Global macrophyte ploidy
Ploidy state information was collected for 1572 species, representing 45.0% of the known total global pool of vascular aquatic macrophyte species (ranging between 50.7 - 100% of the total number of species present per gridcell) (Appendix A2). The macrophyte ploidy database showed that 48.4% of the species are haploid/diploid (D), 34.6% polyploid (P), and 17.0% had mixed ploidy (D&P) (Fig. 1a). We observed that the incidence of percentage of P in macrophyte assemblages increased with increasing distance from the Equator, the percentage occurrence of D decreased at high latitudes, and D&P species showed an intermediate peak of occurrence around the 50° latitude band (Fig. 1b; Fig. 2; Appendix 3).
Overall, the Northern hemisphere has more available macrophyte ploidy information than is available in the literature for Southern hemisphere species, and species of non-tropical regions are much better represented than tropical species (Appendix A2). Two mainly tropical ecozones, Afrotropics (AFR) and Neotropics (NEO), had the lowest proportion of species with ploidy information available, reflecting the general lack of karyological effort involving low-latitude macrophyte species (for tropical endemics in particular). The other partly tropical ecozones, Orient (OR) and Australasia (AUS), are not as affected by this since they have a higher proportion of species from temperate areas. However, our findings indicated that there is generally little difference between ecozones in the percentage of occurrence of species from the three ploidy states. All six ecozones have between 40–50% D species present (with the highest value in NEO); between 30–40% for P species; and 20–30% for D&P species (except the NEO ecozone, which shows about 18% D&P species present).
Regarding endemic species, the observed global pattern across latitude bands was similar for both haploid/diploid and polyploid species, with significantly higher numbers of endemic species of both ploidy states in the tropics compared to those at the highest latitudes, >60°absolute (p<0.05). However, the actual mean numbers of polyploid endemic species per gridcell were only about half those for diploid species (reaching 10–11 polyploid species in the high latitude bands, compared to 18–19 haploid/diploid species in the same latitudes). A subsidiary peak was also seen for both endemic species ploidy states at 40–50°absolute, significantly higher than for the highest latitude bands but lower than values for the tropical latitudes. For mixed ploidy endemic species both the pattern and numbers were different from those seen for haploid/diplod and polyploid species. In this case there was a single peak of mixed ploidy species occurrence in the 40-60° latitude band, tailing away towards the Poles and also towards the Equator, while mean numbers of mixed ploidy endemic species per gridcell were also much lower, reaching no more than three – four species per gridcell in the peak latitude band.