Title : The morphology of the structural elements of Rhododendron and their taxonomic significance
The flora of the Russian Far East is attractive by its biodiversity and the fact that there are boundaries of the distribution of East-Asian species. Among them are Rhododendron mucronulatum Turcz., Rh. dauricum ? Rh. sichotense. The specimens of the subsection Rhodorastrum are characterized by existence of convergent morphological traits, that, in turn, causes discussions concerning their taxonomic status. To discover questions related to taxonomy, leafs, pollens and seeds morphology were investigated, as well its correlation to different environmental factors. To do that, we applied methods of electronic scanning microscopy and geometric morphometry. The most significant features of pollens and seeds that are more steady and are not-related to climatic variables were obtained. The difference between species by their pollens is observed on the level of structural elements in the zone of apocolpium, mesocolpium and near the aperture space. For seeds the most significant taxonomical feature as a coefficient of elongation of the cell exotesta was pointed out. Population investigation of these features on the Primorsky krai territory showed the existence of areas where pollen grains and seeds combine structural elements of different species. The obtained results demonstrate existence of variability of structural elements, that is caused by climatic variables, as well likely processes of hybridizations, because the territory of Primorsky kray is a zone of sympatric distribution of Rh. mucronulatum, Rh. dauricum, Rh. sichotense.