Introduction: Trifolium is one of the important genus in Fabaceae family comprises 250 annual and perenial species in the world. Between annual species in Vesicaria SECT.on specially T. tomentosum, T.bullatum and T. clusii have similarity specially in flower and fruit morphology, so their distinction is difficult.Aim: Morphological study of pollen grain in these species were used for evaluating the Zohary classification in this SECT.on.Material and method: Specimen from Vesicaria SECT.on was gathered from different parts of Iran. By using SEM, P, E, PIE and furrow length, ornamentation of exine surface in equitorial and polar view, were specified for each species in 3 samples.Result: Pollen shape is oblong, and ornamentation of pollen surface is reticulate to rugose. The largest pollen grain belongs to T.fragiferum and the smallest one belongs to T.clusii. The characters such as ornamentation surface, P, E and furrow length were considered as the most important resource of variation by factor analysis. The species identification key were prepared accordingly.Conclusion: These results showed that pollen sculpture can separate T. tomentosun from T. bullatum that have similarity in morphology. Also, the most varieties characters such as P, E and exine sculpture, can identify other species.