The factors that promote invasive behavior in introduced plant species occur across many scales of biological and ecological organization. Factors that act at relatively small scales, for example, the evolution of biological traits associated with invasiveness, scale up to shape species distributions among different climates and habitats, as well as other characteristics linked to invasion, such as attractiveness for cultivation (and by extension propagule pressure). To identify drivers of invasion it is therefore necessary to disentangle the contribution of multiple factors that are interdependent. To this end, we formulated a conceptual model describing the process of invasion of central European species into North America based on a sequence of "drivers." We then used confirmatory path analysis to test whether the conceptual model is supported by a statistical model inferred from a comprehensive database containing 466 species. The path analysis revealed that naturalization of central European plants in North America, in terms of the number of North American regions invaded, most strongly depends on residence time in the invaded range and the number of habitats occupied by species in their native range. In addition to the confirmatory path analysis, we identified the effects of various biological traits on several important drivers of the conceptualized invasion process. The data supported a model that included indirect effects of biological traits on invasion via their effect on the number of native range habitats occupied and cultivation in the native range. For example, persistent seed banks and longer flowering periods are positively correlated with number of native habitats, while a stress-tolerant life strategy is negatively correlated with native range cultivation. However, the importance of the biological traits is nearly an order of magnitude less than that of the larger scale drivers and highly dependent on the invasion stage (traits were associated only with native range drivers). This suggests that future research should explicitly link biological traits to the different stages of invasion, and that a failure to consider residence time or characteristics of the native range may seriously overestimate the role of biological traits, which, in turn, may result in spurious predictions of plant invasiveness.

Quaternary climatic oscillations profoundly impacted temperate biodiversity. For many diverse yet undersampled areas, however, the consequences of this impact are still poorly known. In Europe, particular uncertainty surrounds the role of Balkans, a major hotspot of European diversity, in postglacial recolonization of more northerly areas, and the Carpathians, a debatable candidate for a northern 'cryptic' glacial refugium. Using genome-wide SNPs and microsatellites, we examined how the interplay of historical processes and niche shifts structured genetic diversity of diploid Arabidopsis arenosa, a little-known member of the plant model genus that occupies a wide niche range from sea level to alpine peaks across eastern temperate Europe. While the northern Balkans hosted one isolated endemic lineage, most of the genetic diversity was concentrated further north in the Pannonian Basin and the Carpathians, where it likely survived the last glaciation in northern refugia. Finally, a distinct postglacial environment in northern Europe was colonized by populations of admixed origin from the two Carpathian lineages. Niche differentiation along altitude-related bioclimatic gradients was the main trend in the phylogeny of A. arenosa. The most prominent niche shifts, however, characterized genetically only slightly divergent populations that expanded into narrowly defined alpine and northern coastal postglacial environments. Our study highlights the role of eastern central European mountains not only as refugia for unique temperate diversity but also sources for postglacial expansion into novel high-altitude and high-latitude niches. Knowledge of distinct genetic substructure of diploid A. arenosa also opens new opportunities for follow-up studies of this emerging model of evolutionary biology.

Abstract. The literature suggests that small genomes promote invasion in plants, but little is known about the interaction of genome size with other traits or about the role of genome size during different phases of the invasion process. By intercontinental comparison of native and invasive populations of the common reed Phragmites australis, we revealed a distinct relationship between genome size and invasiveness at the intraspecific level. Monoploid genome size was the only significant variable that clearly separated the North American native plants from those of European origin. The mean Cx value (the amount of DNA in one chromosome set) for source European native populations was 0.490 AE 0.007 (mean AE SD), for North American invasive 0.506 AE 0.020, and for North American native 0.543 AE 0.021. Relative to native populations, the European populations that successfully invaded North America had a smaller genome that was associated with plant traits favoring invasiveness (long rhizomes, early emerging abundant shoots, resistance to aphid attack, and low C:N ratio). The knowledge that invasive populations within species can be identified based on genome size can be applied to screen potentially invasive populations of Phragmites in other parts of the world where they could grow in mixed stands with native plants, as well as to other plant species with intraspecific variation in invasion potential. Moreover, as small genomes are better equipped to respond to extreme environmental conditions such as drought, the mechanism reported here may represent an emerging driver for future invasions and range expansions.

