As part of the PBI: Solanum grant I am using morphological and molecular markers to investigate species boundaries and relationships in the wild potato Solanum brevicaule complex. These represent about 30 morphologically very similar species that are hard to distinguish from each other and from the cultivated species. Van den Berg et al. (1998) studied the validity of species in the Solanum brevicaule complex using morphological data, and Miller and Spooner (1999) with nuclear RFLP data and RAPD data. All data were concordant in showing that 1) there were no species-specific morphological characters distinguishing species, and any species that may be valid would be distinguished only by use of a complex of widely overlapping traits (polythetic morphological support), 2) at best, two species were defined with a north-south geographical partitioning, one from Peru and northwestern Bolivia, and another from northwestern Bolivia to northern Argentina. In collaboration with Dr. Iris Peralta at the National University of Cuyo near Mendoza Argentina, I am studying these species in a replicated field trial of the same accessions of van den Berg et al. (1998) in Argentina. I am also exploring the use of molecular markers to refine knowledge of species boundaries and relationships.