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.