A first synopsis of lichenicolous fungi of Mongolia based on new collections and literature data is provided, including 114 species. Five new species are described: Capronia cogtii (on Vahliella leucophaea), Echinothecium hypogymniae (on Hypogymnia bitteri), Feltgeniomyces mongolicus (on H. bitteri), Phacopsis vulpicidae (on Vulpicida juniperina) and Roselliniella javkhlanae (on Rinodina turfacea var. ecrustacea). Two new combinations are proposed: Endococcus hafellneri (≡ Stigmidium hafellneri) and Sphaerellothecium taimyricum (≡ Sphaerellothecium thamnoliae var. taimyricum). Unidentified specimens of Acremonium (on Mycoblastus sanguinarioides), Cercidospora (on Rhizoplaca chrysoleuca s.lat.), Didymocyrtis (on Rhizoplaca chrysoleuca s.lat.), Lichenochora (on Physcia alnophila), Lichenostigma (on species of Xanthoparmelia), Phoma (on Vulpicida juniperina) and a leotialean fungus (on Cetraria laevigata) are characterized and discussed. Taxonomic notes are provided for Cercidospora macrospora s.lat., Didymocyrtis cf. melanelixiae, Minutoexcipula cf. beaglei, Nesolechia cetrariicola, Sphaerellothecium cf. parmeliae and Stigmidium cf. psorae. Sphaeropezia intermedia is newly reported for Eurasia. Didymocyrtis grumantiana is newly reported for Asia. Additionally, 71 species of lichenicolous fungi and five species of lichenicolous lichens are documented in Mongolia for the first time. Allocetraria is reported as a new host genus for Abrothallus peyritschii, Vulpicida for Arthonia triebeliae, and Anamylopsora for Muellerella pygmaea.

Seventy-four species of lichenicolous fungi, including two species of lichenicolous lichens, are reported from Mongolia. Arthonia xanthoparmeliarum, Katherinomyces cetrariae s. lat. and Lichenochora arctica are newly reported for Asia. Arthonia epiphyscia, A. excentrica, A. molendoi, Carbonea vitellinaria, Cercidospora xanthoriae, Didymocyrtis rhizoplacae, Endococcus propinquus, Intralichen christiansenii, Lichenochora caloplacae, L. rinodinae, Lichenodiplis lecanorae, Lichenostigma dimelaenae, L. triseptatum, Niesslia peltigericola, Polycoccum trypethelioides, Rhymbocarpus neglectus, Sphaerellothecium phaeorrhizae, S. propinquellum, Stigmidium xanthoparmeliarum, Taeniolella pertusariicola and Tetramelas phaeophysciae are reported new to Mongolia. The occurrence of Stigmidium psorae in Mongolia is confirmed. Flavocetraria and Rhizoplaca are reported as new host genera for Katherinomyces cetrariae s. lat.

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Heterodermia hypoleuca (Ach.) Treis.,H. japonica (M. Sato) Swinscow & Krogand H. subascendens (Asahina) Trass. have been recorded for the first time in Mongolia. Data on substrates, habitats, distribution are listed for every species. Taxonomic comments and distinctive characters are provided for these species. The habitats are briefly described and the frequently associated species are listed. It is interesting to note that as a result of processing hundreds of herbarium collections of lichens, numerous new species were found in Mongolia. This means that there is still a substantial gap in the knowledge, especially about the lichen flora of remote corners of the country, which are numerous.

In recent years, cryptogamous biodiversity and scop their areal in Mongolia have begun to decline due to human activities, global warming and desertification, and have become one of the reasons for the threat of their extinction. At the regional level, a study was carried out to determine their conservation status in accordance with the criteria of the International Union for the Conservation of Nature and Natural Resources. First of all, according to the assessment results, 221 species (5.0%) need protection.