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Polyploidization and Genome Size Evolution in Australian Billy Buttons (Craspedia, Asteraceae: Gnaphalieae)

Premise of research. The Australian members of the genus Craspedia (Asteraceae: Gnaphalieae) are known to contain polyploids, but only a very limited number of chromosome counts are available, and a systematic overview of ploidy levels and genome sizes is lacking. In the present study, we aimed to document chromosome number variation across the genus in Australia, test whether polyploids occur more often in alpine than in lowland environments, and test whether there is a proportional increase in genome size with polyploidy that would enable the use of flow cytometry as a proxy for chromosome counts in future studies. Methodology. We used flow cytometry to measure genome sizes (2C values) of 59 individual plants and obtained 45 chromosome counts from root tip squashes. Pivotal results. We found polyploidy to be common and documented intraspecific ploidy variation in several species, indicating multiple independent origins of polyploidy within the genus. Polyploidy was not more prevalent in high-elevation species than in lowland species. The highest ploidy levels cannot be differentiated on the basis of genome size. Conclusions. Occurrence in alpine habitats did not drive the evolution of polyploidy in Craspedia. Flow cytometry measurements of genome size cannot be used as a reliable proxy for the precise determination of higher ploidy levels across the genus. Patterns of genome evolution in Craspedia are complex, suggesting that detailed investigation will be necessary even for species-level studies or conservation management.