Despite the role of polyploidy in multiple evolutionary processes, its impact on plant diversification remains controversial. An increased polyploid frequency may facilitate speciation through shifts in ecology, morphology, or both. Here we used Allium to evaluate (1) the relationship between intraspecific polyploid frequency and species diversification rate and (2) whether this process is associated with habitat and/or trait shifts.

Using eight plastid and nuclear ribosomal markers, we built a phylogeny of 448 Allium species, representing 46% of the total. We quantified intraspecific ploidy diversity, heterogeneity in diversification rates, and their relationship along the phylogeny using trait‐dependent diversification models. Finally, we evaluated the association between polyploidization and habitat or trait shifts.

We detected high ploidy diversity in Allium and a polyploidy‐related diversification rate shift with a probability of 95% in East Asia. Allium lineages with high polyploid frequencies had higher species diversification rates than those of diploids or lineages with lower polyploid frequencies. Shifts in speciation rates were strongly correlated with habitat shifts linked to particular soil conditions; 81.7% of edaphic variation could be explained by polyploidization.