Bending properties of a macroalga: Adaptation of Peirce's cantilever test for in situ measurements of Laminaria digitata (Laminariaceae)

• Premise of the study: The mechanical properties of a plant are key variables governing the interaction between the plant and its environment. Thus, measuring variables such as the flexural rigidity (bending) of a plant element is necessary to understand and predict the plant–flow interaction. However, plant elements such as macrophyte blades can be relatively thin and flexible, thus difficult to characterize. Different adaptations of the classical 3‐point bending tests can also affect the interpretation of the flexural rigidity of an element. A simple, robust, method is newly applied to a biomaterial and validated here as an alternative to measure flexural rigidity of thin, flexible plant elements. • Methods: Based on a bending test procedure developed for the textile industry, an apparatus for in‐situ measurements was developed and compared with other normalized methods, then used in a field test on the blade of a marine macroalga ( Laminaria digitata ) to assess its suitability to measure the bending modulus of a biomaterial. • Key results: Results of the presented method on selected surrogate materials agree with a normalized cantilever method (ISO 9073‐7:1998) and 3‐point bending test (ISO 178:2010). Values determined for the bending moduli for blades of L. digitaria were in the typical range for algal material. The range of validity of the method is discussed. • Conclusion: By validating this method with existing norms, this study suggests a better approach to measure bending properties of different biomaterials in the field compared with more traditional bending tests and opens new possibilities.