Although geneticists and archaeologists continue to make progress world-wide in documenting the time and place of the initial domestication of a growing number of plants and animals, far less is known regarding the critically important context of coalescence of various species into distinctive sets or complexes of domesticates in each of the world's 10 or more independent centers of agricultural origin. In this article, the initial emergence of a crop complex is described for one of the best-documented of these independent centers, eastern North America (ENA). Before 4000 B.P. there is no indication of a crop complex in ENA, only isolated evidence for single indigenous domesticate species. By 3800 B.P., however, at least 5 domesticated seed-bearing plants formed a coherent complex in the river valley corridors of ENA. Accelerator mass spectrometer radiocarbon dates and reanalysis of archaeobotanical assemblages from a short occupation of the Riverton Site in Illinois documents the contemporary cultivation at 3800 B.P. of domesticated bottle gourd (Lagenaria siceraria), marshelder (Iva annua var. macrocarpa), sunflower (Helianthus annuus var. macrocarpus), and 2 cultivated varieties of chenopod (Chenopodium berlandieri), as well as the possible cultivation of Cucurbita pepo squash and little barley (Hordeum pusillum). Rather than marking either an abrupt developmental break or a necessary response to population-packing or compressed resource catchments, the coalescence of an initial crop complex in ENA appears to reflect an integrated expansion and enhancement of preexisting hunting and gathering economies that took place within a context of stable long-term adaptation to resource-rich river valley settings.