Background and Aims: In several disciplines, identifying relevant root traits to characterize the root system architecture of species or genotypes is a crucial step. To address this question, we analysed the inter-specific variations of root architectural traits in two contrasting environments. Methods : We sampled 60 species in natura, at two sites, each presenting homogeneous soil conditions. We estimated for each species and site a set of five traits used for the modelling of the root system architecture: extreme tip diameters (Dmin and Dmax), relative diameter range (Drange), mean inter-branch distance (IBD) and dominance slope between the diameters of parent and lateral roots (DlDm). Key Results : The five traits presented a highly significant species effect, explaining between 77 and 98 % of the total variation. Dmin, Dmax and Drange were particularly determined by the species, while DlDm and IBD exhibited a higher percentage of environmental variations. These traits make it possible to confirm two main axes of variation: ‘fineness–density’ (defined by Dmin and IBD) and ‘dominance–heterorhizy’ (DlDm and Drange), that together accounted for 84 % of the variations observed. Conclusions : We confirmed the interest of these traits in the characterization of the root system architecture in ecology and genetics, and suggest using them to enrich the ‘root economic spectrum’.