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 Amaranthus species are summer annual weeds and are commonly referred to as pigweed.Catkin-like cymes of densely packed flowers grow in summer or autumn. Amaranth varies in flower, leaf, and stem color with a range of striking pigments from the spectrum of maroon to crimson and can grow longitudinally from 3 to 8 feet tall with a cylindrical, succulent, fibrous stem that is hollow with grooves and bracteoles when mature.
There are approximately 75 species in the genus, 10 of which are dioecious and native to North America with the remaining 65 monoecious species endemic to every continent from tropical lowlands to the Himalayas. Members of this genus share many characteristics and uses with members of the closely related genus Celosia. Amaranth grain is collected from the genus. The leaves of some species are also eaten.
"Amaranth" derives from Greek  (amárantos), "unfading", with the Greek word for "flower", (ánthos), factoring into the word's development as amaranth, the unfading flower. Amarant is an archaic variant. The showy Amaranth present in John Milton's garden of Eden is "remov'd from Heav'n" when it blossoms because the flowers "shade the fountain of life". He describes Amaranth as 'immortal' in reference to the flowers that generally do not whither and retain bright reddish tones of color, even when deceased as sometimes referred to as "love-lies-bleeding."
Amaranth is a herbaceous plant or shrub that is either annual or perennial across the genus. 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. Species across the genus contain concentric rings of vascular bundles, and fix carbon efficiently with a C4 photosynthetic pathway. Leaves are approximately 6.5-15 centimetres (2.6-5.9 in) oval or elliptical shape that are either opposite or alternate across species, although most leaves are whole and simple with entire margins.
Amaranth has a primary root with deeper spreading secondary fibrous root structures.Inflorescences are in the form a large panicle that varies from terminal to axial, color, and sex. The tassel of fluorescence is either erect or bent and varies in width and length between species. Flowers are radially symmetric and either bisexual or unisexual with very small, bristly perianth and pointy bracts. Species in this genus are either monecious (i.e. A. hybridus, L.) or dioecious (i.e. A. arenicola, L.). Fruits are in the form of capsules referred to as a unilocular pixdio that opens at maturity. The top (operculum) of the unilocular pixdio releases the urn that contains the seed. Seeds are circular form from 1-1.5 millimeters in diameter and range in color with a shiny, smooth seed coat. The panicle is harvested 200 days after cultivation with approximately 1,000 to 3,000 seeds harvested per gram.
Amaranthus shows a wide variety of morphological diversity among and even within certain species. Amaranthus is part of the Amaranthaceae that is part of the larger grouping of the Carophyllales. Although the family (Amaranthaceae) is distinctive, the genus has few distinguishing characters among the 75 species present across all seven continents. This complicates taxonomy and Amaranthus has generally been considered among systematists as a "difficult" genus and hybridize often.
In 1955, Sauer classified the genus into two subgenera, 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. Mosyakin and Robertson 1996 later divided into three subgenera: Acnida, Amaranthus, and Albersia. The support for the addition of the subdivision Albersia because of its circumcise, 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.
The phylogenies of Amaranthus of maximum parsimony and Bayesian analysis of nuclear and chloroplast genes suggest five clades within the genus: Diecious / Pumilus, Hybris, Galapagos, Eurasian/ South African, Australian (ESA), ESA + South American.
Amaranthus includes three recognised subgenera and 75 species, although species numbers are questionable due to hybridisation and species concepts. Infrageneric classification focuses on inflorescence, flower characters and whether a species is monoecious/dioecious, as in the Sauer (1955) suggested classification. Bracteole morphology present on the stem is used for taxonomic classification of Amaranth. Wild species have longer bracteole's compared to cultivated species. A modified infrageneric classification of Amaranthus includes three subgenera: Acnida, Amaranthus, and Albersia, with the taxonomy further differentiated by sections within each of the subgenera.
