Abstract: The pollen grains of five species and one variety of Calystegia from China were systemahcally examined under LM and SEM. The results arc as follows:Pollen grains are spheroidal, diam. about 53-108μ, pantoporate, with about 20-34pores. pores are circular, elliptical or irregular in shape, everyfive or four a group, arranged in a pantagon or a quadrilateral. Pore membrane is sunken or projecting, with about 5-20granules. The inteporal distance is about 7.8-18.2μ.Exine is 4-8μ thick, punctitectate, nexine is about 0.5μ thick, and sexine differs in thickness and tends to be thinner around pores. Minute supratectal processes, puncta and foveolae are present under SEM. Tectum is supported by bacula, Which are short, apically branched.The results indicate that Calystegia is a natural taxon. It perhaps originates from some pantocolpatc taxa of Convolvulus, or has a common ancester with them. Some channels between adjacent pores can be observed which may be an atavism or the pantoporatc pollen of Calystegia.In addition, there is a pollen specimen of C. dahurica (Beijing Botanic Gardens, 019) without tectum, and the branched bacula of the pollen grains are conspicuous. This type of pollen grains maybe results from an unknown mutation.

Key words: Calystegia, Pollen morphology, Taxonomic significance, China