ytogeography of Caltha palustris (Ranunculaceae) from China

wenty-three C. palustris accessions and ten C. scaposa accessions have been cytologically investigated using the traditional chromosome tableting technique and flow cytometry (FCM), in order to investigate the evolution of C. palustris and C. scaposa in Caltha of Ranunculaceae. Caltha palustris was found to be a polyploid complex, which contained tetraploids (2n = 4x = 32), hexaploids (2n = 6x = 48), and octoploids (2n = 8x = 64), and C. scaposa were tetraploids (2n = 4x = 32) and octoploids (2n = 8x = 64). Tetraploids were common in C. palustris and C. scaposa; however, hardly any diploids were discovered. This finding may be explained by cytotype adaptive differences to the underlying heterogeneity of environmental factors. Most accessions of C. palustris and C. scaposa were from extreme habitats, such as the alpine mountains in the Qinghai–Tibetan Plateau. Ancestral diploids may have existed in this region during glacial periods and colonized most regions at the end of the glaciation cycles. However, individuals with other ploidy levels may gradually replace diploids, because of their increased fitness in changing environment. Moreover, there were two possible evolutionary colonization routes: one from Gan’su to Yunnan, and the other from Tibet to Yunnan. Molecular phylogeny have shown that C. scaposa is closely related to C. palustris, the chromosome size of C. scaposa was smaller than that of C. palustris, C. scaposa may be a relatively derived evolutionary taxon. More samples need to be analyzed in the future to better elucidate C. scaposa cytogeography because of only 10 accessions.