Myxomycetes are microorganisms frequently considered to be of cosmopolitan distribution, however as studies in unexplored areas have intensified, more information has become available on the patterns of distribution of these organisms, but no historical or cladistic biogeographic approaches have been applied to understand such patterns. In this study a parsimony analysis of endemicity (PAE) was used in order to generate a preliminary hypothesis on the biogeographic relationships of 13 American areas in which a well-known myxomycete biota exists. In general terms the hypotheses of the relationship between the myxomycete assemblages of areas used in this study agree with those reported for other groups of organisms. They appear to show that a historical-geographic pattern influences the distribution of myxomycetes as much as environmental factors. Three main clades were found in the analysis, with the first one including the two subantarctic localities, the second one representing the South American transition zone and the last one including all the Neotropical and Nearctic areas, but arranged into two subclades, one with the arid areas and the other with the tropical and temperate humid areas. Each clade or subclade in the cladogram is supported by the presence of several morphospecies, some of which appear to represent endemic species restricted to specific geographic areas. The results of this analysis are proposed as a working hypothesis that can perhaps be supported in the future with new data from other complementary regions of America or with more intense surveys in the areas already explored. They are inconsistent with the hypothesis of cosmopolitan distribution for these microorganisms, as they appear to indicate groups of species that are restricted to certain geographic areas, some of which may be endemic, such as those from the subantarctic forests of South America, those found exclusively in the South American arid areas or those that have been recently described from arid areas of North America.