Taxonomic significance of pollen morphology of Pterocephalus plumosus (Caprifoliaceae)

Comparative palynological studies of Dipsacaceae s.str. show considerable diversity in the pollen grain morphology of its representatives. The aim of this research was to provide more detailed palynomorphological data on selected taxa whose pollen grains are characterised by tricolpate apertures (Pterocephalus plumosus, Succisa pratensis and Succisella inflexa). The pollen morphology of P. plumosus was studied using both light microscopy and scanning electron microscopy. The pollen grains are tricolpate, suboblate to prolate; large in size. Their outline in polar view (amb) is subcircular, rarely trilobate. The brevicolpi have a distinct margo and acute ends. The exine sculpture is echinate-microechinate-nanoechinate. The exine structure (columellae) of the pollen grains of P. plumosus, S. pratensis and S. inflexa was analysed for the first time in the current study. Pollen grains in P. plumosus are distinguished by long and dense columellae in the mesocolpia, and longer in the apocolpia. Our new ?alynomorphological data support a close relationship between S. pratensis and S. inflexa by the presence of shorter sparse columellae throughout the pollen exine. The UPGMA dendrogram shows the distinctive morphometric characters of P. plumosus pollen grains, which is thus included as a separate branch.