<p>African locust bean (<i>Parkia biglobosa</i>) is an agroforestry tree species of major socio-economic importance in West Africa. Although several studies have reported strong morphological variability along environmental gradients, the influence of size class on the assessment of this variability remains insufficiently documented in the different agroforestry systems. This study analyzed intra- and inter-population morphological variation in <i>P. biglobosa</i> while explicitly integrating size class as a structuring factor. A total of 350 trees from three geographically distinct populations were sampled and categorized into to three size classes corresponding to ontogenetic stages (young, adult, and old). Thirteen dendrometric and foliar descriptors were recorded for each individual. Variability patterns were assessed using dispersion metrics, comparative statistics and multivariate analyses to characterize intra-population variation, inter-population differences, and the structuring of morphological diversity at each size class. Dendrometric traits exhibited high intra-population variability, whereas foliar traits were comparatively more conserved. Within-population variability was strongly influenced by size class. At each size class, population differences were explained by distinct combinations of dendrometric and foliar traits, with the identity of discriminant traits varying with size class. Morphological classification revealed structuring patterns that were independent of geographical provenance and showed a progressive increase in the number of discriminant variables with tree age. Overall, the findings demonstrate that morphological comparisons among <i>P. biglobosa</i> populations are strongly dependent on the size class of the individuals analyzed. They underscore the need to incorporate ontogenetic control in studies of morphological diversity and provide valuable guidance for conservation planning, phenotypic selection and the sustainable management of agroforestry stands.</p>