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. There has been opposing hypotheses of a single as opposed to multiple domestication events of the three grain species. There is evidence of phylogenetic and geographical support for clear groupings that indicate separate domestication events in South America and Central America.A. hybridus may derive from South America, whereas A. quentiensis, A. caudatus, and A. hypochondriacus are native to Central and North America.
Uncooked amaranth grain is 12% water, 65% carbohydrates (including 7% dietary fiber), 14% protein, and 7% fat (table). A 100 grams (3.5 oz) reference amount of uncooked amaranth grain provides 371 calories, and is a rich source (20% or more of the Daily Value, DV) of protein, dietary fiber, pantothenic acid, vitamin B6, folate, and several dietary minerals (table). Uncooked amaranth is particularly rich in manganese (159% DV), phosphorus (80% DV), magnesium (70% DV), iron (59% DV), and selenium (34% DV). Cooking decreases its nutritional value substantially across all nutrients, with only dietary minerals remaining at moderate levels. Cooked amaranth leaves are a rich source of vitamin A, vitamin C, calcium, and manganese, with moderate levels of folate, iron, magnesium, and potassium. Amaranth does not contain gluten.
Amaranth grain contains phytochemicals that are not defined as nutrients and may be antinutrient factors, such as polyphenols, saponins, tannins, and oxalates. These compounds are reduced in content and antinutrient effect by cooking.
The genus is native to Mexico and Central America. Known to the Aztecs as hu?uhtli, amaranth is thought to have represented up to 80% of their energy consumption before the Spanish conquest. Another important use of amaranth throughout Mesoamerica was in ritual drinks and foods. 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. Diego Durán described the festivities for the Aztec god Huitzilopochtli (whose name means "left side of the hummingbird"; hummingbirds feed on amaranth flowers). The Aztec month of Panquetzaliztli (7 December to 26 December) was dedicated to Huitzilopochtli. People decorated their homes and trees with paper flags; ritual races, processions, dances, songs, prayers, and finally human sacrifices were held. This was one of the more important Aztec festivals, and the people prepared for the whole month. They fasted or ate very little; a statue of the god was made out of amaranth seeds and honey, and at the end of the month, it was cut into small pieces so everybody could eat a piece of the god. After the Spanish conquest, cultivation of amaranth was outlawed, while some of the festivities were subsumed into the Christmas celebration.
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 was recovered in Mexico from wild varieties and is now commercially cultivated. It is a popular snack in Mexico, sometimes mixed with chocolate or puffed rice, and its use has spread to Europe and parts of North America. Amaranth and quinoa are pseudocereals because of their similarities to cereals in flavor and cooking.
Several species are raised for amaranth "grain" in Asia and the Americas. The spread of Amaranthus is of a joint effort of human expansion, adaptation, and fertilization strategies. Seeds of Amaranth grain have been found in archeological records in Northern Argentina that date to the mid-Holocene. Archeological evidence of seeds from A. hypochondriacus and A. crutenus found in a cave in Tehuacan, Mexico suggests Amaranth was part of Aztec civilization in the 1400s.
Ancient amaranth grains still used include the three species, Amaranthus caudatus, Amaranthus cruentus, and Amaranthus hypochondriacus. Evidence from single-nucleotide polymorphisms and chromosome structure supports A. hypochondriacus as the common ancestor of the three grain species.
It has been proposed as an inexpensive native crop that could be cultivated by indigenous people in rural areas for several reasons:
In the United States, amaranth crop is mostly used for seed production. Most amaranth in American food products starts as a ground flour, blended with wheat or other flours to create cereals, crackers, cookies, bread or other baked products. Despite utilization studies showing that amaranth can be blended with other flours at levels above 50% without affecting functional properties or taste, most commercial products use amaranth only as a minor portion of their ingredients despite them being marketed as "amaranth" products.
Amaranth species are cultivated and consumed as a leaf vegetable in many parts of the world. Four species of Amaranthus are documented as cultivated vegetables in eastern Asia: Amaranthus cruentus, Amaranthus blitum, Amaranthus dubius, and Amaranthus tricolor.
