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Why yeast is placed in Ascomycota group of kingdom fungi?

he unifying characteristic among these diverse groups is the presence of a reproductive structure known as the ascus, though in some cases it has a reduced role in the life cycle.

Like basidiomycota, most ascomycota sprout from spores into hapliod mycelia. These mycelia can produce two types of reproductive structures. First, they can produce conidiophores for asexual reproduction. Conidiaphores may simply branch off from the mycelia or they may be formed in fruiting bodies. Secondly, ascomycota produce structures for sexual reproduction called gametangia. These structures are either male or female. The male gametangia may be anything from a detached cell (called a spermatium) to a differentiated region called an antheridium. The female structure is always a differentiated region known as the ascogonium. Many Ascomycota form a fruiting body, or ascoma, similar to that of the Basidiomycota, but with an important difference. The ascomycota fruiting body is composed mainly of entangled monokaryotic hyphae from the male and female mycelia rather than of dikaryotic hyphae formed from the joining of hyphae from the two mycelia, as in the basidiomycota. The only dikaryotic structures in the fruiting body are those produced by the gametangia after plasmogamy.

The exceptions to the above discussion of structure are the unicellular ascomycota or yeasts. These organisms are non-motile single cells with chitinous cell walls that earn them classification as fungi. Though they mainly reproduce by budding and fission, yeasts also engage in sexual reproduction that results in the production of an ascus, placing them in the Ascomycota. Most varieties of yeast do not form multicellular filiments like the mycelia and hyphae of other fungi, though they do live in massive groupings called colonies.