A class of the *Ascomycotina
containing those ascomycetes that produce a *cleistothecium
. It numbers about 2300 species in some 160 genera. It is not a natural class as it contains both fungi with single-walled asci and others with double-walled asci. Also some are primitive while others are regressive. It contains the orders Ascophaerales, *Eurotiales
, and Meliolales.