Farmers of the Peruvian Andesmake use of seed-size variation as a source offlexibility in the production of ``nativecommercial'' farmer varieties of Andeanpotatoes and ulluco. In a case study of easternCuzco, the use of varied sizes of seed tubers isfound to underpin versatile farm strategiessuited to partial commercialization (combinedwith on-farm consumption and the next season'sseed). Use of seed-size variation also providesadaptation to diverse soil-moistureenvironments. The importance and widespread useof seed-size variation among farmers isdemonstrated in the emphasis and consistency oflinguistic expressions about (...) this trait. Smalland small-medium seed is typically sown in thecommunity's ``Hill'' unit of sub-humid,upper-elevation agriculture. Seed tubers ofmedium-size and larger are needed fordrought-stressed locales in lower-elevationlandscape units. Farm-level preferences for theseed-size of tubers also suggest potentialrelations to resource endowments of farmhouseholds and gender-related management,although these tendencies were notstatistically significant in the study. Anintra-varietal, landscape-environmentalperspective on seed-size management, whichincludes an emphasis on within-fieldversatility, helps to strengthen the researchsupport of local seed production in policiesand programs aiming for in situagrobiodiversity conservation, marketingcapacity, and food security. (shrink)