While central Mexico continues to be a cradle of agrobiodiversity, there have been major changes to the agricultural model since the 1960's, characterized by an overall decrease in crop diversity and a shift from low-input subsistence farming to high-input commercial farming (Sanderson 1986). In light of this trend, this study focuses on agrobiodiversity and the specific practices associated with seed selection, cultivation, and use of diverse crops in central Mexico. Most related efforts have been made at the scale of "farm" or "nation;" the dynamics of agrobiodiversity at the scale of landscape are less well-understood. This study examines crop diversity within a specific community in central Mexico. Both quantitative measures of crop diversity and qualitative ethnographic data are interpreted through the frameworks of ethnobotany, economic botany, agroecology and human ecology. The agro-system of this community appears to be a relatively stable and sustainable form of agricultural syncretism containing high levels of agrobiodiversity. Using this community as a case study, the functional roles and implications of crop diversity on a bioregion are examined. This contextual examination is conducted with an awareness of the biosecurity threats posed by genetic erosion and the potential benefits of in situ conservation.