In Indonesia and Malaysia, leaf amaranth is called bayam. In the Philippines, the Ilocano word for the plant is kalunay; the Tagalog word for the plant is kilitis or kulitis. In Uttar Pradesh and Bihar in India, it is called chaulai and is a popular green leafy vegetable (referred to in the class of vegetable preparations called saag). It is called chua in Kumaun area of Uttarakhand, where it is a popular red-green vegetable. In Karnataka in India, it is called harive. It is used to prepare curries such as hulee, palya, majjigay-hulee, and so on. In Kerala, it is called cheera and is consumed by stir-frying the leaves with spices and red chili peppers to make a dish called cheera thoran. 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. It is called keerai masial. In Andhra Pradesh, this leaf is added in preparation of a popular dal called thotakura pappu in (Telugu). In Maharashtra, it is called shravani maath and is available in both red and white colour. In Orissa, it is called khada saga, it is used to prepare saga bhaja, in which the leaf is fried with chili and onions.
In China, the leaves and stems are used as a stir-fry vegetable, or in soups. In Vietnam, it is called rau d?n and is used to make soup. Two species are popular as edible vegetable in Vietnam: d?n (Amaranthus tricolor) and d?n c?m or d?n tr?ng (Amaranthus viridis).
In Bantu regions of Uganda and western Kenya, it is known as doodo or litoto. It is also known among the Kalenjin as a drought crop (chepkerta). In Lingala (spoken in the Congo), it is known as l?ngal?nga or bít?kut?ku. In Nigeria, it is a common vegetable and goes with all Nigerian starch dishes. It is known in Yoruba as shoko a short form of shokoyokoto (meaning "make the husband fat") or arowo jeja (meaning "we have money left over for fish"). In the Caribbean, the leaves are called bhaji in Trinidad and callaloo in Jamaica, and are sautéed with onions, garlic, and tomatoes, or sometimes used in a soup called pepperpot soup. In Botswana, it is referred to as morug and cooked as a staple green vegetable.
In Greece, green amaranth (A. viridis) is a popular dish called , vlita or vleeta. It is boiled, then served with olive oil and lemon juice like a salad, sometimes alongside fried fish. Greeks stop harvesting the plant (which also grows wild) when it starts to bloom at the end of August.
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.
The flowers of the 'Hopi Red Dye' amaranth were used by the Hopi (a tribe in the western United States) as the source of a deep red dye. Also a synthetic dye was named "amaranth" for its similarity in color to the natural amaranth pigments known as betalains. This synthetic dye is also known as Red No. 2 in North America and E123 in the European Union.
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.
Amaranths are recorded as food plants for some Lepidoptera (butterfly and moth) species including the nutmeg moth and various case-bearer moths of the genus Coleophora: C. amaranthella, C. enchorda (feeds exclusively on Amaranthus), C. immortalis (feeds exclusively on Amaranthus), C. lineapulvella, and C. versurella (recorded on A. spinosus).
Amaranth weed species have an extended period of germination, rapid growth, and high rates of seed production, and have been causing problems for farmers since the mid-1990s. This is partially due to the reduction in tillage, reduction in herbicidal use and the evolution of herbicidal resistance in several species where herbicides have been applied more often. 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.
A new herbicide-resistant strain of Amaranthus palmeri has appeared; it is glyphosate-resistant and so cannot be killed by herbicides using the chemical. Also, this plant can survive in tough conditions. The species Amaranthus palmeri (Palmer amaranth) causes the greatest reduction in soybean yields and has the potential to reduce yields by 17-68% in field experiments. 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. This makes the proper identification of Amaranthus species at the seedling stage essential for agriculturalists. 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. This probably occurred in the Miocene.
Love-lies-bleeding (Amaranthus caudatus)
Spiny amaranth (Amaranthus spinosus)
Green amaranth (Amaranthus viridis)
Southern Kerala-style traditional Thoran made with Cheera (amaranth) leaves
Amaranth from Chilpancingo