With 29 species in Iran, Polygonum L. is comprised of annual and perennial plants in different habitats. P. aviculare makes a species complex, hardly distinguished from P. arenastrum and P. patulum. In the present study, po-llen grains, fruit surface and petals and leaves epidermis features were used to provide diagnostic features in order to se-parate species from one another. In Total, 33 populations of 6 annual species, including P. aviculare, P. arenastrum, P. patulum, P. argyrocoleon, P. polycnemoides and P. olivascens were studied. Specimens were gathered during field trips and studied by means of light and scanning electron microscopes. The Pollen grains of all the species which were stud-ied were monad, subprolate or prolate spheroidal and tricolpate. Main differences were also observed in their surface ornamentations. Length of equatorial and polar axes and colpus, granules diameters and the average distance between granules were other diagnostic features of the pollen grains. Statistical analysis of epidermis features revealed that the length and width of epidermis cells and stomata length varied in the species studied. A close relationship was found between P. aviculare and P. arenastrum on the one hand and P. argyrocoleon and P. olivascens on the other. The sepa-ration of P. polycnemoides could be attributed to differences in epidermis features. Results showed that a selected set of these features to be of taxonomic importance.