Polyploidy is one of the major forces of plant evolution and widespread mixed-ploidy species offer an opportunity to evaluate its significance. We therefore selected the cosmopolitan species Urtica dioica (stinging nettle), examined its cytogeography and pattern of absolute genome size, and assessed correlations with bioclimatic and ecogeographic data (latitude, longitude, elevation). We evaluated variation in ploidy level using an extensive dataset of 7012 samples from 1317 populations covering most of the species' distribution area. The widespread tetraploid cytotype (87%) was strongly prevalent over diploids (13%). A subsequent analysis of absolute genome size proved a uniform Cx-value of core U. dioica (except for U. d. subsp. cypria) whereas other closely related species, namely U. bianorii, U. kioviensis and U. simensis, differed significantly. We detected a positive correlation between relative genome size and longitude and latitude in the complete dataset of European populations and a positive correlation between relative genome size and longitude in a reduced dataset of diploid accessions (the complete dataset of diploids excluding U. d. subsp. kurdistanica). In addition, our data indicate an affinity of most diploids to natural and near-natural habitats and that the tetraploid cytotype and a small part of diploids (population from the Po river basin in northern Italy) tend to inhabit synanthropic sites. To sum up, the pattern of ploidy variation revealed by our study is in many aspects unique to the stinging nettle, being most likely first of all driven by the greater ecological plasticity and invasiveness of the tetraploid cytotype.

Department of Botany Faculty of Science Charles University Prague Czech Republic

Department of Botany Faculty of Science University of South Bohemia České Budějovice Czech Republic

Faculty of Environmental Sciences Czech University of Life Sciences Prague Prague Czech Republic

Institute of Botany The Czech Academy of Sciences Průhonice Czech Republic

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New estimates and synthesis of chromosome numbers, ploidy levels and genome size variation in Allium sect. Codonoprasum: advancing our understanding of the unresolved diversification and evolution of this section

Diploid and tetraploid cytotypes of the flagship Cape species Dicerothamnus rhinocerotis (Asteraceae): variation in distribution, ecological niche, morphology and genetics

Morphological and environmental differentiation as prezygotic reproductive barriers between parapatric and allopatric Campanula rotundifolia agg. cytotypes

Morphological, ecological and geographic differences between diploids and tetraploids of Symphytum officinale (Boraginaceae) justify both cytotypes as separate species

Intricate Distribution Patterns of Six Cytotypes of Allium oleraceum at a Continental Scale: Niche Expansion and Innovation Followed by Niche Contraction With Increasing Ploidy Level