Successful plant invasions are hypothesised to be associated with close environmental matching or species poor communities. However, positive correlations between non-native abundance and native plant richness can also arise due to habitat heterogeneity (defined here as variation in abiotic and biotic conditions over space and time). We analysed survey and palaeoecological data for macrophytes in lakes covering a gradient of eutrophication and connectivity to partition the roles of environmental matching, macrophyte diversity and habitat heterogeneity in explaining abundance and invasibility of Elodea canadensis, a widely distributed non-native macrophyte in Europe. There was no association between invasibility and macrophyte species richness. Instead habitat heterogeneity variously enabled the coexistence of native macrophytes and E. canadensis in lake metacommunities over time. Invasion resistance was associated with high native macrophyte cover and unfavourable environmental conditions. We show how spatial and temporal scales can determine the relationship between habitat heterogeneity and invasibility in lake systems.

To determine potential drivers of the global distribution of ploidy in aquatic macrophyte species we allocated ploidy state to 1572 species occurring in 238 10 × 10° gridcells worldwide. Analysis of the relationship of 16 global-scale spatial, landscape, environmental, and biotic variables with ploidy state using Boosted Regression Trees revealed temperature variables and evapotranspiration as the strongest predictors. There were contrasting latitudinal patterns between haploid/diploid and polyploid species, while species richness measures also influenced ploidy state. Polyploid species occupied larger geographical ranges than haploid/diploid species. Mixed ploidy species showed the highest latitudinal range size and maximum latitude of species occurrence. Our findings suggest that increased chromosome number is associated with tolerance of a wider range of environmental conditions in macrophyte species. Mixed ploidy could reflect adaptability to expand geographical occurrence via chromosome number change, with such species predominantly occupying a latitude range intermediate between haploid/diploid and polyploid macrophyte dominance.