Morphological studies of pollen grains of the Polish endemic species of the genus Rubus (Rosaceae)

The pollen of six taxa of the genus Rubus endemic to Poland (R. capitulatus, R. chaerophylloides, R. ostroviensis, R. posnaniensis, R. seebergensis and R. spribillei)was studied using light and scanning electron microscopy. The study objective was to extend the knowledge of the species pollen morphology and to investigate whether pollen morphology may help to taxonomically distinguish a very rare bramble species. Study material was derived from six natural localities where the species occur in the Wielkopolska region (Poland). Ten quantitative pollen grain features were analysed as well as the following qualitative ones: outline, shape, type of bridge and exine sculpture. Only mature, correctly formed pollen grains (30 per specimen) were measured and 180 pollen grains were examined in total. It was found that R. capitulatus and R. seebergensis had the highest mean values of P, E and Le features. In addition, pollen grains of R. capitulatus were most flattened (mean P/E ratio equals 1.14), while those of R. seebergensis were most elongated (mean P/E ratio equals 1.27). R. spribillei was the only species with striae of similar width as muri, whereas striae in the remaining species were wider. R. chaerophylloides and R. posnaniensis were characterised by specific, similar exine sculpture. Nevertheless, it should be stated that differences between pollen features of the species studied are so small and the variability of these features are so large that it is difficult to clearly identify the species studied. Therefore, pollen grain morphology can serve only as an auxiliary feature for the determination of these species.