Identifying the weedy amaranths (Amaranthus, Amaranthaceae) of South America

Abstract

Background: Amaranthus is a genus of Amaranthaceae with ca. 75 species. Many of them are of economic importance as cultivated crops (grains or vegetables) or ornamentals, while around 20 range from significant weeds to minor ones. Objective: List and differentiate the species (and subspecies) of weeds that belong to genus Amaranthus and range in South America. Results: Thirteen species and four subspecies of Amaranthus are considered weeds in South America; six of them are of great importance (A. blitum, A. deflexus, A. hybridus, A. palmeri, A. spinosus, and A. viridis), while the rest cause minor damage. Vernacular names, distribution, diagnoses, notes, and vouchers are given for every taxon. Conclusions: Within the 13 species of weeds that belong to genus Amaranthus in South America, there are two among the worst noxious weeds in the world: A. hybridus (with two subspecies), which ranges in many countries of this continent, and A. palmeri, present up to now only in Argentina. Other four important weeds are widespread in different countries: A. blitum (with two subspecies), A. deflexus, A. spinosus, and A. viridis.