Abstract
<title>Abstract</title> <p> The mastic tree, <italic>Pistacia lentiscus</italic> L. (Anacardiaceae), is an important Mediterranean shrub whose Moroccan populations had never been characterised in an integrated way. This article brings together three complementary studies carried out on the same eleven natural populations, sampled along a Middle Atlas–High Atlas–Souss bioclimatic gradient, and reads them as a single body of evidence. Morphological analysis of 24 traits revealed large variation among and within populations. Inter-simple sequence repeat (ISSR) markers showed high genetic diversity—about 91% polymorphic loci, a mean polymorphism information content of 0.79 and a total gene diversity of 0.31—together with strong differentiation (fixation index F <sub>ST</sub> = 0.42; gene flow Nm ≈ 0.95) and five gene pools; a hierarchical analysis of molecular variance (AMOVA) showed that geographic and bioclimatic groupings together explained under 4% of the molecular variation. Macro-biochemical analysis of the leaves found significant differences among populations in minerals, nitrogenous matter, protein and energy value, and resolved four groups. Mantel and partial Mantel tests further showed that the three levels are statistically independent of one another, and that genetic and biochemical differentiation is unrelated to either geographic or bioclimatic distance; only morphology tracked the environment, an isolation-by-environment pattern consistent with phenotypic plasticity. Diversity is thus high at every level and, for neutral and biochemical markers, decoupled from geography and climate. These results point to dioecy, outcrossing and bird-mediated dispersal as the main drivers. They argue for conserving a network of populations, not a few sites, prioritising the arid-margin Souss stand under a drying climate. </p>