This study investigated the relationships between root structure and anatomy and whole-plant functioning in herbaceous species. Fourteen annual and perennial species representative of a Mediterranean old-field succession were grown in monocultures in a common-garden experiment. Whole-plant functioning was assessed by inherent relative growth rate (RGR max), measured in standardized conditions, and maximum height ( Hmax). Root tissue density (TMD r), considered as a major component of root structure, was measured on roots harvested within in-growth cores. Anatomical characteristics were analysed on cross-sectional areas (CSA). TMD r was correlated positively with Hmax and negatively with RGR max. Root CSA explained interspecific variation in Hmax but not that in TMD r and RGR max. Root xylem CSA and xylem proportion in root CSA were positively correlated with TMD r and Hmax and negatively with RGR max. Mean xylem vessel CSA did not account for variations in TMD r , Hmax and RGR max. These results suggested that RGR max and Hmax are constrained by opposite root structural and anatomical traits, which have potential links with hydraulic conductance, support and longevity.