You are here
Species
Amaranthus retroflexus L. (1753)
IUCN
NCBI
EOL Text
Stem erect, light green, 20-80 cm tall, stout, branched or not, slightly obtusely angulate, densely pubescent. Petiole light green, 1.5-5.5 cm, hairy; leaf blade ovate-rhombic or elliptic, 5-12 × 2-5 cm, both surfaces shortly hairy, but densely hairy abaxially, base cuneate, margin entire and undulate, apex acute or notched, with a mucro. Complex thyrsoid structures terminal and axillary, erect, 2-4 cm in diam., including many spikes; terminal spikes longer than lateral ones. Bracts and bracteoles white, subulate, 4-6 mm, apex slenderly long pointed. Tepals white, oblong or oblong-obovate, 2-2.5 mm, membranous, with a green midvein, apex acute or notched, with a mucro. Stamens slightly longer than perianth. Stigmas 3, rarely 2. Utricles light green, ovoid, compressed, shorter than perianth, circumscissile. Seeds brown or black, subglobose, ca. 1 mm in diam., obtuse at margin. Fl. Jul-Aug, fr. Aug-Sep. 2n = 32*, 34*, 102*.
| License | http://creativecommons.org/licenses/by-nc-sa/3.0/ |
| Rights holder/Author | eFloras.org Copyright © Missouri Botanical Garden |
| Source | http://www.efloras.org/florataxon.aspx?flora_id=2&taxon_id=200006986 |
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.
Amaranthus retroflexus, native to central and eastern North America, is a successful invasive species and has effectively colonized a wide range of habitats on all inhabited continents. Its variability is extremely wide; usually the species is easily recognized and its identification causes no specific problems. Infraspecific entities described within A. retroflexus are mostly ecologic variants of little or no taxonomic value. Two varieties are more easily recognized: the common var. retroflexus, with bracts about 1.5-2 times as long as tepals, and a more rare var. delilei (Richter & Loret) Thellung (= A. delilei Richter & Loret), with bracts 1-1.5 times as long as tepals.
Occasional forms morphologically intermediate between Amaranthus retroflexus and taxa of the A. hybridus aggregate (e.g., A. powellii and A. hybridus, in the strict sense) are known both in the Americas and the Old World. Usually such plants are treated as hybrids; in many cases they are probably just extremes of the natural variability of A. retroflexus. Putative hybrids of A. retroflexus were described from Europe as A. ×ozanonii Thellung (A. hybridus × A. retroflexus) and A. ×soproniensis Priszter & Karpáti (A. powellii × A. retroflexus) (see A. Thellung 1914-1919; S. Priszter 1958; P. Aellen 1959; F. Grüll and S. Priszter 1973).
| License | http://creativecommons.org/licenses/by-nc-sa/3.0/ |
| Rights holder/Author | eFloras.org Copyright © Missouri Botanical Garden |
| Source | http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=200006986 |
Plants densely to moderately pubescent, especially distal parts of stem and branches. Stems erect, reddish near base, branched in distal part to simple 0.2-1.5(-2) m; underdeveloped or damaged plants rarely ascending to nearly prostrate. Leaves: petiole 1/2 to equaling blade; blade ovate to rhombic-ovate, 2-15 × 1-7 cm, base cuneate to rounded-cuneate, margins entire, plane or slightly undulate, apex acute, obtuse, or slightly emarginate, with terminal mucro. Inflorescences terminal and axillary, erect or reflexed at tip, green or silvery green, often with reddish or yellowish tint, branched, leafless at least distally, usually short and thick. Bracts lanceolate to subulate, (2.5-)3.5-5(-6) mm, exceeding tepals, apex acuminate with excurrent midrib. Pistillate flowers: tepals 5, spatulate-obovate, lanceolate-spatulate, not clawed, subequal or unequal, (2-)2.5-3.5(-4) mm, membranaceous, apex emarginate or obtuse, with mucro; style branches erect or slightly spreading,; stigmas 3. Staminate flowers few at tips of inflorescences; tepals 5; stamens (3-)4-5. Utricles broadly obovoid to broadly elliptic, 1.5-2.5 mm, shorter than or subequal to tepals, smooth or slightly rugose, especially near base and in distal part, dehiscence regularly circumscissile. Seeds black to dark reddish brown, lenticular to subglobose-lenticular, 1-1.3 mm, smooth, shiny.
| License | http://creativecommons.org/licenses/by-nc-sa/3.0/ |
| Rights holder/Author | eFloras.org Copyright © Missouri Botanical Garden |
| Source | http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=200006986 |
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.
One of us (Clemants) does not recognize the following varieties.
| License | http://creativecommons.org/licenses/by-nc-sa/3.0/ |
| Rights holder/Author | eFloras.org Copyright © Missouri Botanical Garden |
| Source | http://www.efloras.org/florataxon.aspx?flora_id=2&taxon_id=200006986 |
Amaranthus retroflexus var. salicifolius I. M. Johnston
| License | http://creativecommons.org/licenses/by-nc-sa/3.0/ |
| Rights holder/Author | eFloras.org Copyright © Missouri Botanical Garden |
| Source | http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=200006986 |
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].
rough pigweed
redroot pigweed
redroot amaranth
green amaranth
pigweed
wild beet
pigweed amaranth
canne
red-root pigweed
careless weed
This adventive plant is a summer annual about 1-3' tall that is either sparingly branched or unbranched. The central stem is stout, round, light green, and more or less covered with white hairs; it also has fine longitudinal veins that are white. The alternate leaves are up to 6" long and 4" across (excluding the petioles), becoming smaller in the upper half of the central stem. They are cordate-ovate or elliptic and smooth or slightly undulate along the margins. The base of each leaf is rounded or wedge-shaped, while its tip is rounded and blunt. The lower surface of each leaf is usually pubescent, while the upper surface is less pubescent or hairless. The central stem terminates in a stout panicle of spikes with whitish green flowers. This terminal inflorescence is up to 6" long (rarely longer in large plants). There are also shorter axilllary panicles of flowering spikes or simple spikes that develop from the axils of the middle to upper leaves. The flowering spikes are bristly in appearance from the crowded flowers and pointed bracts. Rough Pigweed is usually monoecious with separate pistillate (female) and staminate (male) flowers on the same plant. The pistillate flowers have 5 pale white sepals, an ovary with 3 styles, and no petals. The staminate flowers have 5 pale white sepals, 5 stamens, and no petals. The sepals are oblong and about 3 mm. in length; their tips are either short and pointed or flattened. At the base of each flower, there are one or more green bracts about 3-6 mm. long. These bracts have long pointed tips. The blooming period occurs from late summer to early fall and lasts about 1-2 months. Cross-pollination of the flowers is by wind. Each pistillate flower develops a single seed in a membranous bladder (utricle). This utricle splits up to release the seed. Each small seed is dark brown or black, flattened, and circular; it has a smooth and shiny surface. The root system consists of a short stout taproot that is usually tinted red. This plant spreads by reseeding itself. Cultivation
| License | http://creativecommons.org/licenses/by-nc/3.0/ |
| Rights holder/Author | Copyright © 2002-2014 by Dr. John Hilty |
| Source | http://www.illinoiswildflowers.info/weeds/plants/rgh_pigweed.htm |