Amaranth


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. Some names include "prostrate pigweed" and "love lies bleeding". Some amaranth species are cultivated as leaf vegetables, pseudocereals, and ornamental plants.
Catkin-like cymes of densely packed flowers grow in the summer or fall. 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 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, and the remaining 65 are monoecious species that are 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.

Names and etymology

The word amaranth derives from Ancient Greek ἀμάραντος, meaning “unfading”, a name used across cultures. Its development is associated with the Greek word for “flower”, ἄνθος, giving rise to the idea of the “unfading flower”. Amarant is an archaic variant of the name.
The botanical name Amaranthus likewise comes from the Ancient Greek ἀμάραντος. The noun is formed from the privative prefix ἀ-, meaning “without”, and the verb μαραίνω, meaning “to consume” or “to exhaust”. Classical references to the plant appear in the works of Dioscorides.
The name amaranth was first applied in Europe to the related genus Celosia. At the time, plants of the genus Amaranthus were not yet known in Europe. Amaranthus and Celosia share long-lasting dried flowers, which contributed to the transfer of the name.
Amaranth has long been associated with the idea of immortality. This symbolism is linked to the persistence of its calyx, which does not readily wither. For this reason, some species of amaranth are used in dry bouquets.
The Latin form amaranthus, which includes the letter h, arose from an erroneous association with the Greek word ἄνθος, meaning “flower”. This element appears in the names of many plants, such as Agapanthus, and influenced later botanical spelling.
In the languages of Indigenous peoples who cultivated amaranth in the Americas since ancient times, the plant is known by a variety of names. In Nahuatl, it is called huauhtli. In Quechua, it is known as kiwicha and ataĉo. In Maya, it is called tez or xtes. Additional names include ahparie in the Purépecha language, wa've in Huichol, and guegui in the Tarahumara.

Description

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 and of 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 or dioecious. Fruits are in the form of capsules referred to as a unilocular pixdio that opens at maturity. The top of the unilocular pixdio releases the urn that contains the seed. Seeds are circular form from 1 to 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.

Chemistry

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.

Taxonomy

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 is distinctive, the genus has few distinguishing characters among the 75 species present across six continents. This complicates taxonomy and Amaranthus has generally been considered among systematists as a "difficult" genus and to hybridize often.
In 1955, Sauer classified the genus into two subgenera, differentiating only between monoecious and dioecious species: Acnida Aellen ex K.R. Robertson and Amaranthus. Although this classification was widely accepted, further infrageneric classification was 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 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 using maximum parsimony and Bayesian analysis of nuclear and chloroplast genes suggest five groups within the genus:.
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 suggested classification. Bracteole morphology present on the stem is used for taxonomic classification of Amaranth. Wild species have longer bracteoles 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. caudatus, A. hypochondriacus, and A. quentiensis are native to Central and North America.

Species

Species include:
  • Amaranthus acanthochiton – greenstripe
  • Amaranthus acutilobus – a synonym of Amaranthus viridis
  • Amaranthus albus – white pigweed, tumble pigweed
  • Amaranthus anderssonii
  • Amaranthus arenicola – sandhill amaranth
  • Amaranthus australis – southern amaranth
  • Amaranthus bigelovii – Bigelow's amaranth
  • Amaranthus blitoides – mat amaranth, prostrate amaranth, prostrate pigweed
  • Amaranthus blitum – purple amaranth
  • †Amaranthus brownii – Brown's amaranth
  • Amaranthus californicus – California amaranth, California pigweed
  • Amaranthus cannabinus – tidal-marsh amaranth
  • Amaranthus caudatus – love-lies-bleeding, pendant amaranth, tassel flower, quilete
  • Amaranthus chihuahuensis – Chihuahuan amaranth
  • Amaranthus crassipes – spreading amaranth
  • Amaranthus crispus – crispleaf amaranth
  • Amaranthus cruentus – purple amaranth, red amaranth, Mexican grain amaranth
  • Amaranthus deflexus – large-fruit amaranth
  • Amaranthus dubius – spleen amaranth, khada sag
  • Amaranthus fimbriatus – fringed amaranth, fringed pigweed
  • Amaranthus floridanus – Florida amaranth
  • Amaranthus furcatus
  • Amaranthus graecizans
  • Amaranthus grandiflorus
  • Amaranthus greggii – Gregg's amaranth
  • Amaranthus hybridus – smooth amaranth, smooth pigweed, red amaranth
  • Amaranthus hypochondriacus – Prince-of-Wales feather, prince's feather
  • Amaranthus interruptus – Australian amaranth
  • Amaranthus minimus
  • Amaranthus mitchellii
  • Amaranthus muricatus – African amaranth
  • Amaranthus obcordatus – Trans-Pecos amaranth
  • Amaranthus palmeri – Palmer's amaranth, Palmer pigweed, careless weed
  • Amaranthus polygonoides – tropical amaranth
  • Amaranthus powellii – green amaranth, Powell amaranth, Powell pigweed
  • Amaranthus pringlei – Pringle's amaranth
  • Amaranthus pumilus – seaside amaranth
  • Amaranthus quitensis - Mucronate Amaranth
  • Amaranthus retroflexus – red-root amaranth, redroot pigweed, common amaranth
  • Amaranthus saradhiana - purpal stem amaranth, green leaf amaranth
  • Amaranthus scleranthoides – variously Amaranthus sclerantoides
  • Amaranthus scleropoides – bone-bract amaranth
  • Amaranthus spinosus – spiny amaranth, prickly amaranth, thorny amaranth
  • Amaranthus standleyanus
  • Amaranthus thunbergii – Thunberg's amaranth
  • Amaranthus torreyi – Torrey's amaranth
  • Amaranthus tricolor – Joseph's-coat
  • Amaranthus tuberculatus – rough-fruit amaranth, tall waterhemp
  • Amaranthus viridis – slender amaranth, green amaranth
  • Amaranthus watsonii – Watson's amaranth
  • Amaranthus wrightii – Wright's amaranth