Effects of phyllotaxy on biomechanical properties of stems of Cercis occidentalis (Fabaceae)

• Published in: American journal of botany 2014, Vol.101 (1), p.206-210
• Main Authors: Caringella, Marissa A, Bergman, Brett A, Stanfield, Ryan C, Ewers, Madeleine M, Bobich, Edward G, Ewers, Frank W
• Format: Article
• Language: English
• Subjects: animals; Bending; Biomechanical Phenomena; biomechanics; Biomimetics; Botany; BRIEF COMMUNICATION; Cercis; Cercis occidentalis; cracking; Elastic Modulus - physiology; energy; engineers; Fabaceae; Fabaceae - physiology; flexural stiffness; Flowers & plants; fruits; gravity; Internodes; leaf nodes; Leaves; mechanical properties; modulus of elasticity; Phyllotaxis; phyllotaxy; Pith; Plant Leaves - anatomy & histology; Plant Leaves - physiology; Plant Stems - anatomy & histology; Plant Stems - physiology; rain; shoots; snow; Stems; Stiffness; Timber; Tissues; Vascular plants; wind; wood density; woody plants; Xylem; Xylem - physiology; Young's modulus
• ISSN: 0002-9122; 1537-2197
• DOI: 10.3732/ajb.1300260

• Premise of the study: Phyllotaxy, the arrangement of leaves on a stem, may impact the mechanical properties of woody stems several years after the leaves have been shed. We explored mechanical properties of a plant with alternate distichous phyllotaxy, with a row of leaves produced on each side of the stem, to determine whether the nodes behave as spring-like joints.• Methods: Flexural stiffness of 1 cm diameter woody stems was measured in four directions with an Instron mechanical testing system; the xylem of the stems was then cut into node (former leaf junction) and nonnode segments for measurement of xylem density.• Key results: Stems had 20% greater flexural stiffness in the plane perpendicular to the original leaf placement than in the parallel plane. The xylem in the node region was more flexible, but it had significantly greater tissue density than adjacent regions, contradicting the usual correlation between wood density and stiffness.• Conclusions: Nodes can behave as spring-like joints in woody plants. For plagiotropic shoots, distichous phyllotaxy results in stems that resist up-and-down bending more than lateral back-and-forth movement. Thus, they may more effectively absorb applied loads from fruits, animals, wind, rain, and snow and resist stresses due to gravity without cracking and breaking. Under windy conditions, nodes may improve damping by absorbing vibrational energy and thus reducing oscillation damage. The effect of plant nodes also has biomimetic design implications for architects and material engineers.