Weed Technology. 1997. Volume 11:199-202

Intriguing World of Weeds iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii

Redroot Pigweed ( us retroftexus )1

LARRY W. MITICH2

" ... To the ground, the dry unwithering nature of their showy . In Eu­ With solemn adoration, down they cast rope, such species are regarded as emblems of immor­ tality (Blatchley 1930). Their crowns, inwove with amaranth and gold. The species name comes from the Latin, retro, retro­ Immortal amaranth, a flower which once flexus, directed backwards and downwards (Gledhill In Paradise, fast by the tree of life, 1989). The mature flower head in redroot pigweed has a characteristic backward bend (Zimdahl 1989). Began to bloom." Thomas G. Fessendon is credited with the first use of -John Milton (1608-1676), Paradise Lost the word pigweed in the English language, but it prob­ ably applied to Chenopodium. In his Original Poems, revised edition published in 1806, he wrote: "The hya­ INTRODUCTION cinth and daffodil, / With now and then a big weed, / Reclroot pigweed (Amaranthus retroflexus L.), one of Of purslain and of weed." The next recorded use the New World's major weeds, was described in 1753 was in 1835 when Joseph H. Ingraham used it in The · by Carolus Linnaeus in Species Plantarum. Over three South-West, by a Yankee, two volumes, where he stated: decades later (1789), the genus was placed in Amaran­ "A weed not unlike the common pig-weed" (Simpson thaceae by Antoine Laurent de Jussieu (1748-1836) and Weiner 1989). (Britton and Brown 1898). belongs to Centrospermae, a group of families that contains betalain pigments instead of the anthocyanins found in most other HISTORY angiosperms; it is closely related to Chenopodiaceae / (Heywood 1993). Originally, the inhabited mountain and des- Depending upon circumscription, ert canyons, riverbanks, lakeshores, tidal marshes, and Amaranthaceae encompasses from 60 open beaches. Subsequently, humans increased the range to 70 genera and 900 widespread and of the genera in North and South America as new areas mostly tropical and temperate spe­ were colonized (Sauer 1967). cies; they are chiefly herbs (Brummitt As cultivated , grain amaranths are inextricably 1992; Heywood 1993; Mabberley involved in the history of the weedy ones. They are all 1989). The family contains several of New World origin. Aztecs in the 15th and 16th cen­ important horticultural species, in­ turies grew amaranths as a major grain crop, along with cluding cockscomb (Celosia argentea maize (Zea mays L.) and beans (Phaseolus spp.). The L. var. cristata Kuntz) and love-lies-bleeding (Amaran- seeds also were ground, made into a dough, and fash­ thus caudatus L.) (Heywood 1993), and grains (Hyam ioned into religious idols (Sauer 1950). Amaranth seeds and Pankhurst 1995). appear in archaeological sites from diverse cultures Amaranthus is derived from the Greek, a, not, mar­ (King 1966). Smooth pigweed (Amaranthus hybridus L.) aino, to wither, and anthos, a flower; the flowers do not is presumed to be the progenitor of A. cruentus L., which change or fade in some species (Darlington 1859; Hyam was originally selected as a grain crop in southern Mex­ and Pankhurst 1995). Contemporary Greeks call certain ico or Guatemala. Additionally, it was used as a dye Amaranthus spp. never fading or everlasting because of and ornamental. Pigweed seeds from an ancient Native American 1 No. 56 of the series "Intriguing World of Weeds." 2 Extension Weed Scientist Emeritus, Department of Vegetable Crops, campsite near Albuquerque, NM, were determined to be University of California, Davis, CA 95616. 6,800 years old (Apogino 1957). These seeds are at least

