Mango (Mangifera indica) is widely cultivated in Madagascar, particularly in the northwestern region, where diverse landraces have evolved outside formal orchard systems. However, few studies have examined how local people classify mangoes and describe their fruit traits. This study integrates ethnobotanical interviews and fruit trait analyses to explore vernacular naming systems and varietal differentiation in northwestern Madagascar. Interviews with 230 residents yielded 114 vernacular names and identified 39 distinct landraces based on fruit morphology. Local people recognized three major groups that closely paralleled morphological classifications: international commercial varieties (ICVs) with large reddish fruits; Malagasy seed-propagated landraces (GASY) with small green fruits; and the mangoes named Diego, Hiesy, and Zanzibar (DHZ) exhibiting intermediate fruit characteristics between ICV and GASY. While many studies warn that the introduction of improved cultivars can undermine the persistence of landraces, in Madagascar the grafted ICVs remain limited in extent and pose no immediate threat to local diversity. DHZ mangoes, maintained through polyembryonic seeds that stabilize fruit traits under extensive management, play a central role in household consumption and market sales. Although less commercialized, GASY landraces display high morphological variation and serve as important genetic reservoirs. These findings highlight how vernacular naming reflects local perceptual and cultural understandings of fruit tree diversity, and elucidate how morphological and naming variations together shape the landscape of mango diversity in Madagascar.