See text Amaranthus is a cosmopolitan group of more than 50 species which make up the genus of annual or short-lived perennial plants collectively known as amaranths.

Its denominations in the languages of the peoples cultivating it since ancient times in America are huauhtli in Nahuatl,[11] kiwicha, ataĉo in Quechua,[12] tez or xtes in Maya, ahparie in Purépecha, wa've in Huichol, and guegui in Tarahumara.

[5] Flowers vary interspecifically from the presence of 3 or 5 tepals and stamens, whereas a 7-porate pollen grain structure remains consistent across the family.

[5] Species across the genus contain concentric rings of vascular bundles, and fix carbon efficiently with a C4 photosynthetic pathway.

[14] Amaranth grain contains phytochemicals that are not defined as nutrients and may be antinutrient factors, such as polyphenols, saponins, tannins, and oxalates.

[19] The support for the addition of the subdivision Albersia because of its indehiscent fruits coupled with three elliptic to linear tepals to be exclusive characters to members of this subgenus.

The classification of these groups are further supported with a combination of floral characters, reproductive strategies, geographic distribution, and molecular evidence.

[22] There is near certainty that A. hypochondriacus is the common ancestor to the cultivated grain species, however the later series of domestication to follow remains unclear.

[29] Amaranth weed species have an extended period of germination, rapid growth, and high rates of seed production,[3] and have been causing problems for farmers since the mid-1990s.

[30] The following 9 species of Amaranthus are considered invasive and noxious weeds in the U.S. and Canada: A. albus, A. blitoides, A. hybridus, A. palmeri, A. powellii, A. retroflexus, A. spinosus, A. tuberculatus, and A. viridis.

[3] Palmer amaranth is among the "top five most troublesome weeds" in the southeast of the United States and has already evolved resistances to dinitroaniline herbicides and acetolactate synthase inhibitors.

Proper weed control needs to be applied before the species successfully colonizes in the crop field and causes significant yield reductions.

An evolutionary lineage of around 90 species within the genus has acquired the C4 carbon fixation pathway, which increases their photosynthetic efficiency.

[38] Uncooked amaranth grain by weight is 12% water, 65% carbohydrates (including 7% dietary fiber), 14% protein, and 7% fat (table).

To this day, amaranth grains are toasted much like popcorn and mixed with honey, molasses, or chocolate to make a treat called alegría, meaning "joy" in Spanish.

[48][49] The earliest archeological evidence for amaranth in the Old World was found in an excavation in Narhan, India, dated to 1000–800 BCE.

[50] Because of its importance as a symbol of indigenous culture, its palatability, ease of cooking, and a protein that is particularly well-suited to human nutritional needs, interest in amaranth seeds (especially A. cruentus and A. hypochondriacus) revived in the 1970s.

It is a popular snack in Mexico, sometimes mixed with chocolate or puffed rice, and its use has spread to Europe and other parts of North America.

[13] Archeological evidence of seeds from A. hypochondriacus and A. cruentus[verification needed] found in a cave in Tehuacán, Mexico, suggests amaranth was part of Aztec civilization in the 1400s.

[54] Evidence from single-nucleotide polymorphisms and chromosome structure supports A. hypochondriacus as the common ancestor of the three grain species.

[60] In Indonesia and Malaysia, leaf amaranth is called bayam (although the word has since been loaned to refer to spinach, in a different genus[61]).

In Tamil Nadu, it is called mulaikkira and is regularly consumed as a favourite dish, where the greens are steamed and mashed with light seasoning of salt, red chili pepper, and cumin.

In the states of Andhra Pradesh and Telangana and other Telugu speaking regions of the country, this leaf is called as "Thotakura" and is cooked as a standalone curry, added as a part of mix leafy vegetable curry or added in preparation of a popular dal called thotakura pappu (తోటకూర పప్పు) in (Telugu).

In Brazil, green amaranth was, and to a degree still is, often considered an invasive species as all other species of amaranth (except the generally imported A. caudatus cultivar), though some have traditionally appreciated it as a leaf vegetable, under the names of caruru or bredo, which is consumed cooked, generally accompanying the staple food, rice and beans.

Making up about 5% of the total fatty acids of amaranth, squalene[65] is extracted as a vegetable-based alternative to the more expensive shark oil for use in dietary supplements and cosmetics.

[67] The genus also contains several well-known ornamental plants, such as Amaranthus caudatus (love-lies-bleeding), a vigorous, hardy annual with dark purplish flowers crowded in handsome drooping spikes.

Another Indian annual, A. hypochondriacus (prince's feather), has deeply veined, lance-shaped leaves, purple on the under face, and deep crimson flowers densely packed on erect spikes.

People decorated their homes and trees with paper flags; ritual races, processions, dances, songs, prayers, and finally human sacrifices were held.

[68][69] John Milton's Paradise Lost portrays a showy amaranth in the Garden of Eden, "remov'd from Heav'n" when it blossoms because the flowers "shade the fountain of life".