Dramatic difference in rate of chromosome number evolution among sundew (Drosera L., Droseraceae) lineages.

This article focuses on the rates and patterns of chromosome number evolution in the carnivorous plant genus Drosera, particularly comparing the Australian subgenus Ergaleium with other subgenera. By critically reviewing chromosome count data and applying the BiChrom model within a phylogenetic framework, the study found that Drosera subg. Ergaleium exhibits significantly higher rates of single chromosome gain and loss—6-fold and 358-fold greater, respectively—than other subgenera, while rates of polyploidy did not differ significantly. Contrary to expectations, self-incompatible species, which are more common in D. subg. Ergaleium, showed higher rates of single chromosome loss than self-compatible species. The study found no evidence linking these rate differences to centromere type (holocentric versus monocentric) or post-polyploidy diploidization, suggesting other factors influence chromosome evolution in this group. These findings highlight the complexity of chromosome number changes as drivers of speciation and underscore the need for further cytological and molecular investigations into their evolutionary mechanisms.