By contrast, the petioles of large pinnate leaves, as well as stems, typically resist torsion by placing stiff materials with high elastic moduli (like sclerenchyma) toward the perimeters of their cross sections.
An example of this is leaf petioles. Some species of trees have pinnate leaves which, when the leaves fall, shed pinnae from the petiole, which is then left as a tapering, somewhat flexible rod.
The presence of a petiole (narrow body segment) is the defining characteristic distinguishing the suborder Apocrita (ants, bees and wasps) from the rest of order Hymenoptera (i.e., from the paraphyletic suborder Symphyta).