The Hysteriales is an order

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...

 of fungi in the class 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...

, subclass Pleosporomycetidae

Pleosporomycetidae

Pleosporomycetidae is a subclass of Dothideomycetes consisting of four orders: Pleosporales, Hysteriales, 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...

. It consists of a single family

Family (biology)

In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

, Hysteriaceae

Hysteriaceae

The Hysteriaceae is a family of fungi in the order Hysteriales. They are characterised by having sexual structures called hysterothecia, an elongated structure that opens by a longitudinal slit and releases the sexually produced spores...

. Members of Hysteriales produce elongated, often boat shaped sexual structures with slit-like openings (hysterothecia). However species with these structures are very diverse. Comparisons based on 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...

 sequences indicate species with hysterothecia do not share a single ancestor

Monophyly

In common cladistic usage, a monophyletic group is a taxon which forms a clade, meaning that it contains all the descendants of the possibly hypothetical closest common ancestor of the members of the group. The term is synonymous with the uncommon term holophyly...

and therefore species with hysterothecia can be found in several fungal orders. The newest definition of the order relies on DNA sequence differences and a combination of morphological characters.