The seed-mediated growth of noble metal nanostructures with planar geometries requires the use of seeds lined with parallel stacking faults so as to provide a break in symmetry in an otherwise isotropic metal. Although such seeds are now routinely synthesized using colloidal pathways, equivalent pathways have not yet been reported for the fabrication of substrate-based seeds with the same internal defect structures. The challenge is not merely to form seeds with planar defects but to do so in a deterministic manner so as to have stacking faults that only run parallel to the substrate surface while still allowing for the lithographic processes needed to regulate the placement of seeds. Here, we demonstrate substrate-imposed epitaxy as a viable synthetic control able to induce planar defects in Au seeds while simultaneously dictating nanostructure in-plane alignment and crystallographic orientation. The seeds, which are formed in periodic arrays using nanoimprint lithography in combination with a vapor-phase assembly process, are subjected to a liquid-phase plasmon-mediated synthesis that uses light as an external stimuli to drive a reaction yielding periodic arrays of hexagonal Au nanoplates. These achievements not only represent the first of their kind demonstrations but also advance the possibility of integrating wafer-based technologies with a rich and exciting nanoplate colloidal chemistry.