BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Amaranthus retroflexus | Rough Pigweed 



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].

Related categories for Species: Amaranthus retroflexus | Rough Pigweed