Chromosome classification and karyotype variation in Silene marizii and closely related species of section Elisanthe in the Iberian Peninsula

Dioecism is a rare phenomenon among angiosperms although dioecy evolved several times through independent events. There are few examples of plant families with the presence of heteromorphic sex chromosomes. Caryophyllaceae present dioecious species with heteromorphic sex chromosomes within the genus Silene. Here, we reported karyological data on the four closely related species of Silene section Elisanthe represented in the Iberian Peninsula, being the first time for S. marizii. We conducted several scatter plots between numeric variable pairs, a principal component analysis (PCA) and an UPGMA cluster analysis. The different karyotypes could be arranged in a series from the moderately asymmetrical to less asymmetrical. Based on their karyotypes, the species of the section Elisanthe could be classified into three groups: 1A, 2A and 2B. The karyotypes were simply insufficiently different to distinguish between species as showed the scatter plots, PCA and UPGMA dendrogram. Minimum differences in karyotype formula and asymmetry indices among the study species were observed and no significant differences were also obtained for sex chromosomes. Our results supported the recent origin of Silene sex chromosomes and, consequently, may be in the early stages of differentiation.