A comparative study on the petioles of four species of section Pedicellares in genus Rondeletia (Rubiaceae) was undertaken in order to investigate anatomical variations which may be useful in species identification. The cells of the cortical parenchyma are collenchymatously thickened in each species and contain antrachinon. The vascular tissue is horseshoe-shaped and open to the adaxial side. The abaxial side of the xylem is bordered by phloem. The species differ in presence or absence of trichomes, crystals, bundle size and number of lateral bundles.