The Class Ascomycetes (or Sac fungi) is a large group of fungi characterized by producing spores in a sac-like structure called an ascus. They include yeasts, morels, truffles, and many plant pathogens. Ascomycetes can be unicellular or multicellular, reproduce sexually through ascospores and asexually via conidia, and play key roles in decomposition, fermentation, and biotechnology. They are ecologically and economically important, contributing to nutrient cycling, food production, medicine (e.g., antibiotics), and disease.