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The Carpathians are the largest mountain range in Central Europe. Their geographical position, extent, isolation, landscape heterogeneity, well-preserved environment, and relatively low impact of Quaternary glaciations make them of utmost importance for studies on European biodiversity and biogeography. In this review, introducing a Special Issue of the Biological Journal of the Linnean Society, we provide an overview of current research and focus on three main aspects: (1) distribution patterns and species richness including endemism; (2) phylogeographical patterns, inference of major barriers, and divergence areas; and (3) cytological studies and cytogeography inferred from vascular plant polyploid complexes. Our survey shows that, although accurate estimation is not possible for several important taxonomic entities because of unavailable or dispersed data, the Carpathians are a clear hotspot of European diversity for many groups of organisms, such as mammals, breeding birds, amphibians, lichens, and vascular plants. Certain groups, not necessarily those with high species richness, are rich in endemic taxa. This holds mainly for subterranean invertebrates, molluscs, grasshoppers, beetles, spiders, and vascular plants. Distribution patterns of endemic richness vary across taxonomic groups, as well as geographically, reflecting both history and habitat features. In general, the South-Eastern Carpathians have a significantly higher proportion of endemic taxa than the northerly-situated Western Carpathians. Molecular clock-based estimations have provided some insight into the diversification age of the Carpathian biota, including a Tertiary origin for some endemic taxa and lineages, especially those confined to environmentally stable habitats. Distribution patterns, as well as phylogeographical and phylogenetic data, corroborate the persistence of many high-mountain and forest taxa during the Quaternary climatic oscillations, often in multiple spatially delimited areas isolated by physical barriers. Several studies show that the Carpathian massifs played an important role as refugia for rare lineages and/or as stepping stones in migrations. Phylogeographical analysis reveals clear patterns of biogeographical breaks, as well as links, although clear exceptions also confirm that extant distribution patterns are often shaped more by idiosyncratic processes acting at different geological times. Cytogeographical data also uncover several consistent patterns, which probably reflect a deeper evolutionary history. In conclusion, the available data highlight the unique position of the Carpathians in the evolution and preservation of European biota within the European Alpine System. [ABSTRACT FROM AUTHOR]

DNA ploidy levels were estimated using DAPI-flow cytometry of silica-dried specimens of the European mountain plant Senecio carniolicus (Asteraceae), covering its entire distribution area in the Eastern Alps (77 populations, 380 individuals) and the Carpathians (five populations, 22 individuals). A complex pattern of ploidy level variation (2x, 4x, 5x, 6x, and 7x cytotypes) was found in this species, which has been considered uniformly hexaploid. Hexaploids predominated in the Eastern Alps and was the only cytotype found in the Carpathians, while odd ploidy levels (5x, 7x) constituted a small fraction of the samples (<1.3%). Tetraploids occurred in two disjunct areas, which correspond with putative Pleistocene refugia for silicicolous alpine plants. Diploids occurred in large portions of the Alps but were absent from areas most extensively glaciated in the past. Intrapopulational cytotype mixture was detected in 22 populations—the majority involving diploids and hexaploids—with intermediate ploidy levels mostly lacking, suggesting limited gene flow and the evolution of reproductive isolation. Significant and reproducible intracytotype variation in nuclear DNA content was observed. Higher genome size in western diploids might be due to ancient introgression with the closely related S. incanus or to different evolutionary pathways in the geographically separated diploids. [ABSTRACT FROM AUTHOR]