Abstract: To elucidate taxonomic relationships among the families of Pentapylacaceae,Sladeniaceae and Theaceae,pollen grains of genera,ca.20 species representing three families stated above were examined by light,scanning electron,and transmission electron microscopes.The comparison of pollen morphology shows that the pollen grains of Sladeniaceae are very similar to those.Their pollen grains are oblate to nearly spheroidal and 3- solporate,from rugulate to rugulate -reticulate sculptures and exine structure consisting of thick tectum and columellae,and thin endexine. Howere,the pollen grains of Pentapylacaceae are different relatively from those of Theaceae for having nearly psilate pollen surface and exine structure consising of thin recum,undeveloed columellae and thick endexine though the pollen shape (oblate) and aperture (3-colporate ) are similar to those of Theaceae.As far as the pollen sculpture and exine structure are concerned ,Pentaphylacaceae is more similar to Clematoclethra Maxim. of Actinidiaceae than of Theaceae.

Key words: Pollen exine ultrastructure, Pentapylacaceae, Sladeniaceae, Theaceae.