The upper photograph displays the red form of Slender Pigweed. The 'redness' of individual plants can be quite variable – this is particularly true of the leaves, which can vary from green with dark purple blotches to to brilliant red. The flowering panicles and spikes are most likely to assume a bright red color. Another species that is often more or less red, Amaranthus cruentus (Red Amaranth), is occasionally cultivated as a garden plant. This species has been known to escape from cultivation, although this is uncommon. Some authorities regard Red Amaranth as a cultivated form Slender Amaranth, or Amaranthus hybridus cruentus. However, Mohlenbrock (2001) considers Red Amaranth a separate species that has bracts about 2-3 mm. in length and staminate flowers with only 3 stamens, rather than the usual 5. Another similar species, Amaranthus retroflexus (Rough Pigweed), is somewhat stouter and has longer bracts (about 4-6 mm.) than Slender Amaranth. To my knowledge, Rough Pigweed doesn't assume a red form.

This adventive plant is a summer annual about 2-4' tall. It is unbranched, or branches occasionally. The central stem is greenish tan to red, round in circumference, ribbed, and usually hairy; sometimes the lower portion of this stem is hairless. The alternate leaves are up to 4½" long and 2¾" across (excluding the petioles), becoming slightly smaller as they ascend the central stem. They are ovate orelliptic-ovate, smooth or slightly undulate along the margins, and pubescent or hairless. The lower side of each leaf has elevated pinnate veins. The uppermost leaves are smaller, lanceolate, and pubescent. This form of Slender Pigweed has predominately red foliage, although the leaves may be green with blotches of red. The petioles are quite long, causing the leaves to droop downward somewhat; they are often pubescent like the stems. The upper stem terminates in an elongated panicle of spikes with small reddish flowers. This panicle is up to 1½' long on large plants. From the axils of the upper leaves, there also develops panicles of spikes or simple spikes of flowers that are much shorter than the terminal inflorescence. The individual spikes have a bristly appearance because of the linear bracts surrounding the flowers. Slender Pigweed is usually monoecious with staminate and pistillate flowers on the same plant. Each type of flower has 5 pink sepals and no petals. The sepals are about 2 mm. in length and oblong with short pointed tips. Each staminate flower (male) has 5 stamens, while each pistillate flower (female) has an ovary with 3 styles. Each type of flower is surrounded by several red bracts that are about 3-4 mm. long and linear with long pointed tips. The blooming period occurs during late summer to early fall and lasts about 1-2 months. The flowers are wind-pollinated. Each flower is replaced by a seed that is contained in a bladder-like membrane (utricle). This utricle becomes brown and splits apart to release the seed. The small seeds are flattened, dark brown or black, circular, and shiny. They are produced in great abundance on a robust plant. The root system consists of a taproot that is short and stout; it is often tinted red. This plant spreads by reseeding itself.

This is the common green form of Slender Pigweed. Contrary to the scientific name, this species is not a hybrid, although it can hybridize with Amaranthus retroflexus (Rough Pigweed). These two species of Pigweed are both from South America and they are fairly difficult to tell apart. In this regard, a 10x hand lens can be helpful. Generally, the flowering spikes of Slender Amaranth are more green and slender than those of Rough Pigweed; the flowering spikes of the latter are whitish green and rather stout. The floral bracts of Slender Pigweed are about 3-4 mm., while the floral bracts of Rough Pigweed are about 4-6 mm. long. The sepals of Slender Pigweed usually have pointed tips, while the sepals of Rough Pigweed have tips that are more flattened. Rough Pigweed is generally more short and stout in its growth habit, and it is usually no more than 3' tall. Another common name for Amaranthus hybridus is Green Pigweed, but the foliage of this species is sometimes red.

