Pollen morphology of selected taxa of Valeriana (Caprifoliaceae): taxonomic and evolutionary implications

Pollen morphology of 34 herbarium specimens belonging to 17 taxa of the genus Valeriana was studied using light and scanning electron microscopy. The aim of this research was to evaluate the taxonomical value of palynomorphological data for species-specific identification. Pollen grains are monads, radially symmetrical, isopolar, tricolpate, oblate to prolate (P/E = 0.69–1.59); medium- or large-sized (P = 26.60–66.50 µm; E = 23.94–57.19 µm). Colpi are long, medium-length or short, with acute, obtuse or rounded ends. Four types and eight subtypes of exine sculpture were recognised: type I—echinate-verrucate (5 spp.), type II—echinate-nanoechinate-verrucate (10), type III—echinate-microechinate-nanoechinate-verrucate (1), type IV—echinate-microechinate-nanoechinate (1). Additional characters of taxa of Valeriana diagnostic at species level for the purposes of taxonomy are: size of pollen and colpi, exine sculpture: presence/absence of verrucae, their form, size and form of echini/microechini/nanoechini, their number, pattern of tectum in areas between echini, exine thickness in mesocolpia and apocolpia. Our palynomorphological data support the results of molecular phylogenetic studies. The close phylogenetic relationships of the species V. montana, V. tripteris, V. supina and V. pyrenaica are also supported by their palynomorphological characters, such as exine sculpture (type I). Cluster analysis mainly supports the definition of pollen types and subtypes (based on qualitative data), since species are grouped as five separate branches. The pollen grains of five taxa were analysed for the first time in the current study.