Fungi, producing the spores formed by sexual reproduction in tubular structures (asci).
Many of the 30 000 ascomycetes are simple saprophytes like yeasts (Saccharomyces) and moulds. Typical examples are members of the genus Aspergillus producing toxic aflatoxins and causing severe diseases of humans and animals. Members of the genus Penicillium, in contrast, are more or less harmless and are used for the production of antibiotics (Penicillin) and for the production of a number of cheese varieties (Penicillium roquefortii, Penicillium camemberti). Further well-known members are important plant pathogens like the Erysiphales, causing mildew or Claviceps purpurea causing ergot. Most fungal partners of lichens are belonging to the ascomycetes as well, the same as some important edible mushrooms like morels (Morchella) and truffles (Tuber).