Index of Species Information

SPECIES:  Amaranthus retroflexus
Rough pigweed with seedhead. ©2005 Luigi Rignanese.


SPECIES: Amaranthus retroflexus
AUTHORSHIP AND CITATION : Walsh, Roberta A. 1993. Amaranthus retroflexus. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: [].
ABBREVIATION : AMARET SYNONYMS : NO-ENTRY SCS PLANT CODE : AMRE COMMON NAMES : rough pigweed redroot pigweed redroot amaranth green amaranth pigweed wild beet pigweed amaranth canne red-root pigweed careless weed TAXONOMY : The currently accepted scientific name of rough pigweed is Amaranthus retroflexus L. [11,14,18,20]. It is a member of the pigweed family (Amaranthaceae). There are no recognized subspecies, varieties, or forms. LIFE FORM : Forb FEDERAL LEGAL STATUS : No special status OTHER STATUS : NO-ENTRY


SPECIES: Amaranthus retroflexus
GENERAL DISTRIBUTION : Rough pigweed is found throughout North America, from Canada to Mexico, and from the Atlantic to the Pacific coasts. It is also found throughout much of the rest of the world, including Europe, South America, Eurasia, and Africa. It is a native of tropical America [11,14,18,19,27,35,43]. ECOSYSTEMS : Rough pigweed occurs in most ecosystems STATES : AL AK AZ AR CA CO CT DE FL GA ID IL IN IA KS KY LA ME MD MA MI MN MS MO MT NE NV NH NJ NM NY NC ND OH OK OR PA RI SC SD TN TX UT VT VA WA WV WI WY AB BC MB NB NS ON PE PQ SK MEXICO BLM PHYSIOGRAPHIC REGIONS : 1 Northern Pacific Border 2 Cascade Mountains 3 Southern Pacific Border 4 Sierra Mountains 5 Columbia Plateau 6 Upper Basin and Range 7 Lower Basin and Range 8 Northern Rocky Mountains 9 Middle Rocky Mountains 10 Wyoming Basin 11 Southern Rocky Mountains 12 Colorado Plateau 13 Rocky Mountain Piedmont 14 Great Plains 15 Black Hills Uplift 16 Upper Missouri Basin and Broken Lands KUCHLER PLANT ASSOCIATIONS : Rough pigweed occurs in most Kuchler Plant Associations. SAF COVER TYPES : Rough pigweed occurs in most SAF Cover Types. SRM (RANGELAND) COVER TYPES : Rough pigweed occurs in most SAF Cover Types. HABITAT TYPES AND PLANT COMMUNITIES : NO-ENTRY


