Amaranth
Amaranthus, collectively known as amaranth or pigweed, is a cosmopolitan genus of herbs. Approximately 60 species are presently recognised, with inflorescences and foliage ranging from purple and red to gold. Members of this genus share many characteristics and uses with members of the closely related genus Celosia.
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 ( or ) 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. This complicates taxonomy and Amaranthus has generally been considered among systematists as a difficult genus.
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.
In some cultures it was known as a mythical flower that never fades.

# Uses

## Grain amaranth
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. Amaranthus species are reported to have a 30% higher protein value than other cereals, such as rice, wheat flour, oats and rye.
Amaranth grain is a crop of moderate importance in the Himalaya.  It was one of the staple foodstuffs of the Incas, and it is known as kiwicha in the Andes today. It was also used by the ancient Aztecs, who called it huautli, and other Native America peoples in Mexico to prepare ritual drinks and foods. To this day, amaranth grains are toasted much like popcorn and mixed with honey or molasses to make a treat called alegria (literally "joy" in Spanish).
Amaranth was used in several Aztec ceremonies, where images of their gods (notably Huitzilopochtli) were made with amaranth mixed with honey. The images were cut to be eaten by the people. This looked like the Christian communion to the Roman Catholic priests, so the cultivation of the grain was forbidden for centuries.
Because of its importance as a symbol of indigenous culture, and because it is very palatable, easy to cook, and its protein particularly well suited to human nutritional needs, interest in grain amaranth (especially A. cruentus and A. hypochondriacus) was revived in the 1970s. It was recovered in Mexico from wild varieties and is now commercially cultivated.   It is a popular snack sold in Mexico City and other parts of Mexico, sometimes mixed with chocolate or puffed rice, and its use has spread to Europe and other parts of North America.  Amaranth and quinoa are called pseudograins because of their flavor and cooking similarities to grains.  These are dicot plant seeds, and both contain exceptionally complete protein for plant sources.  Besides protein, amaranth grain provides a good source of dietary fiber and dietary minerals such as iron, magnesium, phosphorus, copper, and especially manganese.

## Vegetables
Amaranth species are cultivated and consumed as a leaf vegetable in many parts of the world. There are 4 species of Amaranthus 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, while the Tagalogs in the Philippines call the plant kulitis. In Andhra Pradesh, India, this leaf is added in preparation of a popular dal called thotakura pappu. In China, the leaves and stems are used as a stir-fry vegetable and called yin choi (; pinyin: xiancai; and variations on this transliteration in various dialects). In Congo it is known as lenga lenga or biteku teku.
In the Caribbean the leaves are called callaloo and are sometimes used in a soup called pepperpot soup.
In East Africa Amaranth leaf is known in Swahili as mchicha ("a vegetable for all"). It is sometimes recommended by some doctors for people having low red blood cell count.
In West Africa, Nigeria, it is known in Yoruba as efo tete or arowo jeja ("we have money left over for fish"). It is a common vegetable, and it goes with all Nigerian carbohydrate dishes.

## Dyes
The flowers of the 'Hopi Red Dye' amaranth were used by the Hopi Amerindians as the source of a deep red dye.  There is also a synthetic dye that has been 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.

## Ornamentals
The genus also contains several well-known ornamental plants, such as A. caudatus (love-lies-bleeding), a native of India and 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 and various case-bearers 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).

# Nutritional value
Amaranth greens, also called Chinese spinach, hinn choy or yin tsoi (Template:Zh-stp), callaloo, thotakura (telugu) , tampala, or quelite, are a common leaf vegetable throughout the tropics and in many warm temperate regions. It is very popular in Andhra Pradesh. They are a very good source of vitamins including vitamin A, vitamin B6, vitamin C, riboflavin, and folate, and dietary minerals including calcium, iron, magnesium, phosphorus, potassium, zinc, copper, and manganese.  Because of its valuable nutrition, some farmers grow amaranth today.  However their moderately high content of oxalic acid inhibits the absorption of calcium and zinc, and also means that they should be avoided or eaten in moderation by people with kidney disorders, gout, or rheumatoid arthritis. Reheating cooked amaranth greens is often discouraged, particularly for consumption by small children, as the nitrates in the leaves can be converted to nitrites, similarly to spinach.
Amaranth seeds, like buckwheat and quinoa, contain protein that is unusually complete for plant sources. Most fruits and vegetables do not contain a complete set of amino acids, and thus different sources of protein must be used.
Several studies have shown that like oats, amaranth seed or oil may be of benefit for those with hypertension and cardiovascular disease; regular consumption reduces blood pressure and cholesterol levels, while improving antioxidant status and some immune parameters.  While the active ingredient in oats appears to be water soluble fiber, amaranth appears to lower cholesterol via its content of plant stanols and squalene.

# Amaranth as a weed
Not all amaranth plants are cultivated.  Most of the species from Amaranthus are summer annual weeds and are commonly referred to as pigweeds. These species have an extended period of germination, rapid growth, and high rates of seed production and have been causing farmers problems 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 strain of the Palmer amaranth has appeared which is Glyphosate-resistant and as a result cannot be killed by the widely used Roundup herbicide.  Also, this hardy plant can survive in tough conditions.  This could be of particular concern to cotton farmers using Roundup Ready cotton. 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 and has already evolved resistances to dinitroanilines and acetolactate synthase inhibitors. This makes the proper identification of Amaranthus species at the seedling stage essential for agriculturalists.  Proper herbicide treatment needs to be applied before the species successfully colonizes in the crop field and causes significant yield reductions.
Anecdotal reports indicate that some people are allergic to amaranth.

# Myth, legend and poetry
Amaranth, or Amarant (from the Greek amarantos, unwithering), a name chiefly used in poetry, and applied to Amaranth and other plants which, from not soon fading, typified immortality.
Aesop's Fables (6th century BC) compares the Rose to the Amaranth to illustrate the difference in fleeting and everlasting beauty.
Thus, in John Milton's Paradise Lost (1667), iii. 353:
Samuel Taylor Coleridge, in Work without Hope (1825), also references the herb, likely referencing Milton's earlier work. (ll 7-10 excerpted):
The original spelling is amarant; the more common spelling amaranth seems to have come from a folk etymology assuming that the final syllable derives from the Greek word anthos ("flower"), common in botanical names.
In ancient Greece the amaranth (also called chrysanthemum and helichrysum) was sacred to Ephesian Artemis. It was supposed to have special healing properties, and as a symbol of 
immortality was used to decorate images of the gods and tombs. In legend, Amarynthus (a form of Amarantus) was a hunter of Artemis and king of Euboea; in a village of Amarynthus, of which he was the eponymous hero, there was a famous temple of Artemis Amarynthia or Amarysia (Strabo x. 448; Pausan. i. 31, p. 5). It was also widely used by the Chinese for its healing chemicals, curing illnesses such as infections, rashes, and migraines.  The "Amarantos" is the name of a several-century-old popular Greek folk song:
Finnish symphonic metal band Nightwish featured a song titled Amaranth on their 2007 album Dark Passion Play.
The Swedish doom/gothic band  Draconian have released a song called The Amaranth, where the plant is used as a symbol for the dark side of Venus.
Orson Scott Card's novel Speaker for the Dead features a plant called amaranth native to the planet Lusitania, where the majority of the story takes place.
In Vampire: The Masquerade lore, an amaranth placed on the bed of a vampire was the warning of Diablerie soon to come. The act of Diablerie was also referred to as "Amaranth".
Enya is referring to the everlasting amaranth in her song Amarantine.