Plant biomass and seed production were quantified for Brassica tournefortii Gouan, Brassicaceae (Sahara mustard) from 3 sites spanning the Mojave and Sonoran deserts, in the Southwestern United States. We found strong linear relationships between plant biomass and seed production, with larger plants producing more seeds per plant (R² = 0.93) and greater seed biomass per plant (R² = 0.94). Both seed count (R² = 0.93) and seed biomass (R² = 0.90) were also greater in 0.25 m² plots that had higher plant biomass. These results and the law of constant final yield indicate that biomass and seed production of individual Sahara mustard plants can be higher in plots with lower densities. These data suggest that control efforts that do not remove all individuals may reduce densities but inadvertently increase net seed production within treated areas.