Ascomycetes are a group of fungi known for their unique reproductive structure called the ascus, which produces spores. These fungi can be found in various environments, from soil to decaying wood, and they play essential roles in ecosystems, such as decomposing organic matter. Some Ascomycetes are also important in food production, like yeast used in baking and brewing. Many Ascomycetes are beneficial, but some can cause diseases in plants and animals. For example, the fungus Aspergillus can lead to respiratory issues in humans. Overall, Ascomycetes are a diverse and vital part of the fungal kingdom, contributing to both nature and human industry.