of eight wild species and varieties from Vigna subgenera Plectotropis and Vigna were screened for the non-protein amino acid p-aminophenylalanine (PAPA), previously reported to have a restricted taxonomic distribution and to be a growth inhibitor of Escherichia coli. The compound was detected in five wild species and its distribution found to have taxonomic value for assessing members of Plectotropis and intrageneric links with other taxa. Although quantitative variation in PAPA was detected between species and also between varieties of V. vexillata, toxicity tests confirmed that the levels detected in all accessions were sufficient for PAPA to be an important component of resistance against two important pest bruchids of Vigna and Phaseolus crops. The taxonomic and ecological significance of these findings is discussed.