Background: The genus Cyperus with six subgenera and 45 species is the second largest genus of the Cyperaceae family based on Flora Iranica. This genus includes 23 species in Iran, of which five are located in Northeast of the country. Aims: We determine the taxonomic boundaries among species of the genus Cyperus distributed in Northeast of Iran by using morphological and nut micro-morphological characters. Study Design: Morphometric and nut micro-morphology studies of species of Cyperus in northeast of Iran. Place and Duration of Study: Ferdowsi University of Mashhad Herbarium (FUMH), specimens collected during the growing season 2010 in Northeast of Iran (including three provinces of Khorassan Shomali, Khorassan Jonoubi, and Khorassan Razavi). Methodology: We numerically examined 43 morphological characters, nine morphological and nut micro-morphological traits on 80 herbarium specimens in order to determine the taxonomic value of the features and also to better discriminate Cyperus species distributed in Northeast of Iran. Results: The results revealed that morphological characters are somewhat useful to discriminate species of the genus in the region under study. Scatter plot displayed two distinct groups among samples. Individuals of C. longus are accommodated in the first group. Second group is divided into two subgroups. Individuals of Cyperus rotundus are located in first subgroup. Second subgroup is showed to be more complex by consisting of C. laevigatus subsp. distachyos, C. fuscus and C. glaber. The results obtained from stereomicroscope study indicated that nut of C. laevigatus subsp. distachyos is lenticular but nuts of other species are trigonous. The results of scanning electron microscope study revealed that C. laevigatus subsp. distachyos differentiated completely in terms of nut micro-morphology from the other species. Conclusion: The results confirm fully results obtained from previously anatomical study of these species. Also the scanning electron microscope study indicated that three species including C. rotundus, C. longus and C. glaber are similar in terms of nut micro-morphology.

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