class of more than 6,000 species of sac fungi in the phylum Ascomycota (kingdom Fungi) characterized by a flask-shaped fruiting body (perithecium) that bears saclike structures (asci) and usually has a pore (ostiole) through which ascospores are discharged. Genera that parasitize higher plants include Hypoxylon, which produces tree cankers; Gnomonia (leaf spots); Diaporthe (stem and leaf blights); Endothia (chestnut blight), Claviceps (ergot of rye); and those of the powdery mildew fungi. Fungal genetics have been extensively studied in Neurospora and Glomerella.