Article type: Advanced Review Article title: A Review of Plant-Flow Interactions on Salt Marshes: The Importance of Vegetation Structure and Plant Mechanical Characteristics Authors: Full name and affiliation; email address if corresponding author; any conflicts of interest James Alexander Tempest* Cambridge Coastal Research Unit, Department of Geography, University of Cambridge, Downing Place, Cambridge, CB2 3EN, Jat74@cam.ac.uk Iris Möller Cambridge Coastal Research Unit, Department of Geography, University of Cambridge, Downing Place, Cambridge, CB2 3EN Tom Spencer Cambridge Coastal Research Unit, Department of Geography, University of Cambridge, Downing Place, Cambridge, CB2 3EN The authors declare no conflicts of interest for this article. Abstract Observations of plant-flow interactions on salt marshes have revealed a highly complex process dominated by the tightly coupled effects of plant characteristics and hydrodynamic conditions. This paper highlights the importance of vegetation structures such as plant density and height, as well as their spatial variability and mechanical properties including flexibility, upon energy dissipation and flow modification. Many field, laboratory and modelling studies which attempt to predict flow dissipation or improve our understanding of plant-flow interactions use simplified structural measures of salt marsh vegetation or artificial representations. These simplifications neglect important plant and canopy elements and are unlikely to be truly representative of their natural counterparts. Such approaches limit our understanding of plant-flow interactions and potentially compromise the predictive accuracy and application of numerical flow models. It is important therefore that improved techniques to measure vegetation structure are adopted in order to better define the key relationships between measurable plant characteristics and drag-relevant plant properties.