Aims The architecture of root systems determines where and how much resources plants can extract from the soil, how they compete for soil resources, and how they interact with soil organisms. We aimed to develop a 3D root-system model called RSCone for future inclusion into multispecies individual-based canopy models suitable to design integrated weed management or intercropping strategies. Methods We (1) proposed a conceptual root-system model consisting of empirical equations predicting root-system envelope, root length and biomass distribution from environmental conditions, species and plant stage, (2) calibrated the model from simulations with an existing architectural root-system model (ArchiSimple) to benefit from its knowledge on root functioning and the many parameterized crop and weed species, (3) identified the root-system architectural processes driving the key root state variables and (4) established species functional groups with Principal Component Analyses and clustering. Results RSCone consists of 17 equations and 14 parameters; it was calibrated for 22 weeds and 22 crop species and varieties. Six species functional groups were established, depending on their family (Poaceae, Fabaceae, other), root-extension rates, specific root length (SRL) and the time to reach maximum SRL. Conclusion RSCone is ready to be included into multispecies (crop and/or weed) dynamics models.