Common names: Common Pigweed, Redroot Pigweed
Lambs Quarters (Chenopodium album) are occasionally also called Pigweed or Smooth Pigweed but does not belong to the Amaranthaceae family. Common pigweed is often confused with other similar pigweed species. Smooth Pigweed is very similar but has terminal panicles that appear less dense, compact, and bristly than those of Common Pigweed. Palmer Amaranth (Amaranthus palmeri) also resembles Common and Smooth pigweed, but the terminal panicles of this species is much longer and narrower than the other pigweed species. This species may also resemble Common Lambs Quarters (Chenopodium album) in the cotyledon stage, but Lambs Quarter's cotyledons often have a mealy grey cast and the first true leaves are alternate, unlike any of the pigweed species.
The pigweed family contains many genera and over 500 species, including Common pigweed, Powell Amaranth, Prostrate Pigweed, and Tumble Pigweed, the most most common being Common Pigweed. Pigweeds are annual plants that germinate from seeds from late winter through summer.
The Common Pigweed is a common weed found throughout the world, and in particular in Europe, the USA, Brazil, Korea, Spain, Mozambique, Mexico, Hungary, Germany, and Afghanistan.
The Common Pigweed is an erect summer annual that may reach 2 m in height. The stems are stout, erect, and branched, usually with short hairs, especially near the upper portions of the plant. The plant has a shallow taproot that is often reddish in colour.
The leaves are grey-green and oval-spear-shaped, and covered with dense coarse hair. Red or light green stripes run along the length of the tall main stem. Seeds are in bushy spikes at the top of the plant and in the axils of the leaves. Although pigweed is primarily an upright grower, it will lie near the ground with constant mowing.
The flowers are greenish-grey, inconspicuous, and are produced in dense, compact, terminal panicles that are approximately 2 cm wide and from 5 to 20 cm in length. They are mixed with bristle-like bracts. Smaller inflorescences also occur between the stem and the leaf axils. Male and female flowers occur on the same plant (monoecious). Common pigweed flowers in high summer and fall, very shortly after germination, and deposits thousands of seeds during a single season, producing over 100,000 seeds/plant. The seeds are small, shiny, and black.
Seedlings of all Pigweeds are similar, with leaves that are long and narrow, and often red underneath. Prostrate pigweed forms dense mats and the leaves have distinctive light coloured edges. Tumble pigweeds have flowers in leaf axils rather than in spikes and have smaller leaves.
The Common Pigweed is found in horticultural, nursery, and agronomic crops, landscapes, roadsides, and also in pastures and forages.
North American Indians used A. retroflexus for flour and warm drinks.
Pigweed contains a nephrotoxin that causes kidney failure, and also contains soluble oxalates and is capable of accumulating nitrates. Therefore, toxicity can be due to any combination of these toxicoses.
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In 100 Thai individuals who were diagnosed with allergic rhinitis by history and clinical presentation who underwent a prick skin test with 30 aeroallergens:TREES: acacia 19%, mango 16%, coconut 12%. GRASSES: bermuda 17%, johnson 21%, timothy 16%, bahia 16% orchard 18%. WEEDS: pigweed 16%, kochia 14%. MOLDS: alternaria 11%, cladosporium 11%, aspergillus 12%, penicillium 16%, helminthosporium 16%, botrytis 15%, rhodotorula 20%, fusarium 26%, curvularia 26%, smut mix 11%, rust 9%. EPIDERMALS: cat 29%, dog 28%, feathers 37%. INDOOR ALLERGENS: house dust 72%, D. pteronyssinus 76%, D. farinae 79%, American cockroach 60%, German cockroach 41%, kapok 30%. Eighty-five percent of patients sensitive to house dust mites were positive to both D. pteronyssinus and D. farinae. (Pumhirun 1997 ref.2256 8)
Pumhirun P, Towiwat P, Mahakit P. Aeroallergen sensitivity of Thai patients with allergic rhinitis. Asian Pac J Allergy Immunol 1997;15(4):183-5
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Pigweed contains a nephrotoxin that causes kidney failure in animals, and also contains soluble oxalates and is capable of accumulating nitrates. Therefore, toxicity can be due to any combination of these toxicoses. (Torres 1997 ref.13287 4)
Torres MB, Kommers GD, Dantas AF, de Barros CL. Redroot pigweed (Amaranthus retroflexus) poisoning of cattle in southern Brazil. Vet Hum Toxicol 1997 Apr;39(2):94-6.
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