A plant leaf is generally composed of a petiole and a leaf blade. The petiole connects the leaf blade to the plant stem and, from a structural viewpoint, it resembles a cantilever beam. Petiole design is driven by the minimum use of material to withstand a combined torsion and bending load. The cross-section has a transverse size decreasing lengthwise and has a grooved shape. This paper examines the structural efficiency of the petiole shape. Ten petiole specimens of dicotyledonous plants have been investigated. Continuum mechanics and dimensionless factors are used to model the stiffness properties of the petioles. The results of the characterization are visualized on maps that contrast petiole efficiency to that of reference cross-sections. Nature shapes the petiole material to secure the best trade off between torsional compliance and flexural stiffness.