SPECIES: Amaranthus retroflexus
IMPORTANCE TO LIVESTOCK AND WILDLIFE : Rough pigweed affects the kidneys of swine and cattle when animals consume large quantities of fresh material for 5 to 10 days. Cattle have developed perirenal edema and toxic nephrosis after ingesting rough pigweed. The toxicant has not been identified, although oxalates and/or phenolics have been suspected [37]. Additionally, rough pigweed accumulates nitrates, which causes poisoning in most livestock species when ingested in large quantities either fresh or in hay [6,21,44]. The excess nitrates cause cattle to bloat [41]. In the Midwest, pigs have been poisoned by rough pigweed growing under drought stress. In drought conditions, rough pigweed accumulation of nitrates accelerates [28,49]. In Nebraska, cattle consumed immature leaves and tops of rough pigweed in fields seeded to big bluestem (Andropogon gerardii var. gerardii). By mid-July of the first year of the study, nitrate concentration had reached toxic levels (10,000 ppm). In the second year, nitrate levels exceeded the toxic level at the beginning of the grazing season [23]. Sheep in Texas were maintained for varying lengths of time on rough pigweed pasture supplemented with wheat and alfalfa hays [15]. Scaled quail in Texas made use of rough pigweed seeds. When available, seeds averaged 0.9 percent of food eaten. In the highest recorded use, rough pigweed seeds made up 3.6 percent of food eaten. Percent use was greater than rough pigweed presence [1]. PALATABILITY : Rough pigweed is probably unpalatable when mature because of the stiff, spine-like bracts in the flower clusters. In Utah, rough pigweed was rated as having fair palatability for cattle and horses, and good palatability for sheep [7]. In Minnesota, rough pigweed was as palatable to sheep as oats (Avena sativa) [25]. NUTRITIONAL VALUE : Rough pigweed seeds with hulls contain 18.0 percent protein [29]. The nutritional components of immature rough pigweed browse are [29]: Component Percent Ash 18.8 Crude Fiber 10.8 N-free Extract 43.2 Protein 25.7 The use that various animals can make of protein in rough pigweed browse is [29]: Percent Animal Digestible Protein Cattle 19.7 Goats 20.5 Horses 19.3 Rabbits 18.5 Sheep 20.9 The food value of rough pigweed for wildlife species in several western states is rated as follows [7]: North Dakota Utah Wyoming Pronghorn good fair poor Elk fair poor Mule deer good good poor White-tailed deer good poor Small Mammals fair good Small nongame birds good good Upland game birds good fair good Waterfowl good poor fair In Minnesota, rough pigweed harvested from late June to mid-July showed a nutrient composition and digestibility for sheep equivalent to that of high-quality alfalfa (Medicago sativa). Rough pigweed contained adequate minerals to meet the requirements of ruminants. However, it must be utilized at relatively early stages of maturity. Nitrate concentration, which has been implicated in livestock poisoning, is highest in rough pigweed just before bloom. Calcium to potassium ratio in rough pigweed is such that it should not be fed as the sole ration [25]. COVER VALUE : The degree to which rough pigweed provides environmental cover for wildlife species in several western states is as follows [7]: North Dakota Utah Wyoming Pronghorn good poor poor Elk poor poor Mule deer good poor poor White-tailed deer good poor Small mammals fair fair Small nongame birds fair fair Upland game birds poor poor poor Waterfowl fair poor poor VALUE FOR REHABILITATION OF DISTURBED SITES : NO-ENTRY OTHER USES AND VALUES : Young leaves of rough pigweed are used as salad greens when the plant is only a few inches tall, before the stem becomes woody. Fresh young plants can also be used as a potherb. Seeds are edible whole or ground into meal. However, because rough pigweed concentrates nitrates, it should be used in moderation, particularly when taken from nitrate-fertilized areas [9]. OTHER MANAGEMENT CONSIDERATIONS : Rough pigweed is a useful component of patchwork vegetation for scaled quail habitat, providing both food and cover [1]. Rough pigweed is difficult to eradicate when once established [34]. A survey of weeds in spring annual crops throughout Manitoba over a 4-year period showed 83 weed species. Rough pigweed was the third most common dicotyledonous weed [40]. In Kansas, it was the most abundant forb weed in the seedbank [24]. Rough pigweed can be controlled with herbicides [30]. Cultivation reduces longevity of rough pigweed seed, apparently by increasing soil aeration, exposing the seeds to light, and generally improving conditions for germination. High soil temperatures favor germination and reduce rough pigweed seed survival [8]. Rough pigweed showed no establishment in intact prairie vegetation in an Illinois study. It did, however, establish in gaps in prairie vegetation. Flowering and seed set increased with increasing gap size [26]. An investigation was conducted in Nebraska as to the effect of cattle grazing in controlling rough pigweed and other weeds in seeded grassland. Cattle consumed immature rough pigweed, but nitrate accumulation limited grazing rough pigweed as a weed control practice [23].


