General characters of Ascomycotina:
The fallowing are important characters of the sub-division Ascomycotina.
- The members vary in their form and structure. Yeasts are unicellular, but mostly they have well developed, profusely branched and septate mycelium with uni or multinucleate cells and perforated septa.
- In unicellular forms, the cell wall is composed of glucans and mannans, whereas in septate forms it consists of chitin and glucans.
- Asexual reproduction takes place by various types of non-motile spores, such as oidia, chlamydospores and conidia. In unicellular forms, fission,fragmentation and budding are the most common methods of vegetative propagation.
- They are homothallic or heterothallic. In some heterothallic species, though male(antheridium) and female(ascogonium) sex organ develop on the thallus of the same strain they are self incompatible. In these species male gamet of one mating type fertilises ascogonium of other mating type. This process is known as physiological heterothallism.
- Sexual reproduction takes place by gametangial copulation(e.g., yeast), gametangial contact(e.g., Aspergillus), somatogamy(e.g., Morchella) or spermatization(e.g., Polystigma).
- They show the phenomenon of heterokaryosis, i,e., the nuclei of two different genotypes are present in the same mycelium.
- The fruiting bodies are known as ascocarp. The following four types of fruiting bodies are found:
b) Perithecium: It is a flask shaped structure in which asci develop from the inner surface of the fruiting body. It has an apical pore, known as ostiole. Hair like sterile paraphysis are present on the neck and mouth of the fruiting body, e.g., Claviceps.
c) Cleistothecium: It is globose and completely closed fruiting body in which asci are scattered, e.g., Phyllactinia, Aspergillus, Penicillium.
d) Ascostroma: It is a pseudoparenchymatous structure composed of somatic hyphae. The fruiting body lacks a distinct wall and asci are usually bitunicate.
8. The ascospores are endogenous in origin.