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Aim The objective of this study was to analyse the data represented by 1976 specimens of myxomycetes collected in high-latitude regions of the Northern Hemisphere to obtain information on the biogeographical relationships and patterns of occurrence of these organisms. The question of what factors limit myxomycete distribution in high-latitude and cold-dominated regions was also addressed.Location Specimens of myxomycetes considered herein were collected from twelve study areas in Iceland, northern Russia and Alaska, and Greenland. The vast majority of specimens were collected during the period of 1989-98.Methods Nine hundred and thirty-three specimens were recorded as field collections. In addition, 1043 specimens originated from moist chamber cultures prepared with 1453 substratum samples collected in the various study areas. From a database recording the type of substratum (wood, bark of living trees, litter or dung) for each specimen, patterns of substratum occurrence for particular species of myxomycetes in high-latitude regions were determined.Results From the 150 species recorded for the twelve study areas, thirty-three were found to be widely distributed (recorded from at least five study areas), and only fortyone had a frequency of occurrence higher than 1% either in moist chambers or as field collections. These data were examined in an effort to identify possible factors limiting the distribution of myxomycetes in high-latitude regions.Main conclusions Upon first inspection, the arctic and subArctic myxomycete biota seems to be a depauperate version of that of temperate and boreal regions. However, a few species elsewhere recorded as rare but found to be fairly common in this study indicate that a certain degree of distinctiveness exists in Arctic and subArctic myxomycetes.

The myxomycetes (plasmodial slime molds or myxogastrids) are a group of eukaryotic microorganisms usually present and sometimes abundant in terrestrial ecosystems. Evidence from molecular studies suggests that the myxomycetes have a signiWcant evolutionary history. However, due to the fragile nature of the fruiting body, fossil records of the group are exceedingly rare. Although most myxomycetes are thought to have very large distributional ranges and many species appear to be cosmopolitan or nearly so, results from recent studies have provided evidence that spatial distribution patterns of these organisms can be successfully related to (1) diVerences in climate and/or vegetation on a global scale and (2) the ecological diVerences that exist for particular habitats on a local scale. A detailed examination of the global distribution of four examples (Barbeyella minutissima, Ceratiomyxa morchella, Leocarpus fragilis and Protophysarum phloiogenum) demonstrates that these species have recognizable distribution patterns in spite of the theoretical ability of their spores to bridge continents.

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