An order of ascomycetous fungi of parasitic or saprophytic habit, with the tissues usually hard and somewhat coriaceous.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
noun.
class of fungi in which the fruiting body is a perithecium; includes powdery mildews and ergot and Neurospora
Word Usage
"Those which vegetate most luxuriantly there are the _fungi_, and among them especially the _pyrenomycetes_, which are frequent in the waters of mines."