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 2019 on field time study in Mongolian-Altai heigh mountain steppe region we collected 120 lichen samples from different substratum in heigh mountain area (altitude: 2527-2770 m). We identified some interesting species such as Buellia geophila (Florke ex Sommerf.) Lynge, Caloplaca cerina (Ehrh. Ex Hedw.) Fr., Diploschistes diacapsis (Ach.) Lumbsch., Rinodina mniaraea (Ach.) Korrb., Vulpicida tubulosus (Schaer) J.E.Mattsoon & M.J.Lai, Caloplaca crenulatella (Nyl.) H.Oliver and Phaeophyscia squarrosa Hale. These species firstly recorded in the Mongolian Altai mountain steppe region. Монгол-Алтайн уулын хээрийн тойрогт тэмдэглэсэн 7 зүйл хагийн шинэ цэгүүд Хураангуй. Манай орны хуурай гандуу уулархаг нутгийн хүрээнд тусгайлан тодорхой газар нутгийн хагийн аймгийг тусад нь судалсан судалгаа огт хийгдээгүй ирсэн. Иймд уур амьсгалын өөрчлөлтийн сөрөг нөлөөгөөр байгалийн аясаар нөхөн сэргэх чадвар хязгаарлагдмал хагийн төрөл зүйлүүдийн олон янз байдалд чухал амьдрах орчинг хагаар тогтоох зорилгоор 2019 онд хэрэгжүүлсэн хээрийн судалгааны үр дүнд Монгол орны ургамал газарзүйн Монгол-Алтайн өндөр уулын хээрийн тойрогт Buellia geophila (Florke ex Sommerf.) Lynge; Caloplaca cerina (Ehrh. ex Hedw.) Th. Fr.; Diploschistes diacapsis (Ach.) Lumbsch.; Rinodina mniaraea (Ach.) Korrb.; Vulpicida tubulosus (Schaer) J.E. Mattsoon &M.J. Lai; Caloplaca crenulatella (Nyl.) H.Oliver болон Phaeophyscia squarrosa Hale. гэсэн 7 зүйлийн тархацын шинэ цэгийг бүртгэв. Түлхүүр үгc: Хаг биот, тархацын цэг, Caloplaca crenulatella.