The members of class ascomycetes of the kingdom Fungi are commonly known as 'sac-fungi', they are mostly multicellular (e.g., Penicillium) but some unicellular forms (e.g., Saccharomyces) are also found. They are decomposers, saprophytic, parasitic or coprophilous and have a branched and septate mycelium. Conidia are the exogenously produced asexual spores and these conidia on germination produce mycelium. Ascospores are the sexual spores which are produced endogenously in sac like asci. E.g., morels and truffles are edible delicacies, Neurospora (extensively used in biochemical and genetic work), Claviceps.