Conclusions
The total number of species recorded in our ploidy database is probably close to the total for which ploidy has so-far been assessed in macrophyte species. This ploidy database provides a useful resource to support further studies about the effects of varying environmental conditions on ploidy state in aquatic plants, at both regional and local scales, particularly in the context of scenarios of future climate change which suggest increased temperature and drought worldwide.
The findings of our study, utilising this database, improve knowledge of patterns of global distribution and diversity relating to ploidy state within a group of freshwater organisms, namely aquatic macrophytes, which both occur widely across the planet and are inherently adapted to a substantially-varied set of environmental stress conditions worldwide. The study also provides new information about drivers of ploidy at global-scale for this group of plants, including the use of plant assemblage diversity parameters to predict ploidy. In particular, our results provide evidence that climatic factors, especially temperature and evapotranspiration, play a strong role in driving distributions of macrophyte ploidy state, across the planet. Overall, our data strongly support the assertion that increased chromosome number may be an adaptation assisting vascular plant survival in a range of harsh environmental conditions, especially those typifying environmentally-stressed high latitudes.