Models of the energy and mass exchange between vegetation canopies and the atmosphere usually include formulations of the bulk boundary layer resistance of canopies (Rb) to describe the effects of the molecular diffusion at the leaf scale. Present formulations of Rb are either empircal expressions or are physically based models that are derived from a K-theory approach. However, K-theory has many known flaws and empirical expressions usually lump both canopy and soil effects into a single surface resistance. For areas of partial canopy cover, single surface (or single source) formulations of Rb have been difficult to formulate with any certainty and have proven difficult to validate. This study uses the 'localized near-field' Lagrangian model to derive Rb for the canopy component of a vegetated surface. Results show that foliage density (leaf area index), foliage distribution (one-dimensional leaf area density), and wind speed and leaf size can strongly effect Rb. For a large range of parameters the results can be approximated by a simple analytical expression. A sensitivity analysis (for heat transfer) suggests, assuming all other things remain the same, that vertical variations of the temperature difference between the foliage and the near-leaf canopy air space is important for estimating Rb, particularly for surfaces of partial canopy cover. Including possible soil flux into the model also suggests that single source estimates of Rb are extremely sensitive to the partitioning between soil and foliage contributions to the total heat flux.