Flow resistance in vegetated streams is generated by both the drag force exerted by plants and bed friction. Nevertheless, since surface friction is often neglected in the literature, drag is considered the preeminent resistance source. Flume tests were analysed in this study to assess the flow resistance component due to surface friction over a rough bed for different arrangements of artificial flexible plants that resemble plant species typical of vegetated floodplains and riparian areas. The plant drag was measured through drag force sensors and the bed friction factor was estimated by applying the linear superposition principle. It comes out that the contribution of the bed friction must be properly considered in the estimation of the total flow resistance, especially in low-density plant arrangements, where it reaches up to 25 %. Furthermore, the Leaf Area Index (
) can serve as an indicator for assessing the variability of bed shear stress across different leaf mass conditions. This study also indicates that
is a reliable predictor of plant density classification in vegetated beds, being a robust canopy biomass proxy, independent of the experimental hydrodynamic conditions, much more easily retrievable than the plant density parameter
, especially for flexible plants and in reach-scale studies. Specifically,
indicates sparse vegetation,
represent dense vegetation, and values in between correspond to transitional plant density. Finally, it is demonstrated that the classical logarithmic and power flow resistance formulae are not sufficiently accurate to predict bed friction for plant species typical of vegetated floodplains and riparian zones, leading to substantial underestimations (up to 95 %)
