Farmers’ knowledge of date palm (Phoenix dactylifera L.) agrobiodiversity in a Saharan oasis: Folk nomenclature, fruit morphometrics and varietal turnover over four decades at Taghit, south-western Algeria

Background Date palm ( Phoenix dactylifera L.) sustains oasis livelihoods through farming systems in which clonal propagation coexists with the retention of seed-derived palms. Documenting this diversity requires attention to how farmers name, distinguish and manage their palms. In south-western Algeria, long exposed to Bayoud disease, no inventory of the local varietal repertoire has been published for Taghit since 1985, to our knowledge. This study examined date palm diversity and farmers’ knowledge and practices in the Taghit oasis system, characterised fruit and seed variation among locally recognised varieties, and assessed changes in the repertoire over four decades. Methods Semi-structured interviews with 70 farmers across 39 palm groves in six localities documented varietal names, cultivation practices, knowledge transmission, uses and perceived constraints, including resistance to Bayoud. We analysed varietal frequency, salience and spatial distribution, and compared the repertoire with a 1985 inventory. Ten quantitative fruit and seed traits were measured on 600 fruits from 75 palms representing 30 varieties to assess variation within and among varieties. Results Farmers reported diverse uses of date palm products, regular grove management and continuing intergenerational knowledge transmission. They collectively listed 30 varieties, comprising a widely shared core and numerous less frequent ones, twelve of which were recorded in only one grove. Richness and composition differed among localities. Varietal lists excluded males and collective seedling categories, while ḫalṭ served both as a varietal name and as a collective designation for seed-derived palms. Fruit and seed traits clearly differentiated varieties, with variety accounting for 96.7% of the variance among palm means. After harmonisation, the 1985 and current inventories each comprised 30 varieties, but only fourteen were shared, and historically common varieties were more often recovered. Perceived Bayoud resistance may have contributed to changes in the repertoire, as illustrated by tākarbūš, introduced for its reputed resistance, still uncommon in 1985 but now established. Conclusions Our study highlights smallholders’ role in maintaining perennial crop diversity through clonal propagation, retention of seed-derived palms and local knowledge. Conservation should support the practices and knowledge transmission that sustain this diversity, household livelihoods and oasis landscapes.