Diploids and polyploids in the Santolina chamaecyparissus complex (Asteraceae) show different karyotype asymmetry

A traditional karyomorphological approach was carried out in order to investigate the cytotaxonomic relationships among the species of the Santolina chamaecyparissus complex. All the 14 species included in this species complex were analysed for a total of 39 populations. Metaphase plates were obtained by squashing root tips stained with Feulgen technique. Measurable metaphase plates available in literature were also re-analysed. Chromosome number (2n), total haploid (monoploid) length (THL), and karyotype asymmetry indices (CVCL and M-CA) were calculated for each of the 14 species. Chromosome data are provided for the first time for S. benthamiana and S. vedranensis, while a new hexaploid cytotype is reported for S. villosa. Five different ploidy levels are detected: diploid, triploid (a single individual of the otherwise diploid S. virens), tetraploid, pentaploid, and hexaploid. Our analyses reveal that polyploids are characterized by a more asymmetric karyotype with respect to diploids. The possible origin of polyploids, and in particular of the cultivated pentaploid S. chamaecyparissus, is briefly discussed.

Automated summary

In this study, a traditional karyomorphological approach was used to investigate the cytotaxonomic relationships among the species of the Santolina chamaecyparissus complex. Chromosome number, total haploid length, and karyotype asymmetry indices were calculated for each species. The results showed that polyploids have a more asymmetric karyotype compared to diploids. Chromosome data were provided for S. benthamiana and S. vedranensis for the first time, and a new hexaploid cytotype was reported for S. villosa.