Abstract:

Pollen grains of 26 wild Rhododendron species in southwest mountain region of Sichuan were observed by using scanning electron microscope (SEM), among which 21 species were reported for the first time. They belonged to 3 subgenera (Subgen. Rhododendron, Subgen. Hymenanthes, Subgen.Pseudorhodorastrum), 4 sections and 12 subsections. All of them were tetrahedron with tetrad construction. Pollen grains of Rhododendron were spherical or subspherical with tricolporate and few of them with four colporates. There were varied visein threads on the surface. The size of tetrad and the pollen exine sculpture of them were different under SEM, whereas there was no conspicuous difference in the colpus and proximal exine. The difference of pollen exine sculptur and length and width of germinal apertures was not able to be used for classifying the subgenera, while the diameter of tetrahedron could be a trait used for further taxonomy. In the same subgenera, the morphology data of pollen could be used as supplementary characteristics to identify the section and subsection. It was not suitable for species indentification in Rhododendron only by morphological characteristics of pollen, however, it might be used for identification of some species within certain section and subsection.

Key words: Rhododendron, scanning electron microscope (SEM), pollen morphology, taxonomic significance