Based on the evidence of morphology and a comprehensive revision of herbarium collections and field records, the taxonomy of the Erigeron acris group in Murmansk Region, European Russia, is completely revised. Its accepted diversity is increased from 2 to 8 taxa, including putative hybrids. The only native species, E. politus, is distributed in mountainous regions, along sea coasts and in the Kutsa River basin. Five species are alien: E. rigidus (previously confused with E. acris s.str.), E. acris s.str. (first recorded in the narrow taxonomic definition), E. brachycephalus (previously unrecorded), E. droebachiensis and E. uralensis (previously reported in error). Two major waves of the introduction of alien taxa are discovered, with different occurrences and species compositions. Regional and local dispersal by pomors (historical Russian settlers) occurred during their colonisation and traditional activities since the 12th century (archaeophytes or early neophytes); such alien taxa (E. rigidus, E. brachycephalus, and partly E. acris) are particularly common within the territory traditionally settled by Russian colonists but also found elsewhere along historical trade routes. Other alien species of the E. acris group (E. droebachiensis, E. uralensis, and partly E. acris and E. brachycephalus) colonised industrial areas in the 1960s–1990s as seed contaminants introduced during revegetation of slag dumps, stockyards, dams and channels. Putative hybrids between E. politus (native), E. rigidus and E. acris (aliens) are found in the places of co-occurrence. Updated nomenclature, synonymy and descriptions are provided for all accepted taxa.
