Amaranthus, collectively known as amaranth, is a cosmopolitan genus of annual or short-lived perennial plants. Some amaranth species are cultivated as leaf vegetables, pseudocereals, and ornamental plants. Most of the species from Amaranthus are summer annual weeds and are commonly referred to as pigweed.maranth seeds contain lysine, an essential amino acid, limited in grains or other plant sources. Most fruits and vegetables do not contain a complete set of amino acids, and thus different sources of protein must be used. Amaranth too is limited in some essential amino acids, such as leucine and threonine.