| Summary: | Glaciers are rather unusual habitat for mosses, but sometimes they can be suitable for some species due to presence of sufficient moisture and cryoconite substrate in the ablation zone. To date, moss populations were found only on a few glaciers in Alaska, Iceland and Svalbard. An origin and development of moss cushions on ice (so called "glacier mice") are still unclear. In this study, some aspects of the moss population development were explored on ice of the Svalbard glaciers – Bertilbreen (Billefjorden) and Austre Grnfjordbreen (Grnfjorden) in 2012 and 2013. On Bertilbreen, populations of Hygrohypnella polaris (Lindb.) Ignatov & Ignatova and Schistidium abrupticostatum (Bryhn) Ignatova & H.H. Blom were found for the first time. Due to putative morphological features, identification of S. abrupticostatum was confirmed by com-paring ITS1-2 nrDNA sequence data to BLAST searches (megablast). The results indicated a genetic heterogeneity of the population. Although visually moss-free, examination of cryoconite sediments revealed development of new individuals of S. abrupticostatum from filamentous structures consisting of caulonema and rhizoids. The developmental stages of young plants were revealed. Therefore, besides fragmen-tation of existing cushions, cryoconite sediments provided a source of new moss cush-ions in glacier populations. Additionally a few plants of Pohlia cf. wahlenbergii (F. Weber & D. Mohr) Andrews and a gametophyte fragment of Philonotis sp. were found in aggregation of cryoconite. Presence of Paludella squarrosa (Hedw.) Brid. reported for Bertilbreen has not been confirmed. On Austre Grnfjordbreen Bryum cryophilum Mrtensson, Sanionia uncinata (Hedw.) Loeske were found invading into some Hygrohypnella polaris cushions. Each moss polster on ice represents a separate mini-ecosystem that includes successive colonization events.
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