Although several species are often considered weeds, people around the world value amaranths as leaf vegetables, cereals and ornamentals.

The word comes from the Greek amarantos (Αμάρανθος or Αμάραντος) the "one that does not wither," or the never-fading (flower).

Systematics

Amaranthus shows a wide variety of morphological diversity among and even within certain species. Although the family (Amaranthaceae) is distinctive, the genus has few distinguishing characters among the 70 species included. Juan et al (2007). Electrophoretic characterization of Amaranthus L. seed proteins and its systematic implication. Botanical Journal of the Linnean Society 155: 57-63. This complicates taxonomy and Amaranthus has generally been considered among systematists as a “difficult” genus. Costea, M & D. DeMason (2001). Stem morphology and anatomy in Amaranthus L. (Amaranthaceae)- Taxonomic significance. Journal of the Torrey Botanical Society 128(3): 254-281.

Formerly, Sauer (1955) classified the genus into 2 sub-genera, differentiating only between monoecious and dioecious species: Acnida (L.) Aellen ex K.R. Robertson and Amaranthus. Although this classification was widely accepted, further infrageneric classification was (and still is) needed to differentiate this widely diverse group.

Currently, Amaranthus includes 3 recognized sub-genera and 70 species, although species numbers are questionable due to hybridization and species concepts. Infrageneric classification focuses on inflorescence, flower characters and whether a species is monoecious/dioecious, as in the Sauer (1955) suggested classification. A modified infrageneric classification of Amaranthus was published by Mosyakin & Robertson (1996) and includes 3 subgenera: Acnida, Amaranthus and Albersia. The taxonomy is further differentiated by sections within each of the sub-genera.

Grain amaranth

A traditional food plant in Africa, this little-known vegetable has potential to improve nutrition, boost food security, foster rural development and support sustainable landcare.

Several species are raised for amaranth grain in Asia and the Americas. Ancient amaranth grains still used to this day include the 3 species, Amaranthus caudatus, Amaranthus cruentus, and Amaranthus hypochondriacus. Although amaranth was (and still is) cultivated on a small-scale in parts of Mexico, Guatemala, Peru, India, and Nepal, there is potential for further cultivation in the U.S and tropical countries and is often referred to as "the crop of the future." It has been proposed as an inexpensive native crop that could be cultivated by indigenous people in rural areas for several reasons: 1) easily harvested, 2) produces a lot of fruits (and thus seeds) which are used as grain, 3) highly tolerant of arid environments which are typical of most subtropical and some tropical regions, and 4) large amounts of protein and essential amino acids, such as lysine. Due to its weedy life history, amaranth grains grow very rapidly and their large seedheads can weigh up to 1 kilogram and contain a half-million seeds. Tucker, J. (1986). Amaranth: the once and future crop. Bioscience 36(1): 9-13. Amaranthus species are reported to have a 30% higher protein value than other cereals, such as rice, wheat flour, oats and rye.