Plant-based systems for nutrient sequestration into valuable biomass have the potential to help avoid the environmental problems associated with the disposal of large volumes of animal waste. The objective of this study was to select superior duckweed (Lemnaceae) genotypes for the utilization of nutrients in animal wastes. A two-step protocol was used to select promising duckweed geographic isolates to be grown on swine lagoon effluent. Forty-one geographic isolates from the worldwide germplasm collection were used in an in vitro screening test, because they were noted to be fast-growing genotypes during routine collection maintenance. In vitro screening was accomplished by growing geographic isolates on a synthetic medium that approximated swine lagoon effluent in terms of nutrient profile, total ionic strength, pH, and buffering capacity. Large differences among geographic isolates were observed for wet weight gain during the Ii-day growing period, percent dry weight, and percent protein in dry biomass. Total protein production per culture jar differed 28-fold between the most disparate of the 41 geographic isolates and was the variable used for selection of superior geographic isolates. The challenge of eight of the 41 geographic isolates with full-strength swine lagoon effluent in the greenhouse led to the selection of three that are promising as genotypes to be grown on lagoon effluent.