Phytochemical and palynological study of several species of Mentha L. in north of Iran

The genus Mentha L. is one of the most important taxa of the Lamiaceae family which is widely used in the food and pharmaceutical industries. Because of wide variety in morphological characteristics and frequent hybridization, the taxonomic classification of this genus is complex. Phytochemical and palynological studies, along with morphological characteristics, can be helpful in plant systematic and taxonomy. In this study, plant metabolites of various populations of M. aquatica, M. pulegium and M. longifolia species in Gilan, Mazandaran and Golestan provinces, by gas chromatography-mass spectrometry and spectrophotometeric methods, as well as their pollen morphology with scanning electron microscope were studied. The results showed that β-caryophylline and germacrene-D in M. aquatica, pulegone and menthone in M. pulegium and D-carvon and piperitenone oxide in M. Longifolia were the major chemical compounds in the essential oil. Moreover, the total amount of phenols, flavonoids, flavonols, saponins, carotenoids and chlorophyll a and b were significantly different among species and M. aquatica showed the highest amount of these secondary metabolites. The pollen grains in different populations of these species were monad, hexacolpate and often prolate-spheroidal with reticulate tectum surface. The polar length (P), equatorial width (E), P to E ratio, colpus width and the distance between two colpi in the pollen grains of these species showed significant differences; M. aquatica and M. pulegium species had the highest and lowest values. The results suggest that the secondary metabolites and the morphology of pollen grains can be effective in identification and taxonomic classification of these species.