SPECIES: Amaranthus retroflexus
GENERAL BOTANICAL CHARACTERISTICS : Rough pigweed is an introduced, coarse, monoecious, annual herb with taproots. It has an erect stem, 1 to 6.6 feet (0.3-2 m) tall, that is commonly freely branched. Leaves are 0.8 to 3.9 inches (2-10 cm) long. Inflorescences are usually densely crowded. There are often additional dense clusters of flowers in the axils of upper leaves. The fruit is a utricle [11,14,18,19,34]. Rough pigweed has a taproot. In pinyon-juniper (Pinus-Juniperus) woodland in New Mexico, root depth averaged 39 inches (100 cm), with a range of 3.9 to 95 inches (10-240 cm) [12]. RAUNKIAER LIFE FORM : Therophyte REGENERATION PROCESSES : Rough pigweed regenerates from seed each year. Plants can result from germination of newly released seed, or from germination of seed carried over in the seedbank from previous years. Seeds may germinate any time soil moisture is adequate during the growing season [44]. Rough pigweed seeds harvested in Mississippi showed 94 percent viability at time of harvest. After burial in soil for 30 months, seeds showed 7 percent viability. Seeds put in dry, low-temperature storage for 30 months had 98 percent viability [8]. Some seeds of rough pigweed remained viable after 24 hours of rumen digestion, 8 weeks ensiling, or both [4]. SITE CHARACTERISTICS : Rough pigweed grows in cultivated fields, gardens, orchards, fallow land, stream valleys, shores, prairie ravines, roadsides, fence rows, and waste places [17,34,35,43,47]. Its grows in dry to moist conditions [7]. In Utah, rough pigweed demonstrated poor growth on gravel, dense clay, and sodic-saline soils; fair growth on sandy, clay-loam, organic acidic, and saline soils; and good growth on sandy loam, loam, and clay. Optimum soil depth was 10 to 20 inches (25-50 cm) [7]. Recorded elevations for rough pigweed are [7]: State Elevation (feet) Elevation (m) Arizona 5,000-7,000 1,525-2,134 Colorado 4,700-9,200 1,433-2,804 Montana 2,300-9,000 700-2,743 Utah 4,400-4,700 1,341-1,433 Wyoming 4,300-7,800 1,310-2,377 SUCCESSIONAL STATUS : Obligate Initial Community Species Rough pigweed, an early successional species, extracts more nitrogen from and grows faster on the nitrogen-poor soils of recently abandoned fields than mid- and late successional species [38]. In Michigan, an agricultural field was rototilled and abandoned in March. By May, seedlings of several annuals had emerged. Dominant species during the first growing season included rough pigweed. In similar adjacent fields that had been abandoned for 5 and 15 years, rough pigweed was not present. [16]. During the 1934 drought, rough pigweed grew thickly where windblown dust had covered considerable portions of prairies in Kansas and Nebraska. Rough pigweed and other ruderals normally not found in prairies became widely distributed when released from their usual competition with grasses. However, with the end of drought and the return of grasses, rough pigweed nearly disappeared in many prairies [45]. SEASONAL DEVELOPMENT : Rough pigweed normally begins growth in late spring and matures in late summer or early fall [44]. It blooms in the Great Plains from July to October [14], and in the central and northeastern United States and adjacent Canada from August to October [11]. It blooms in southern California from June to November [27], in Montana from June to October, in North Dakota and Wyoming from July to September [7] and in the Carolinas from July until frost [31].


SPECIES: Amaranthus retroflexus
FIRE ECOLOGY OR ADAPTATIONS : Rough pigweed seeds are an important part of the seedbank in many habitats, even when plants are almost absent [16]. As an obligate initial community species, rough pigweed needs bare, disturbed sites in order to establish [26,38]. A fire which clears away competing vegetation can allow the establishment of rough pigweed. Rough pigweed seeds are very small [14], and easily blown by the wind from off-site sources. Some seeds survive cattle digestion [4], and can be carried by animals to burned areas. FIRE REGIMES : Find fire regime information for the plant communities in which this species may occur by entering the species name in the FEIS home page under "Find Fire Regimes". POSTFIRE REGENERATION STRATEGY : Ground residual colonizer (on-site, initial community) Initial-offsite colonizer (off-site, initial community)


SPECIES: Amaranthus retroflexus
IMMEDIATE FIRE EFFECT ON PLANT : NO-ENTRY DISCUSSION AND QUALIFICATION OF FIRE EFFECT : NO-ENTRY PLANT RESPONSE TO FIRE : When rough pigweed is killed by fire, the population must establish from seed. If a fire in the spring kills rough pigweed plants but conditions continue to be favorable, seeds from the seedbank will germinate [44]. Late in the growing season, a fire will prepare the seedbed for establishment of rough pigweed from seed the next spring. DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : NO-ENTRY FIRE MANAGEMENT CONSIDERATIONS : NO-ENTRY


SPECIES: Amaranthus retroflexus
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