This paper is the first in a projected series of publications treating the Chenopodiaceae in South America. We present here a taxonomic revision of subfamilies Betoideae, Camphorosmoideae, and Salsoloideae in South America, where all representatives of these subfamilies are introduced. Our research is based on the study of herbarium material, type specimens, digital images, original publications, and field observations. The South American Chenopodiaceae flora includes only Beta vulgaris L. from Betoideae, Bassia hyssopifolia (Pall.) Kuntze, Bassia scoparia (L.) A. J. Scott, and Maireana brevifolia (R. Br.) P. G. Wilson from Camphorosmoideae, and Salsola kali L., Salsola tragus L., and Soda inermis Fourr. from Salsoloideae. Lectotypes for Echinopsilon reuterianus Boiss., Kochia alata Bates, K. parodii Aellen, K. parodii var. elongata Aellen, K. parodii var. densa Aellen, K. parodii var. glabrescens Aellen, and Suaeda sieversiana Pall. are designated here, as well as a second-step lectotype for K. brevifolia R. Br. The distribution of all species is updated based on the revision and proper identification of many herbarium specimens and field observations. The distribution of M. brevifolia in Chile is here expanded. New synonyms for Bassia scoparia are proposed. A preliminary key to the genera of Chenopodiaceae in South America is also presented.