Genome sizes and chromosomal repatterning in the evolution of Saxifraga and other Saxifragaceae

Abstract

The genus Saxifraga comprises ca. 480 species and is a characteristic element of mountainous and boreal to subpolar vegetation, particularly in the Northern Hemisphere. It comprises primarily perennial herbaceous plants that often form leaf rosettes and frequently have colorful, insect-pollinated flowers. This study used flow cytometry to estimate the genome sizes of saxifrage species on a broader taxonomic scale, identifying the total range of variation within the genus and its many infrageneric phylogenetic lineages. Measurements were made for 122 species, representing most of the infrageneric groups. Holoploid genome sizes (2C values) exhibited approximately 17-fold variation, whereas monoploid genome sizes (1Cx values) varied slightly less. The highest values were found in the predominantly Himalayan-Tibetan section Ciliatae, while the smallest were in the southern European subsection Arachnoideae. The genome size data were analyzed alongside karyological information, including chromosome numbers, polyploidy, changes in the chromosome base numbers (x = 8–14) and aneuploidy. The potential evolutionary patterns of chromosome and genome differentiation among the main lineages of Saxifraga were analyzed, and possible relationships of genome size with life form, morphology, habitat, ecology, and biogeography were outlined. Additional data were presented for five other Saxifragaceae genera. All the data were used together to evaluate the potential evolution of chromosome base number in Saxifraga and the entire family Saxifragaceae. Additionally, an updated infrageneric classification of Saxifraga was introduced, including the newly designated subsection Irriguae.