The class Leotiomycetes is a diverse group of fungi within the phylum Ascomycota, characterized by the production of their sexual spores (ascospores) inside sac-like structures called asci, which are usually contained in small, disk- or cup-shaped fruiting bodies known as apothecia. Members of this class include both saprobes, which decompose plant material, and important plant pathogens, such as those causing powdery mildew and various leaf spot diseases. They are widespread in terrestrial ecosystems and play key roles in nutrient cycling, symbiosis, and disease dynamics. Economically and ecologically, Leotiomycetes are significant because they impact agriculture, forestry, and natural plant communities.