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Plants are a vital part of the world's biological diversity and have great economic and cultural importance. Plant biodiversity balances ecosystems, protects watersheds, mitigates erosion, affects climate, and provides shelter for many animal species. This study aimed to determine plant diversity in relation to the soil properties of semi-arid rangelands along a gradient at the watershed scale in the Oued Chabro, Algeria. Plants and soil were sampled at 27 points distributed in three sampling sites (upstream, midstream, and downstream). The floristic data was analyzed using species richness estimators, life forms, spatial occurrence, and multiple factor analysis. Moreover, the effects of soil properties on the taxonomic structure of plant communities in the sampling sites were analyzed using Pearson correlations. The characterized flora included 42 plant species classified into 18 families, and Asteraceae (38.1%), Poaceae (14.3%), Brassicaceae (7.1%), Amaranthaceae (4.8%), and Chenopodiaceae (4.8%) were the most representative in terms of species. The species Atractylis delicatula was dominant (relative abundance = 81.5%). The upstream site was characterized by a high vegetation cover, high species abundances, and richness in plant families and genera. Significant correlations were observed in this area between the number of genera, number of families, number of species, family richness, Pielou evenness index, and Simpson's concentration index. The upstream site was characterized by chamaephytes and phanerophytes; 16 species were exclusively present in this section. Two species were found in the midstream site and one (Scolymus hispanicus) was found in downstream site. The upstream site was positively correlated with plant litter, the midstream with barren soil, and the downstream study area was negatively correlated with coarse-grained materials and vegetation cover. This study demonstrated that differences in life forms, richness, and diversity exist among the three sampling sites due to the soil differences and the positions along the watershed. [ABSTRACT FROM AUTHOR]