199 MITICH: REDROOT PIGWEED

roadsides, and other open, disturbed habitats where an­ nual weeds predominate, it seldom grows in shade. Fre­ quently, it is a contaminant in crop seed (Feltner 1970). Redroot pigweed is found in 46 countries. It is con­ sidered a serious weed in 16 countries, including Canada and Mexico, a principal weed in 16 additional countries, including the U.S., a common weed in two countries, and is present in 12 others (Holm et al. 1979). It was introduced from tropical America (Gates 1941; Muenscher 1955). Although the history of its spread is obscure, it is now common across the North American continent (Montgomery 1964). It also has been intro­ duced into Europe, the Middle East, North Africa, Japan, Redroot pigweed, Amaranthus retrojlexus L. China, , Russia, New South Wales, and New Zea­ land (Frankton and Mulligan 1970; Sauer 1967). 2,400 years older than samples of maize found on other 4,000-year-old sites (King 1966). USES Many Amaranthus spp. are used as pot herbs, wild or DESCRIPTION cultivated grains, ornamentals, and dyes, particularly in Redroot pigweed is a roughish, somewhat pubescent Central and South America and Asia, where some are annual, with a long, fleshy, red or pinkish taproot and still being grown (Heywood 1993). A. albus L. is eaten pink or white rootlets. Stems often are erect, 0.1 to 2 m in various tropical countries (Mabberley 1989). A. cruen­ high, simple or branching freely if not crowded, greenish tus L. and A. caudatus L. furnish edible grains (Mab­ to slightly reddish, the lower part thick and the smooth berley 1989; Sauer 1967) that are high in extractable upper part often very hairy; leaves are alternate, long­ protein, digestibility, and nutritive value (Holm et al. stalked, sparsely hairy, ovate to rhombic-ovate, dull 1977). Indeed, the protein-rich seeds (high in lysine) and green above, the lower surface with prominent white leaves of A. caudatus were widely used once as human veins (Gates 1941; Georgia 1942; Pammel and King food in the Andes, but eventually it was displaced by 1926; Weaver and McWilliams 1980). cereals (Heywood 1993). Pigweed is monoecious, with numerous small, green Redroot pigweed has been a favorite among Indians flowers crowded into dense, finger-like spikes forming a and was cultivated or encouraged to grow nearby. The long terminal panicle. Each flower is enclosed by one to copious small black seeds were collected by stacking three stiff awl-shaped bracts, up to 6 mm long, giving a mature plants on canvas or rocks to dry. Then the ma­ bristly appearance to the thick, stiff terminal panicle. terial was shaken and beaten to dislodge the seeds, which Overall, the terminal panicle is 5 to 20 cm long and 1.5 were separated from the chaff and winnowed (Harring­ cm or more thick, with smaller spikes in leaf axils below. ton and Matsumura 1967). They parched the seeds and Flowers haye either one pistil or five stamens, and five ate them whole, but the tiny seeds are difficult to chew. tepals in male flowers. They are predominantly wind­ More commonly, the seeds were ground into a meal, pollinated, although insects may pollinate under certain often mixed with cornmeal, and used in making bread, circumstances (Frankton and Mulligan 1970; Montgom­ cakes, mush, or gruel. The seeds also can be popped like ery 1964). popcorn. In times of emergency, the seeds provide a food Each flower produces a single oval, flattened, dark of great importance (Harrington and Matsumura 1967). brown or jet-black, smooth and shining seed (Georgia Native Americans considered the young shoots and 1942). The top of the fruit (utricle) falls away as a lid stems a favorite green. They also were eaten by early , (Blatchley 1930; Muenscher 1955). Seeds are minute, white settlers, and in recent times, by interested parties. being only 1 to 1.2 mm in diameter. The plant is cooked and ,served like spinach (Spinacia oleracea L.). The flavor is rather mild but very pleasant. DISTRIBUTION Also, young plants may be served raw as a salad (Har­ Redroot pigweed is one of the most common weeds rington and Matsumura 1967). of cultivated fields, orchards, gardens, waste places, While all Amaranthus spp. may cause livestock poi-

