Genetic diversity and differentiation of two narrowly endemic Origanum Species in Morocco: implications for conservation

Oregano is a highly valued aromatic and medicinal herb in the Mediterranean, appreciated for its culinary, therapeutic, and ecological significance. Classification within the Origanum genus is complicated by extensive morphological variation and frequent interspecies hybridization. In this study, we assessed the genetic diversity and population structure of O. elongatum and O. grosii across their full distribution in Morocco, sampling 264 individuals from seven populations and analyzing them with 13 microsatellite (SSR) markers. Despite its restricted native range, O. elongatum displayed considerable genetic diversity (Ho = 0.455, He = 0.429), whereas O. grosii showed lower diversity (Ho = 0.285) but higher differentiation among populations. Bayesian clustering, Principal Coordinates Analysis, and STRUCTURE analysis revealed four main genetic groups largely corresponding to geographic origin and clearly separating the two species. These results indicate strong species divergence and the existence of distinct population structures, underscoring the need for species-specific conservation measures. We recommend integrating in-situ and ex-situ strategies, including habitat protection, genetic reinforcement, and germplasm preservation in gene banks. Overall, this study illustrates how genetic data can inform conservation planning for rare endemic plants in ecologically sensitive regions, providing a model applicable to other Mediterranean mountain ecosystems facing climate and land-use pressures.