Study of morphological diversity, antioxidant capacity, and essential oil compositions of <i>Mentha aquatica</i> L.

Abstract Water mint ( Mentha aquatica L.) is a medicinal plant with significant therapeutic potential for treating a wide range of diseases. Due to its ability to grow in various geological environments, this study aimed to determine the morphological and phytochemical variability of water mint populations in Northern Iran. Identical and equally sized rhizomes of ten water mint populations were collected from their natural habitats and then cultivated at an experimental farm site in Mazandaran province. The root and stem diameters of most populations were not significantly different. The leaf size varied between populations, with three (Marzonabad, Lafoor, and Hassanabad) exhibiting smaller leaves than the others. The populations with smaller leaf sizes demonstrated a higher leaf number. The highest antioxidant potential was observed in Hassanabad (40 m) and Kia‐kola (10 m), with the lowest IC50, while the maximum essentical oil (EO) percentage was found in Balamarznak (250 m). The gas chromatography and gas chromatography/mass spectrometry identified 30 components of EOs, and the main compounds were 1,8‐cineol (10.7–27.5%), menthofuran (1.4–17.7%), trans ‐caryophyllene (1.7–15%), germacrene D, and viridifloro (0–8.08%). Four chemotypes of water mint were distinguished based on biochemical features. Principal component analysis and heat map analysis revealed that leaf size and 1,8‐cineol exhibit the minimum variability. However, smart and sensitive morphological traits with the maximum variability were root weight, shoot weight, and the number of leaves and branches. In general, water mint populations with the highest antioxidant capacity and EO content can be obtained within the altitudinal gradient range of 250–300 m.