layers, produced in pseudothecia that look like perithecia. The ascospores are arranged irregularly.

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.

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 cylinder-shaped capsule. 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.

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.

Ecology
The 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.

Lichens
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. Mycorrhiza are 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 herbivores.

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.

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.

Plant disease interactions
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.
 * The originally Asian Cryphonectria parasitica is responsible for attacking Sweet Chestnuts (Castanea sativa), and virtually eliminated the once-widespread 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 attacks grapevines.
 * Species of 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 woolen textiles, which is a common problem especially in the tropics.
 * Blue-green, red and brown molds attack and spoil foodstuffs – for instance Penicillium italicum rots oranges.
 * Cereals infected with Fusarium graminearum contain mycotoxins like deoxynivalenol (DON), which causes Fusarium ear blight and skin and mucous membrane lesions when eaten by pigs.

Human disease interactions

 * Aspergillus fumigatus, the most common cause of fungal infection in the lungs of immune-compromised patients often resulting in death. Also the most frequent cause of Allergic bronchopulmonary aspergillosis, which often occurs in patients with Cystic fibrosis as well as Asthma.
 * 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".
 * Fungi like 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 occur in AIDS patients.
 * Ergot (Claviceps purpurea) is a direct menace to humans when it attacks wheat or rye and produces highly poisonous alkaloids, causing ergotism if consumed. Symptoms include hallucinations, stomach cramps, 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.
 * Histoplasma capsulatum causes histoplasmosis, which affects immunocompromised patients.
 * Blastomyces dermatitidis is the causal agent of blastomycosis, an invasive and often serious fungal infection found occasionally in humans and other animals in regions where the fungus is endemic.
 * Paracoccidioides brasiliensis and Paracoccidioides lutzii are the causal agents of paracoccidioidomycosis.
 * Coccidioides immitis and Coccidioides posadasii are the causative agent of coccidioidomycosis (valley fever).
 * Talaromyces marneffei, formerly called Penicillium marneffei causes talaromycosis

Beneficial effects for humans
On the other hand, ascus fungi have brought some important benefits to humanity.
 * The most famous case may be that of the mold Penicillium chrysogenum (formerly 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 treatment.
 * 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 blood clots.
 * Several species are common model organisms in biology, including Saccharomyces cerevisiae, Schizosaccharomyces pombe, and Neurospora crassa. The genomes of a number of ascomycete fungi have been fully sequenced.
 * Baker's 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.
 * Enzymes of Penicillium camemberti play a role in the manufacture of the cheeses Camembert and Brie, while those of Penicillium roqueforti do the same for Gorgonzola, Roquefort and Stilton.
 * In Asia, 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 delicacies.
 * Cordyceps militaris is known for its numerous medicinal benefits, including supporting the immune system, reducing inflammation, providing antioxidant effects, enhancing metabolic health, improving athletic performance, and promoting respiratory health. It contains bioactive compounds such as cordycepin, cordycepic acid, adenosine, and polysaccharides, beta-glucans, and ergosterol.

title: Ascomycota