Comparative pollen morphology of the genus Iberis L. (Brassicaceae) in Turkey and its taxonomic implications

In this study, we report the current palynological characteristics of Iberis taxa naturally distributed in Turkey. The pollen morphology of 10 native Iberis taxa was investigated across 35 populations. In the light of our taxonomic review of Turkish Iberis taxa, a detailed palynological description is provided for the genus. The palynological characteristics of Iberis taxa were examined using scanning electron microscopy (SEM) and light microscopy (LM) to confirm their diagnostic importance at a specific and/or generic level. We evaluated different characteristics including polar axis, equatorial axis, colpus length and width, amb diameter, apocolpium, exine structure, and sculpture. Pollen characteristics were measured on 30 pollen grains from each specimen under LM. Details of the exine sculpture were also analyzed under SEM. Generally, the pollen grains of the genus Iberis are small to medium sized, radially symmetrical, isopolar, spheroidal, almost tricolpate, and rarely syncolpate or tetracolpate. The exine sculpture is reticulate, and the structure is semitectate. Two pollen types for the genus were identified based on the colpus surface feature: Iberis type I (with non-ornamented colpus surface) and Iberis type II (with ornamented colpus surface). Principal component analysis and cluster analysis were performed to reveal patterns and groupings within the related taxa concerning pollen morphology. It was found that pollen size may provide a limited but valuable metric for distinguishing Iberis species. However, due to the wide variation in some populations, it would be useful to have palynological data alongside chromosomal, molecular and macro-micromorphological data to resolve the complexity in the taxonomy of the genus.