It is the largest group of fungi, including over 60,000 species, 50% or so occurring in lichens and some, such as morels are mycorrhizal.
Most are terrestrial, though some are marine or fresh water.

The group shows diversity from unicellular yeast to large cup fungi and morels.
They produce haploid sexual spores called ascospores by meiosis inside their characteristics sac like structures called asci.
Meiosis follows nuclear fusion inside the ascus, commonly 8 ascospores, inside each ascus.
Most sac-fungi have asci inside macroscopic fruiting bodies called ascocarps the visible morels etc.

heir hyphae are septate.
They have lengthy dikaryotic hypae that from ascocarps.
They reproduce asexually by conidia that are often dispersed by wind.
Yeasts are unicellular microscopic fungi, derived from all the three different groups of fungi but mostly Ascomycetes, and reproducing mostly asexually by budding. However yeasts reproduce sexually by forming ascospores or basidiospores.they ferment carbohydrate to ethanol and carbon dioxide. Because of this feature and many other reasons, these are great economic importance.