Comparative pollen morphology of the genus Rhaponticoides Vaill. (Asteraceae) in Türkiye: Implications for taxonomy and phylogeny

The main focus of this research is the palynological investigation of Rhaponticoides Vaill. species naturally occurring in Türkiye. Light microscopy and scanning electron microscopy (SEM) were employed to examine the pollen morphology of nine Rhaponticoides species in detail. Hierarchical cluster analysis (HCA) was also conducted to identify closely related species and distinguish the investigated taxa based on palynological traits. The study found that the pollen grains were tricolporate, isopolar, monad, and radially symmetric, with an oblate-spheroidal shape as indicated by the polar/equatorial (P/E) ratio. The pollen measurements derived from the P/E ratio ranged between 0.85 and 1, values associated with the Serratula type of the basal clade. SEM analysis revealed that the exine ornamentation was echinate-perforate. Key palynological criteria for discriminating Rhaponticoides species included the polar and equatorial axes, exine thickness, colpus length and width, and the lengths of spines and costae. This study advances our understanding of the relationships among Rhaponticoides taxa and offers valuable insights for future taxonomic research.