Occurrence of tetraploid and hexaploid cytotypes between and within populations in Dianthus sect. Plumaria (Caryophyllaceae)

Summary The occurrence of both tetraploid and hexaploid cytotypes within and between populations of several species of Dianthus section Plumaria was analysed. Chromosome numbers for 13 populations of eight taxa are presented together with a thorough compilation of previously published data. Most of the taxa are polyploids (tetraploids and hexaploids). Three groups can be distinguished: (1) only one ploidy level within a taxon; (2) more than one ploidy level, but only single cytotypes within a population; and (3) populations with a cytotype mixture. From some populations, reported earlier to contain tetraploids, we found only hexaploid individuals. Hexaploids occur over the whole range of polyploid taxa, revealing no geographical pattern. Polyploidy is very likely the result of autopolyploidization, at least for the hexaploid cytotypes, which formed many times independently and occur sympatrically with tetraploids. Most of the populations with mixed cytotypes represent primary hybrid zones. It is not yet possible to decide whether directional (one cytotype will become extinct in the longer term) or balanced selection (both cytotypes can coexist) is acting in those populations.