With nearly 90,000 species, Ascomycota is the largest division in the kingdom Fungi. Species of the division are also referred to as Ascomyetes or sac-fungi. Ascomycota, together with Basidiomycota, comprises the subkingdom Dikarya. The famous and sought-after morels and truffles are ascomycetes, as well as cup fungi, earth tounges, and some yeasts.
Types of Ascomycetes
- Cup Fungi
- Earth Tounges
Division or Phylum?
According to my research, a phylum refers to the Kingdom Animalia as where division refers to Kingdoms Fungi and Plantae. However, it is only semantics, both terms essentially mean the same thing.
Multicellular ascomycetes can reproduce sexually and asexually. They form fruiting bodies called ascocarps. The spore-bearing tissue of ascocarps, known as hymenium, contains sac-like cells called asci the produce ascospores. Cup-shaped ascocarps that constantly expose their hymenium are known as apothecium.
Multicellular Sexual Reproduction Cycle
During sexual reproduction, two spores of different mating types (plus and minus) will germinate and produce haploid hyphae. The septated hyphae will branch out in search of the opposite mating type. When the two types meet, they fuse in plasmogamy; the process results in dikaryotic hyphae that contain two nuclei. The progeny of the dikaryotic hyphae also contain two nuclei and will continue to branch off. Eventually, at the tip of a dikaryotic hypha, karyogamy will occur. In karyogamy, the two nuclei will fuse, forming a zygote. The cell will also develop a protective sac-like container called an ascus (hence: sac-fungi). In the next stage, the cell will go through meiosis, dividing twice to produce four cells with half the number of chromosomes. Then the cell will go through mitosis where each cell divides again, developing eight haploid spores, called ascospores. With maturity, the ascus ruptures releasing the ascospores, and the cycle continues.
Multicellular Asexual Reproduction Cycle
During asexual reproduction, the tips of specialized stalk-like hyphae, called conidiophores, develop conidia (spores).
Unicellular Asexual Reproduction
Microscopic unicellular species like yeasts typically reproduce asexually by budding or fission. In budding, a cell's haploid nucleus will divide by mitosis. The parent cell forms an outgrown or bud. One of the daughter nuclei will migrate into the bud. Eventually, the bud will then enlarge, wall off, and detach from the parent cell. The daughter cell then matures into a new yeast cell.
In fission, a cell's haploid nucleus will also divide by mitosis, but then the parent cell will split into two halves. Finally, both cells will grow into parent cells.
Unicellular Sexual Reproduction
Some yeast cells reproduction sexually. When yeast of different matting types collide, they will begin conjugation and fuse together. The haploid nuclei will also fuse, resulting in a new diploid nucleus. Budding then occurs, forming a new diploid daughter cell. The new cell could then reproduce sexually (budding or fission), or the cell will undergo meiosis. In meiosis, the cell will form an ascus, and four haploid ascospores will develop inside. When the ascus matures, it will rupture, and the four ascospores will release to continue the process anew.
Subdivisions & Classes of Ascomycota
Taphrinomycotina is a subdivision of Ascomycota containing plant pathogens and yeasts. The Pneumocystidales class contains yeast that causes a form of pneumonia in mammals.
Classes of Taphrinomycotina
Saccharomycotina is a subdivision of Ascomycota containing many economically essential yeasts. Baker's yeast belongs to this subdivision, as well as yeasts used in the fermentation of beverages (beer & wine) and foods, the production of biofuels, citric acid, and more. However, some species are responsible for plant pathogens that devastate yields of cash crops. Yeasts in this subdivision are also known to cause contamination to food and beverages, while others contain human pathogens found in the genus Candida.
Classes of Saccharomycotina
Pezizomycotina is the largest subdivision of Ascomycota containing over 30,000 known species (total estimate is over 100,000 species). All ascomycetes in the Pezizomycotina subdivision produce ascocarps. Many ascomycetes with visible fruiting bodies comprise this subdivision, such as cup fungi, morels, truffles, earth tongues, and lichen.
Classes of Pezizomycotina
- Encyclopedia Britannica: Ascomycota
- YouTube: Ascomycota
- State of the World's Fungi 2018
- Wikipedia: Ascomycota