Alpine endemic species are great study systems to infer the influence of Pleistocene glaciation on evolution and distribution of mountain plants. A particularly well-suited group is Galium (Rubiaceae). This genus is represented by 46 species in the Alps, ten of which are endemic to this mountain range. Many of the widespread Galium species show big variation in morphological characters and ploidy level, which renders it difficult to assess their relationships to range-restricted species that

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... be anything from clearly distinct species to mere ecotypes of widespread species. In this study, phylogenetic relationships of two endemics from the north-eastern Alps – the diploid G. truniacum and the tetraploid G. meliodorum – to the tetraploid, but widespread G. lucidum are investigated. Thus, we test the hypothesis, implied by current taxonomy, that each of these species represents a distinct lineage, separated from each other by ploidy (diploid G. truniacum versus tetraploid G. meliodorum and G. lucidum) and/or by ecology (high elevation G. meliodorum versus low elevation G. lucidum). Applying RAD-sequencing data on individuals with known ploidy, determined using flow-cytometry, we found a clear separation into two groups corresponding to ploidy level, but no separation within the tetraploid group. The strong morphological and ecological differentiation between the two tetraploids might be due to few adaptive loci or elevated phenotypic plasticity. Additionally, we found signals of shared ancestry between ploidy levels. Therefore, a re-evaluation of the taxonomic status of G. meliodorum is proposed.