South AmericanChenopodium assignable to sect.Chenopodium subsect.Cellulata (Chenopodiaceae) have been classified on the basis of fruit and leaf blade morphology. Samples representing 99 free-living and domesticated populations were included in a comparative study based on electrophoretic and morphometric data. The resulting patterns of variation indicate that past reliance on the fruit for diagnostic characters has obscured biological relationships. Domesticated and free-living populations of the high Andes, distributed from northwestern Argentina to Colombia, are closely allied and clearly separate from domesticated populations of coastal Chile and free-living populations of Argentina. Circumscription of the ArgentineC. hircinum to include Andean populations is rejected. Specific differentiation among Andean populations, polyphyletic origins forC. quinoa, and the presence of different ploidy levels are not indicated. Free-living Andean types sympatric withC. quinoa are provisionally placed within that species as subsp. milleanum. While the coastal quingua domesticate is clearly distinct from the Andean weed/crop complex, it is provisionally placed within subsp.quinoa to conserve established nomenclature. The overall pattern of morphogenetic variation among South American populations suggests a co-evolutionary relationship between domesticated and free-living populations of the high Andes, with a center of diversity at the southern extreme of the Andean range. Populations ofC. hircinum represent a logical link to the progenitor of the quinua complex, although firm phyletic and systematic alignments will require more information concerning populations of south-central Chile, and further definition of relative affinities among North and South American elements of subsectionCellulata.