Eurotiomycetes is a large class of ascomycetes with cleistothecial ascocarps within the subphylum Pezizomycotina, currently containing around 3810 species according to the Catalogue of Life. It is the third largest lichenized class, with more than 1200 lichen species that are mostly bitunicate in the formation of asci. It contains most of the fungi previously known morphologically as "Plectomycetes". Systematics and phylogeny Internal relationships The class Eurotiomycetes was circumscribed in 1997 by Swedish mycologists Ove Erik Eriksson and Katarina Winka. At that time it only contained the order Eurotiales, which together with the next order added, Onygenales, form a monophyletic group comprising most of the fungi in "Plectomycetes", a group no longer in use that unified fungi under exclusively morphological characteristics. As more orders were added to Eurotiomycetes, the first two along with Arachnomycetales became constrained to the first subclass, Eurotiomycetidae. In 2001, the second subclass, Chaetothyriomycetidae, was erected to accommodate Chaetothyriales and its sister group Verrucariales, as well as Pyrenulales since 2004. These two remain as the major subclasses of Eurotiomycetes. The remaining subclasses were created through more phylogenetic analyses to accommodate outlying taxa or newly discovered groups: Mycocaliciomycetidae in 2007, Coryneliomycetidae and Sclerococcomycetidae in 2016, and lastly Cryptocaliciomycetidae in 2021. The following cladogram shows the relationships between all Eurotiomycetes orders and monotypic subclasses as of 2021: External relationships The class Eurotiomycetes forms a clade with Lecanoromycetes, the largest lichenized class of fungi. Taxonomy As of 2022, the taxonomy of Eurotiomycetes recognizes 5 subclasses, 10 orders, 34 families and 289 valid genera. The families are listed here followed by the number of genera. Subclass Chaetothyriomycetidae Order Chaetothyriales Family Chaetothyriaceae – 19 genera Family Coccodiniaceae – 4 genera Family Cyphellophoraceae – 2 genera Family Epibryaceae – 1 genus Family Herpotrichiellaceae – 17 genera Family Lyrommataceae – 1 genus Family Microtheliopsidaceae – 1 genus Family Paracladophialophoraceae – 1 genus Family Pyrenotrichaceae – 2 genera Family Trichomeriaceae (=Strelitzianaceae ) – 9 genera Chaetothyriales incertae sedis – 11 genera Order Phaeomoniellales Family Celotheliaceae (=Phaeomoniellaceae ) – 11 genera Order Pyrenulales Family Pyrenulaceae – 12 genera Pyrenulales incertae sedis – 2 genera Order Verrucariales Family Adelococcaceae – 3 genera Family Sarcopyreniaceae – 1 genera Family Verrucariaceae – 52 genera Verrucariales incertae sedis – 4 genera Chaetothyriomycetidae incertae sedis Family Rhynchostomataceae – 2 genera Subclass Cryptocaliciomycetidae Order Cryptocaliciales Family Cryptocaliciaceae – 1 genus Subclass Coryneliomycetidae Order Coryneliales Family Coryneliaceae – 8 genera Family Eremascaceae – 2