200 Volume 11, Issue I (January-March) 1997 WEED TECHNOLOGY soning when consumed in large amounts, they do not of long-lived seeds that are easily wind-dispersed (King cause human disorders when eaten in moderation (Har­ 1966; Spencer 1968; Thornton and Harrington n.d.), and rington and Matsumura 1967). in winter are blown far and wide over the snow (Blatch­ ley 1930). In Beal's Michigan buried seed experiment, seeds buried at a depth of 45 cm remained viable for 40 POISONOUS PRINCIPALS yr (Darlington and Steinbauer 1961). Redroot pigweed is as palatable to sheep (Ovis aries) Redroot pigweed seeds mature over a period of sev­ as oats (Avena sativa L.) and has a nutrient composition eral months. High temperatures (optimum 30 to 40 C) and digestibility equivalent to that of high quality alfalfa and adequate soil moisture are necessary for seeds to (Medicago sativa L.); it could be an acceptable forage germinate throughout the summer months. Even from a (Marten and Anderson 1975). However, Amaranthus single plant, seeds may differ in dormancy characteris­ spp. may accumulate high levels of nitrates, depending tics and germination requirements, depending upon tem­ upon the stage of development and environmental con­ perature and photoperiod during maturation (Barton ditions. 1962). The genus also causes allergic reactions in humans Pigweed has an extremely high potential rate of in­ (Weaver and McWilliams 1980). While redroot pigweed crease. A vigorous plant may produce 100,000 seeds. has been incriminated in cases of livestock loss (Kings­ The seeds are dispersed not only by wind, but also by bury 1964 ), stock usually eat it without harmful effects. animals after ingestion, and as contaminants of crop However, under certain conditions, especially high soil seeds or farm machinery. Hauptli and Jain (1978) re­ fertility, the plant may store nitrates in toxic amounts, ported that redroot pigweed grown in rows 25 cm apart causing bloat in grazing (Bos spp.) (Frankton and with 13 cm between plants produced an average of Mulligan 1970). 34,600 seeds per plant in fertilized field plots and 13,860 In drought years during autumn, redroot pigweed can per plant in unfertilized ones. be very toxic to horses (Equus caballus) and cattle (Gates 1941). Nitrates are stored primarily in the stems and branches, and the rate of nitrate absorption increases LITERATURE CITED as the plant matures (Woo 1919). The greatest concen­ Apogino, G. A. 1957. Pigweed seeds dated oldest U.S. food grain. Sci. News tration of nitrates occurs just before flowering (Campbell Letter (Wash.) 72:345. Barton, L. V. 1962. The germination of weed seeds. Weeds 10:174-182. 1924), but disappears at full maturity (King 1966). Blatchley, W. S. 1930. The Indiana Weed Book. Indianapolis: Nature Pub­ lishing. 191 p. Britton, N. L. and A. Brown. 1898. An Illustrated Flora of the Northern United WEEDINESS States, Canada and the British Possessions. Volume I. New York: Charles Scribner's Sons. 612 p. Redroot pigweed, common on cultivated land, reduces Brummitt, R. K. 1992. Families and Genera. London: Royal Botanic Gardens, Kew. 804 p. the yield of a variety of crops by competition (Mc­ Campbell, E.G. 1924. Nitrogen content of weeds. Bot. Gaz. 78:103-II5. Laughlin et al. 1976). Its long seed vitality is one reason Darlington, H. T. and G. P. Steinbauer. 1961. The eighty-year period for Dr. Beal's seed viability experiment. Am. J. Bot. 48:321-325. for its constant recurrence; the seeds are known to sur­ Darlington, W. 1859. American Weeds and Useful Plants. New York: Orange vive in soil for more than 30 yr. The seeds overwinter Judd. 460 p. Feltner, K. C. 1970. The ten worst weeds of field crops. 5. Pigweed. Crops either on or below the soil surface (Georgia 1942). For­ Soils 23: 13-14. merly, redroot pigweed was widely distributed in clover Frankton, C. and G. A. Mulligan. 1970. Weeds of Canada. Ottawa, ON: seeds (Pammel and King 1926). Queen's Printer. 217 p. Gates, F. C. 1941. Weeds in Kansas. Topeka, KS: Kansas State Board of Because of pigweed's indeterminate growth habit, it Agriculture. 360 p. often initiates elongated from the lateral Georgia, A. 1942. Manual of Weeds. New York: Macmillan. 593 p. Gledhill, D. 1989. The Names of Plants. 2nd ed. Cambridge, Great Britain: leaf axils once the terminal panicle is damaged. And it Cambridge University Press. 202 p. may assume an almost prostrate growth form in case of Harrington, H. D. and Y. Matsumura. 1967. Edible Native Plants of the Rocky Mountains. Albuquerque, NM: University of New Mexico Press. 392 p. extreme disturbance. The spiny-tipped bracts surround­ Hauptli, H. and S. K. Jain. 1978. Biosystematics and agronomic potential of ing the flowers possibly serve to protect developing some weedy and cultivated amaranths. Theor. Appl. Genet. 52: 177-185. seeds from predators (King 1966). When soil is moist, Heywood, V. H. 1993. Flowering Plants of the World. New York: Oxford University Press. 335 p. redroot pigweed transplants easily under ordinary farm Holm, L. G., J. V. Pancho, J. P. Herberger, and D. L. Plucknett. 1979. A tillage methods (Gates 1941). Also, pigweed resprouts Geographical Atlas of World Weeds. New York: J. Wiley. 391 p. Holm, L. G., D. L. Plucknett, J. V. Pancho, and J. P. Herberger. 1977. The easily from its taproot. World's Worst Weeds, Distribution and Biology. Honolulu, HI: Univer­ Redroot pigweed plants produce a prodigious number sity Press of Hawaii. 609 p.

