In the twentieth century, plant explorers in many countries were enlisted in the assembly of seed and plant collections that brought together hundreds and sometimes thousands of varieties of the same crop species. These collections were, and are, understood chiefly as the foundations for effective plant breeding. Crop seed collections, like other biological collections, were also essential tools of taxonomy; their study was both conditioned by and productive of evolutionary narratives about plant cultures and human natures. A search for Zea mays (maize or corn) and its wild relatives in South America in the 1940s revealed that developing taxonomies of cultivated plant species, especially accounting for distinct local forms of these crop plants, was a profoundly interdisciplinary enterprise. It was also a project conditioned by researchers’ expectations of the places, peoples, and plants that they would encounter. The taxonomy of maize, like other taxonomic enterprises, emerged as a mirror of those who taxonomized.