Functional morphology, biomechanics and biomimetic potential of stem-branch connections in Dracaena reflexa and Freycinetia insignis.

Branching in plants is one of the most important assets for developing large arborescent growth forms with complex crowns. While the form and development of branching in gymnosperms and dicotyledonous trees is widely understood, very little is known about branching patterns and the structure of branch-stem-junctions in arborescent monocotyledons. For a better and quantitative understanding of the functional morphology of branch-stem-junctions in arborescent monocotyledons, we investigated the two species Dracaena reflexa and Freycinetia insignis. While D. reflexa is able to develop large arborescent forms with conspicuous crowns by anomalous secondary growth, F. insignis remains relatively small and is only capable of primary growth. Biomechanical investigations were performed by applying vertical loads up to rupture to lateral branches of both species. This allows the analysis of the fracture mechanics and the determination of the maximal force, stress and strain at rupture as well as the fracture toughness. Functional morphology was correlated with the mechanical behaviour of these plants and compared to data of other dicotyledonous trees. The high energy absorption found in the rupture process of lateral branches of D. reflexa and F. insignis makes them promising biological concept generators with a high potential for biomimetic implementation, i.e., for the development of branched fibre-reinforced technical composites. A wide range of constructional elements with branched (sub-)structures can be optimised by using solutions inspired by plant ramifications, e.g., in automotive and aerospace engineering, architecture, sports equipment and prosthetic manufacturing.