Volume 11, Issue I (January-March) 1997 201 MITICH: REDROOT PIGWEED

Hyam, R. and P. Pankhurst. 1995. Plants and Their Names, A Concise Dic­ Sauer, J. D. 1950. The grain amaranths: a survey of their history and classi­ tionary. Oxford, Great Britain: Oxford University Press. 545 p. fication. Ann. Mo. Bot. Gard. 37:561-632. King, L. J. 1966. Weeds of the World. New York: Interscience Publishers. Sauer, J. D. 1967. The grain amaranth and their relatives: a revised taxonomic 526 p. and geographic survey. Ann. Mo. Bot. Gard. 54:103-137. Kingsbury, J. M. 1964. Poisonous Plants of the United States and Canada. Simpson, J. A. and E.S.C. Weiner. 1989. The Oxford English Dictionary. 2nd Englewood Cliffs, NJ: Prentice-Hall. 626 p. ed. Oxford, Great Britain: Clarendon Press. Mabberley, D. J. 1989. The Plant-Book. Cambridge, Great Britain: Cambridge - University Press. 706 p. Spencer, E. R. 1968. All About Weeds. New York: Dover Publications. 333 p. Marten, G. C. and R. N. Anderson. 1975. Forage nutritive value and palat­ Thornton, B. J. and H. D. Harrington. n.d. Weeds of Colorado. Agricultural ability of twelve common annual weeds. Crop Sci. 15:821-827. Experiment Station, Bull. 514-S. Fort Collins, CO: Colorado State Uni­ McLaughlin, M. F., R. D. Sweet, and S. Shannon. 1976. Weeds and crop versity. 218 p. growth Chenopodium album, Amaranthus retroj/exus, kidney beans. Weaver, S. E. and E. L. McWilliams. 1980. The biology of Canadian weeds. Proc. Annu. Meet. Northeast. Weed Sci. Soc. 30:105-117. 44. Amaranthus retrojiexus L., A. powellii S. and A. hybridus L. Can. J. Montgomery, F. H. 1964. Weeds of Canada and the Northern United States. Plant Sci. 60:1215-1234. Toronto: Ryerson Press. 266 p. Woo, M. L. 1919. Chemical constituents of Amaranthus retrojiexus. Bot. Gaz. Muenscher, W. C. 1955. Weeds. New York: Macmillan. 560 p. 68:313-344. Pammel, L. H. and C. M. King. 1926. The Weed Aora of Iowa. Des Moines, Zimdahl, R. L. 1989. Words and Words. Ames, IA: Iowa State University IA: State of Iowa. 715 p. Press. 125 p.

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