The hyphae (“fungus threads”) of Ascomycota are compartmentalised by septs. Moreover the hyphae can form a dense three-dimensional lattice that in form and structure resembles the parenchyma of plants. This enables these fungi to form three-dimensional structures, for instance in connection with the reproduction.
Both sexual and asexual reproduction do occur in the Ascomycota, and most species apply both strategies. The commonest form of asexual reproduction is by way of conidia: spores that are derived by budding of the end of an hypha. They are formed on specialised hyphae: conidiophores. Conidia may be one- or more-celled, and can have a wide variety of shapes and structures.
In principle hyphae are haploid. By various forms of sexuality a diploid piece of hypha may be formed, that develops into a sac-like structure which is called an ascus. In the ascus meiosis occurs, followed by a mitosis resulting in eight haploid nuclei, around which then eight ascospores differentiate. The development of asci generally takes place in specialised fruiting bodies, that may be disc-shaped or hollow, and then sunken more or less deeply into the substrate. The details of the asci and the fruiting bodies are the main characters upon which the classification of the Ascomycota is based.
The asexual phase of many species (the anamorph) is known, but not the sexual phase (the telomorph – that even may not exist at all); it is not possible then to know their systematic place. They are named “Deuteromycota” or “Fungi Imperfecti”. Molecular techniques have shown that most belong to the Ascomycota; only a minority belong to the Basidiomycota.
Alexopoulos, Mims & Blackwell (1996a).