LAUSR

AbstractThe size and shape of the pollen grains are studied in a hybridogeneous complex of the genus Onosma. This plant system encompasses the hybrid taxa O. helvetica and O. pseudoarenaria with bimodal karyotypes that comprise large and small chromosomes and their ancestral lineages, paternal O. fastigiata and Asterotricha taxa belonging to a maternal lineage. The pollen grains are investigated under light microscopy, and the size and shape parameters are retrieved based on image analysis of the pollen grain outlines. The shape of the pollen grain is analyzed by applying elliptic Fourier transform coupled with principal component analysis. Extensive size and shape variations of the pollen grain within cytotypes as well as differences between cytotypes are recorded. The cytotypes are mostly differentiated due to the size parameters of the pollen grain that are correlated with ploidy level and the proportion of large and small chromosomes. Despite significant differences being observed between cytotypes, the precise identification of the ploidy level of an individual based on the pollen size and shape analysis is not possible in most of the cases, mostly due to extensive intracytotype variation. Allometric analyses exhibit a different relation between the pollen shape and size in case of cytotypes. The ratio of polar to equatorial axes length is, generally, a good approximation of the pollen shape. However, the study clearly exhibits that the relation between pollen shape and the ratio of polar to equatorial axes length is different for cytotypes, which justifies the application of outline analysis in palynological studies.