Pleosporomycetidae is a subclass of Dothideomycetes

Dothideomycetes

Dothideomycetes is the largest and most diverse class of ascomycete fungi. It comprises 11 orders 90 families, 1300 genera and over 19,000 known species. Traditionally, most of its members were included in the loculoascomycetes, which is not part of the currently accepted classification...

 consisting of four orders

Order (biology)

In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

: Pleosporales

Pleosporales

The Pleosporales is the largest order in the fungal class Dothideomycetes. By some estimates it contains 23 families, 332 genera and more than 4700 species. The majority of species are saprobes on decaying plant material in fresh water, marine, or terrestrial environments, but several species are...

, Hysteriales

Hysteriales

The Hysteriales is an order of fungi in the class Dothideomycetes, subclass Pleosporomycetidae. It consists of a single family, Hysteriaceae. Members of Hysteriales produce elongated, often boat shaped sexual structures with slit-like openings . However species with these structures are very diverse...

, Mytilinidiales and Jahnulales. One of its defining features is the presence of pseudoparaphyses. These are sterile cells extending down from the upper portion of the cavity inside sexual structures containing the sac-like asci

Ascus

An ascus is the sexual spore-bearing cell produced in ascomycete fungi. On average, asci normally contain eight ascospores, produced by a meiotic cell division followed, in most species, by a mitotic cell division. However, asci in some genera or species can number one , two, four, or multiples...

 with sexually produced spores (ascospores). Pseudoparaphyses are initially attached at both their ends, but sometimes the upper part may become free. Some orders and families where these cells are present remain outside of the subclass since DNA

DNA

Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...

 based phylogenies cannot place them with confidence. However they could conceivably be included within Pleosporomycetidae in future.