Crop genebanks keep a sample of the diversity in wild and cultivated germplasm. Knowing the structure of diversity within and among populations informs best decisions on efficient collecting, preservation and use. The US Potato Genebank has over 90 Solanum species, ranging in representation from only a few populations to several hundred. In a previous study we showed that populations of three species captured nearly all AFLP bands in polymorphic loci when represented by 100 populations that had been added over time to the genebank. In the current study we add analysis of two additional species and propose a simple metric, L100, to compare the expected marker diversity capture of 100 populations among different species. L100 detects when there is less population overlap and more rare markers, indicating that more populations are needed to capture the available diversity in a species.