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Detailed knowledge of the geographic distribution of cytotypes is a prerequisite for any experimental or molecular study of ploidy-variable plant systems. The Arabidopsis arenosa group, an intricate di-tetraploid complex from the plant model genus Arabidopsis, has remained largely neglected regarding the distribution and habitat associations of its cytotypes. Using flow cytometry, we conducted a large population-level cytological screen across the A. arenosa group range, involving more than 2900 individuals from 194 populations. We characterized a largely parapatric distribution of the diploid (Southeast Europe) and tetraploid (Northwest Europe) cytotypes with two contact zones -a narrow contact zone in the Slovenian Forealps and a diffuse contact zone across the Carpathians. In addition, a previously unknown isolated diploid lineage with distinct ecology was revealed from sandy areas of the southeastern Baltic coast. We also recorded several adult triploid individuals for the first time in wild Arabidopsis arenosa. Particularly in the Western Carpathians, the diploid and tetraploid populations are largely intermingled, and both cytotypes are spread along the whole lowland-alpine gradient of habitats, exhibiting no signs of ploidy-linked habitat differentiation. In contrast with the complexity at the landscape scale, the within-population cytological homogeneity and the rare occurrence of triploids indicate that the contact zone is rather stable.

Flow cytometry (FCM) is currently the most widely‐used method to establish nuclear DNA content in plants. Since simple, 1‐3‐parameter, flow cytometers, which are sufficient for most plant applications, are commercially available at a reasonable price, the number of laboratories equipped with these instruments, and consequently new FCM users, has greatly increased over the last decade. This paper meets an urgent need for comprehensive recommendations for best practices in FCM for different plant science applications. We discuss advantages and limitations of establishing plant ploidy, genome size, DNA base composition, cell cycle activity, and level of endoreduplication. Applications of such measurements in plant systematics, ecology, molecular biology research, reproduction biology, tissue cultures, plant breeding, and seed sciences are described. Advice is included on how to obtain accurate and reliable results, as well as how to manage troubleshooting that may occur during sample preparation, cytometric measurements, and data handling. Each section is followed by best practice recommendations; tips as to what specific information should be provided in FCM papers are also provided.

Background and Aims Polyploidy is an important driver of plant diversification and adaptation to novel environments. As a consequence of genome doubling, polyploids often exhibit greater colonizing ability or occupy a wider ecological niche than diploids. Although elevation has been traditionally considered as a key driver structuring ploidy variation, we do not know if environmental and phenotypic differentiation among ploidy cytotypes varies along an elevational gradient. Here, we tested for the consequences of genome duplication on genetic diversity, phenotypic variation and habitat preferences on closely related diploid and tetraploid populations that coexist along approx. 2300 m of varying elevation. Methods We sampled and phenotyped 45 natural diploid and tetraploid populations of Arabidopsis arenosa in one mountain range in Central Europe (Western Carpathians) and recorded abiotic and biotic variables at each collection site. We inferred genetic variation, population structure and demographic history in a sub-set of 29 populations genotyped for approx. 36 000 single nucleotide polymorphisms. Key Results We found minor effects of polyploidy on colonization of alpine stands and low genetic differentiation between the two cytotypes, mirroring recent divergence of the polyploids from the local diploid lineage and repeated reticulation events among the cytotypes. This pattern was corroborated by the absence of ecological niche differentiation between the two cytotypes and overall phenotypic similarity at a given elevation. Conclusions The case of A. arenosa contrasts with previous studies that frequently showed clear niche differentiation between cytotypes. Our work stresses the importance of considering genetic structure and past demographic processes when interpreting the patterns of ploidy distributions, especially in species that underwent recent polyploidization events.

Ranunculus section Batrachium (water crowfoot) ranks among the most taxonomically challenging aquatic plant groups due to morphological reduction, phenotypic plasticity, polyploidy and reticulate evolution. This study, for the first time in this group, linked morphology, genome size and genetic data (two non-coding regions of plastid DNA and the ITS region of nuclear ribosomal DNA). This extensive data set, including 258 central European populations, enables us to recognize widespread lineages from hybrids and to trace the evolutionary processes underlying the observed diversity. Most of the traditionally recognized species are supported. However, the presence of two morphologically cryptic but genetically well-differentiated lineages was detected within Ranunculus trichophyllus, and three separate lineages of different parentage were confirmed in the Ranunculus penicillatus complex. An allopolyploid origin was revealed in Ranunculus aquatilis, Ranunculus baudotii and in both lineages of R. trichophyllus, for which the parentage has not yet been studied, and allopolyploidy is suspected in all other polyploid taxa except for the triploid cytotype of Ranunculus fluitans, which is most likely autopolyploid. We detected putative F1 hybrids of seven different parentage combinations, including two involving Ranunculus rionii, representing the first known hybrids of this species. An additional 13 hybrid cytotypes (backcrosses or entailing additional polyploidization) were revealed; c. 20% of Ranunculus peltatus accessions seem to be influenced by introgression detectable only using sequence data. The Batrachium group is remarkable due to the coexistence of well-defined lineages with recently evolved biotypes arising due to hybridization and polyploidization.