The subdivision Ascomycotina (formerly the class Ascomycetes) includes all true fungi in which sexual reproduction results in ascospores, produced with in a specialized cell called an ascus. In many ascomycetes, male structures (antheridia) and female structures (ascogonia) are produced. The antheridia donate neclei to the ascogonia by fusion with a receptive filament, the trichogyne. In other the same function may be accomplished by conidia (asexual spores that can also serve as fertilizing elements) or by hyphal fussion.
The parental nuclei unite in the ascogonium and enter hyphal branches that grow out from it within a developing fruting body, the ascocarp. The paired parental nuclei divide synchronously (conjugate division) in specialized hyphae with binucleate cells (ascogenous hyphae). The tip cells of the ascogenous hyphae from a hock in which the haploid parental nuclei fuse to produce a diploid zygote nucleus. Undergoes neiotic divisions to produce four haploid nuclei in the enlarging cell, called the ascus at this stage of development. In most cases a mutotoc nuclear division then doubles the number of nuclei per ascus, after which each nucleus is enclosed in a cell wall to form the ascospores.
Other major feature of ascomycetes exist. The class Hemiascomycetes includes the Yeasts; these may be unicellular or mycelial, but all lack ascogenous hyphae and fruits. Most yeast are saprobic, commonly occurring on plant parts, in soil, and in other locations with adequate moisture and organic material. A small group is parasitic on the leaves, twigs, and branches of vascular plants, causing leaf curl and witches broom (tufts of branches resulting from repeated branching).
Other Fungi Subdivisions:
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