A sample of Solanum stoloniferum Schltdl. (reclassified from Solanum fendleri A. Gray), PI 620874, was collected by the authors from a previously undocumented site in the Patagonia Mountains of southern Arizona in September 2001. When original seed was grown at the US Potato Genebank, two of 25 seedlings produced white flowers. Upon closer inspection they were found to be completely without purple pigmentation on the tubers, stems, and underside of leaves-a characteristic previously unknown in this species and rare in wild potato overall. Solanum stoloniferum, like other species of series Longipedicellata (LON), is a disomic tetraploid. Results of crossing trials were consistent with the most simple genetic explanation for this phenotype: a recessive p allele at the P locus, making the mutant (pp pp), or "Purple-less" abbreviated "P-less." P-less plants were testcrossed with nearly 200 other LON populations originating across the U.S.A. and Mexico to make BC1 generations that had either one-half or one-quarter P-less seedlings. Surprisingly, about one-third of the populations, and from widely distributed origins, produced one-half P-less progeny, indicating that they also possess the recessive allele on one genome. Since this mutant has not been confirmed as an allele at the original P locus, its designation with the same allele symbols in this report (P and p) is provisional. This discovery of the widespread p allele in LON and P-less mutants could provide a simple, unambiguous seedling marker for study of gene flow and dispersion, pollinator behavior in the wild, gene expression interactions between homeologous genomes, and chromosome pairing control.