| Summary: | Variability or variation of syntaxons of Arctic is seen as a change in their floristic composition, biomorphic set and structure types when the geographic location and environmental conditions are change. This problem is solved within the framework of the notions of geographical variability of syntaxon in different types of areals, which have a rank structure. Examples of local, regional and major associations are considered. The formation of a geographical association is determined by two groups of factors: the process of phylogenesis and major changes in the physio-geographical environment occurring in the geological past. Often the variation of the floristic composition of the syntaxon in the Arctic and the associated biomorphic composition is determined not by geographic, but by ecological causes. The same species (ecologically differentiating) can enter into diagnostic groups of associations whose communities occupy different types of habitats. The study of the variation of different parameters of the Arctic syntaxa, which was recently designated as a comparative syntaxonomy, showed that for both the floral composition, and for the biomorphic and horizontal structure, their specific set within a given syntaxon is crucial. Together they characterize the association as a stable type in terms of geographical variation and allow us to outline possible ways of studying the historical formation of certain types of communities.
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