• Key characteristics
  • Biology
  • Impacts
  • Control
  • Further information

  • Eleven species of amaranth have been found in New Zealand, all introduced from tropical or subtropical regions. Some species were cultivated as ornamental garden plants and have then escaped. Others are limited in their distribution
  • All species grow as weeds in dry places, around towns and cities and especially in waste places and near docks and rail yards. Some are also serious weeds of summer crops, notably maize
  • Originating from warm countries, amaranths tend to germinate in late spring, grow and flower in the summer. Almost all of the species found here are annual species and die after flowering or with the first frosts
  • Amaranths are C4 plants, meaning that their photosynthesis pathways produce 4-carbon sugars rather than 3-carbon sugars. They can tolerate warmer and drier conditions than our winter-growing species.

Redroot (Amaranthus powellii or Amaranthus retroflexus)

  • These two species have often been confused in New Zealand
  • Amaranthus powellii is common or abundant in both North and South Islands, in waste and cultivated land particularly close to built-up areas
  • Amaranthus retroflexus grows in similar habits and is particularly common in the South Island and in parts of the North Island
  • Both species are more or less hairy, 80-100 cm tall although small plants of both species grow in impoverished places. Stems are red towards the base (hence the common name)
  • The best way to distinguish the two species is the shape of the apex of the female tepals: Amaranthus powellii tepals are very unequal and end in sharp tips; Amaranthus retroflexus tips are blunt. In addition Amaranthus retroflexus has short lateral branches of the inflorescence densely arranged up the main spike, whilst in Amaranthus powellii the lateral branches form towards the base
  • Amaranthus powellii has been found to be responsible for nitrate poisoning in cattle; Amaranthus retroflexus is known to be responsible for poisoning pigs in the United States, but not in New Zealand
  • Both species used as vegetables in their native countries.

Prostrate amaranth (Amaranthus deflexus)

  • Abundant from the Waikato southwards but less common further north. Also common in Nelson, Marlborough, north and central Canterbury, but less southwards to Otago. Grows in waste places, in particular on shingle or gravel and around settled areas. It is becoming increasingly common in crops, especially under irrigation
  • Stems tend to lie on the ground, turning upwards at the ends, forming large leafy mats. Leaves are up to 5 cm long on long stalks. Flower head a terminal spike, with the lower lateral branches having short lateral spikes in the upper leaf axils. Stems and flower heads often tan or brown in colour, leaves occasionally with whitish ‘V’ shaped marking
  • Found in New Zealand first in 1896, probably arriving by accident from tropical America.

Purple amaranth (Amaranthus lividus)

  • Scattered throughout the North Island, especially in towns and cities in warmer areas.. Grows in waste places and cultivated areas but is not very common. Rare in the north of the South Island
  • Stems tend to lie along the ground. Leaves with slender petioles (stalks) which are about half the length of the leaf blades. Flower head a terminal spike, with short lateral spikes in the axils of the upper leaves. In New Zealand the flower heads are mostly bright green in colour whereas in Australia they are usually purple (hence the name)
  • First recorded in New Zealand in 1870, originating in tropical and sub-tropical species, where it is widespread.

Mat amaranth (Amaranthus graecizans)

  • An annual species, found in Auckland City and Dargaville, and around the East Cape, but most common in Central Otago. Grows in dry stony or gravelly waste places on roadsides and riverbanks
  • Plants are erect or spreading, much branched, hairless or almost, and up to 80 cm high. Flower heads are greenish, forming clusters in the axils of nearly all leaves
  • Found in New Zealand first in 1944, probably introduced from tropical Africa or the Mediterranean.

Green amaranth (Amaranthus viridis)

  • The most common amaranth in the tropical South Pacific and only found in New Zealand north of the Bay of Plenty, growing in crops and on sand dunes
  • A sprawling or partly erect annual plant up to 40 cm high, not very hairy except on the young stems
  • First observed in New Zealand in 1867.

Similar but less common species

  • Five other species of Amaranthus have been found in New Zealand, but one of these – Amaranthus spinosus ­– has only been recorded once and is not naturalised. The other species are Amaranthus albus (tumbleweed amaranth), found in and near Napier in the North Island and in Nelson and Christchurch, usually around docks and railway yards, especially where ballast has been dumped. Amaranthus caudatus (love-lies-bleeding) is a garden escape common in and around Christchurch and elsewhere in scattered locations. Easily recognised by its long, drooping, lime green or crimson-coloured, flower heads. It has rough-hairy leaves, leafy stems and beaked seeds and is sometimes common on roadsides and waste places in a few areas of North and South Islands. Amaranthus cruentus is widespread in the tropics as a crop used for its grain. It is tall-growing annual with spikes of dark pink flowers. In New Zealand it has been found growing wild near Masterton and at Rangiora, Lincoln and Waimate in Canterbury. Amaranthus hybridus has two recognised varieties here, one of which, var. erythrostachys, known as prince’s feather, is sometimes found as a garden plant and has escaped in a few places as a weed. It has crimson flowers. The other, var. hybridus, occurs only in a few places like parts of Auckland, Thames, and Mangatahi in Hawkes Bay.


  • All the species of Amaranthus originated in tropical and subtropical countries, some in North and Central America, some in Europe and Asia
  • Of the eleven species recorded from New Zealand most have been accidentally introduced in ballast or in seed or other vegetable matter from warm zones. Two or three species arrived in New Zealand as ornamental garden plants and have then escaped into the wild.

Life cycle

  • Most of the species found in New Zealand are annuals but one or two species can persist as short-lived perennials, especially in frost-free places
  • Being from the tropics or subtropics all species are sensitive to and killed by frosts.


  • Some species are used as ornamental garden plants and some are grown for their grain production
  • Many species of amaranth are cultivated as vegetables, for grain production or for animal food in warmer countries.

Impact on crops

  • Redroot in particular is a common weed of maize, mostly because it grows as the same time as the crop, but also because it grows quickly and can form large, aggressive plants, potentially at high densities
  • Prostrate amaranth is also found in some maize crops but is more common on lower growing vegetable and forage crops
  • Redroot and other species also often establish in orchards, in the bare, sprayed strip between the crop rows.

Impact on grazing animals

  • Some species of amaranth contain high levels of oxalates and, under certain conditions contain high levels of nitrate. Many poisonings of livestock in New Zealand are associated with high nitrate levels in redroot.

Grazing management

  • Livestock readily graze amaranth. Therefore, care is required when nitrate levels might be high.

Mowing management

  • Mowing plants taller than the crop, or where no desirable plants are present will give some control and may reduce seed production.

Management by cultivation

  • In cropping cultivation can be used to gain control, but these species tend to emerge at the same time as maize crops. Stale seed bed methods can be effective for later sown crops.

Chemical control

  • Redroot and other amaranth species are susceptible to most herbicides that do not affect the crop. In maize atrazine, acetochlor, mesotrione, nicosulfuron and topramezone are often used
  • In orchards or waste spaces glyphosate or glufosinate can both give good control
  • If using chlorsulfuron in cereals, amaranth seedlings should be treated when small
  • Trifluralin, applied and incorporated before the crop is sown, is effective
  • Some commonly used herbicides like clopyralid or ioxynil will not control these species.

  • Connor HE 1977. The poisonous plants in New Zealand. Government Printer, Wellington. 247 p.
  • Harrington KC 2016. Redroot. Massey University Weeds Database. (accessed 11 August 2016)
  • Popay I, Champion P, James T 2010. An illustrated guide to common weeds of New Zealand. New Zealand Plant Protection Society, Christchurch, New Zealand. 416 p.