Evaluation of Morphological Traits and Essential Oil Diversity in Different Populations of Hymenocrater oxyodontus Rech.f.

The study of medicinal plants in pasture ecosystems, alongside their ecological requirements, forms the foundation for developing valuable natural models for research and practical applications. Ecological factors primarily influence the type and quantity of essential compounds in medicinal plants. Economic utilization of these plants is feasible only when their compound levels are optimal. Therefore, understanding the factors that enhance active substances in medicinal plants is crucial. This study investigates the correlation between climatic, topographical, and edaphic parameters on the morphological traits and essential oil compounds in Hymenocrater oxyodontus Rech.f.

Three habitats of H. oxyodontus in Semnan province were selected, each with distinct environmental conditions. Within each habitat, 15 plots of 16 m² were established using a systematic random method. Morphological characteristics such as plant height, canopy diameter, canopy cover, biomass, and leaf area were measured. Flowering branches were collected in triplicate, and essential oils were extracted via hydrodistillation using a Clevenger apparatus. Essential oil compounds were identified by GC-FID and GC/MS. Soil samples from each habitat were analyzed for physicochemical parameters including pH, EC, OM, N, P, K, SP, lime, and texture. Variance analysis and data mean comparisons were conducted using SPSS software, with correlation analysis and PCA performed in Minitab software. The conservation status of H. oxyodontus was determined using the IUCN criteria via GeoCAT software.

Variance analysis of morphological traits revealed significant differences among the three regions for leaf area (0.1% level), plant height (1% level), canopy diameter, canopy cover, and biomass (5% level). Peygambar Mountain exhibited the highest values for plant height (35.4 cm), canopy diameter (69.2 cm), canopy cover (9.4%), leaf area (2.3 cm²), and biomass (135.1 g). Analysis of essential oil components also showed significant differences among regions at various levels (0.1%, 1%, and 5%). Dominant compounds in Peygambar Mountain included Trans-Cadina-1(6),4-diene (12.1%), Spathulenol (11.2%), Caryophyllene oxide (7.1%), and Nootkatin (7.1%). In Abar Mountain, Spathulenol (10%), α-Vetivone (6.8%), Caryophyllene oxide (6.1%), and Nootkatin (5.8%) were predominant, while 1,8-Cineole (16.4%), Hexadecanoic acid (8.9%), and Spathulenol (7.3%) were main compounds in the Parvar region. Soil physicochemical parameters showed significant differences in EC, OM, P, K, SP, lime, sand, and silt at the 0.1% level, pH and N at the 1% level, and clay at the 5% level. Peygambar region had the highest values for EC (1.3 ds/m), P (16.6 mg/L), OM (2.5%), N (0.14%), and sand (72%). Parvar region exhibited higher values for K (307.6 mg/L), lime (17.1%), SP (31.7%), silt (34%), and clay (12%). Significant correlations were found between altitude, annual precipitation, annual temperature, maximum temperature of the hottest month, OM, N, P, K, SP, lime, and both morphological traits and essential oil compounds. H. oxyodontus was determined to be CR (Critically Endangered) based on an AOO of 4 km² and an EOO of 15,735 km².

Environmental factors, particularly altitude, significantly affect the functional characteristics of H. oxyodontus. Vegetation indices were higher in the lower altitude Peygambar Mountain. For economic utilization, low-altitude areas are recommended for cultivation, whereas for therapeutic purposes, high-altitude areas like Parvar with higher concentrations of oxygenated terpenes are preferable. For commercial cultivation, mountain ecotypes' seeds are suggested.