Index of Species Information
SPECIES: Amaranthus retroflexus
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Rough pigweed with seedhead. ©2005 Luigi Rignanese.
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Introductory
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:
https://www.fs.usda.gov/database/feis/plants/forb/amaret/all.html [].
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
DISTRIBUTION AND OCCURRENCE
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
MANAGEMENT CONSIDERATIONS
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].
BOTANICAL AND ECOLOGICAL CHARACTERISTICS
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].
FIRE ECOLOGY
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)
FIRE EFFECTS
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
REFERENCES
SPECIES: Amaranthus retroflexus
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