We evaluated the leaf blade anatomical characteristics of thirty-three populations representing of 21 Nepeta L. taxa belonging to five sections from Iran to determine their taxonomic value in taxa delimitation and infrageneric classification in sections. Leaf samples of six individuals were examined per each population. The samples were fixed in F.A.A solution. The hand transverse sections were studied using light microscope, and data were analyzed using SPSS and MVSP softwares. We found that several leaf anatomical characteristics were common among the taxa and their populations; therefore, they had no taxonomic value. Hence, other anatomical features (the indumentum type, palisade cell wall shape, palisade/sponge cells ratio, parenchyma cells shape in midrib, the shape of vascular tissue, thickness of phloem and xylem tissues) differed among the populations and had the taxonomical importance. Moreover, the quantitative anatomical traits significantly (P B 0.001) varied among the taxa and their populations. The classification pattern of the studied taxa and their populations in UPGMA tree and PCA plot was inconsistent with the infrageneric classifications of the genus according to Flora of Iran and Flora Iranica. In addition, populations of some species were clustered separately. Since there was a high level of infraspecific diversity in Nepeta taxa, this issue should be considered in all taxonomical treatments of this genus to define the correct infrageneric classification pattern.
