Urban agriculture, including urban homegardens, is vital for urban survival of many people in various cities around the world, including those in the Amazon region of Brazil. These spaces, through daily praxis, become important for incidental agrodiversity conservation as food plants are cultivated and their plant material circulated. Utilizing data from a year-long intensive qualitative study of 25 rural-urban migrant households, this article considers the diversity of plant material in urban homegardens in the Amazonian city of Santarém, Pará, Brazil. The purpose of the study was to understand the social systems that maintain cultivated plant diversity in homegardens. Our objectives in this article are twofold: a) to demonstrate that plant agrodiversity in homegardens persists in a setting which is located 'at the market'; and b) to document the ways in which flows of plant material help maintain this agrodiversity.