Leaf Morphometric Differentiation and Nearest-Road Proximity Among Three Natural Subpopulations of Rhododendron luteum in Lesvos, Greece

Rhododendron luteum has a single natural occurrence in Greece, restricted to western Lesvos, where understanding variation among its spatially separated subpopulations is important for conservation and forest-management planning. This study examined leaf morphometric differentiation among the natural subpopulations of Parakoila, Pterounta and Chidira and tested whether individual proximity to the mapped road network was associated with morphometric variation. A total of 900 leaves were collected from 90 plants (30 per subpopulation; 10 leaves per plant), and twelve leaf size-, shape- and proportion-related traits were quantified by digital image analysis. Inferential analyses were conducted at the plant level. Eight of the twelve traits showed significant subpopulation effects after false discovery rate correction. Multivariate analyses also supported overall differentiation (PERMANOVA: pseudo-F = 7.37, R2 = 0.145, p < 0.001), although substantial overlap among individuals remained. PCA indicated contrasting tendencies towards broader and rounder versus more elongated leaf forms, while leave-one-out discriminant analysis correctly classified 63.3% of plants. Nearest-road distance showed no consistent independent association with any morphometric trait after accounting for subpopulation and elevation, and this conclusion was robust across alternative model specifications. Overall, the three subpopulations showed significant morphometric differentiation, accompanied by substantial phenotypic overlap among individual plants, while the present data did not provide evidence of a consistent independent association with nearest-road proximity. Morphometric information may, therefore, complement genetic, ecological and spatial data in conservation-sensitive forest planning.