This adventive plant is a summer annual about 2-6' tall. It is unbranched, or branches occasionally. The central stem is light green or tan-green, round in circumference, ribbed, and usually hairy; sometimes the lower portion of this stem is hairless. The alternate leaves are up to 5½" long and 3" across (excluding the petioles), becoming slightly smaller as they ascend the central stem. They are ovate or elliptic-ovate, smooth or slightly undulate along the margins, and pubescent or hairless. The lower side of each leaf has elevated pinnate veins. The uppermost leaves are smaller, lanceolate, and pubescent. This form of Slender Pigweed has predominately green foliage, although their may be red tints along the margins of the leaves and elsewhere. The petioles are quite long, causing the leaves to droop downward somewhat; they are often pubescent like the stems. The upper stem terminates in an elongated panicle of spikes with small green flowers. This panicle is up to 2' long on large plants. From the axils of the upper leaves, there develops panicles of spikes or simple spikes of flowers that are much shorter than the terminal inflorescence. The individual spikes have a bristly appearance because of the linear bracts surrounding the flowers. Slender Pigweed is usually monoecious with staminate and pistillate flowers on the same plant. Each type of flower has 5 cream sepals and no petals. The sepals are about 2 mm. in length and oblong with short pointed tips. Each staminate flower (male) has 5 stamens, while each pistillate flower (female) has an ovary with 3 styles. Each type of flower is surrounded by several green bracts that are about 3-4 mm. long and linear with long pointed tips. The blooming period occurs during late summer to early fall and lasts about 1-2 months. The flowers are wind-pollinated. Each flower is replaced by a seed that is contained in a bladder-like membrane (utricle). This utricle becomes tan and splits apart to release the seed. The small seeds are flattened, dark brown or black, circular, and shiny. They are produced in great abundance on a robust plant. The root system consists of a taproot that is short and stout; it is often tinted red. This plant spreads by reseeding itself.

Amaranthus patulus Bertol.:
China (Asia)

Canada

Origin: Exotic

Regularity: Regularly occurring

Currently: Unknown/Undetermined

Confidence: Confident

Canada

Origin: Exotic

Regularity: Regularly occurring

Currently: Unknown/Undetermined

Confidence: Confident

United States

Origin: Unknown/Undetermined

Regularity: Regularly occurring

Currently: Unknown/Undetermined

Confidence: Confident

Slender Pigweed is a common plant that has been observed in most counties of Illinois. The red form of this species is less common than the green form (the Distribution Map combines observations for both forms). Slender Pigweed is originally from South America. Habitats include weedy meadows, cropland, fallow fields, farm lots, vegetable gardens, gravelly areas along railroads, and waste areas. Highly disturbed areas are preferred; the red form of Slender Amaranth often occurs along railroads.

Slender Pigweed is a common plant that has been observed in most counties of Illinois. The green form of this species is more common than the red form (the Distribution Map combines observations for both forms). It is originally from South America. Habitats include weedy meadows, cropland, fallow fields, farm lots, vegetable gardens, gravelly areas along railroads, and waste areas. Highly disturbed and degraded habitats are preferred.

Amaranthus hybridus L.:
Argentina (South America)
Belize (Mesoamerica)
Bolivia (South America)
Brazil (South America)
Bhutan (Asia)
Canada (North America)
Mexico (Mesoamerica)
Honduras (Mesoamerica)
Peru (South America)
Panama (Mesoamerica)
Chile (South America)
Gabon (Africa & Madagascar)
Costa Rica (Mesoamerica)
Guatemala (Mesoamerica)
Ecuador (South America)
Laos (Asia)
Nepal (Asia)
Japan (Asia)
French Guiana (South America)
United States (North America)
China (Asia)
Vietnam (Asia)
Suriname (South America)
Venezuela (South America)

Amaranthus hybridus var. quitensis (Kunth) Covas:
Argentina (South America)

Amaranthus hybridus subsp. cruentus (L.) Thell.:
Gabon (Africa & Madagascar)
South Africa (Africa & Madagascar)

Amaranthus chlorostachys Willd.:
Argentina (South America)
Bolivia (South America)

One of us (Clemants) prefers to treat this as a synonym of Amaranthus cruentus.

Originally a riverside pioneer in eastern North America, now Amaranthus hybridus is extremely abundant in agricultural fields and other disturbed habitats. Related cultivated species have been reported from the flora area, including A. caudatus, A. hypochondriacus, and A. cruentus; there is no evidence that they are established; specimens identified as these species are often variants of A. hybridus. 

 Distribution of Amaranthus hybridus in North America needs clarification because the name was misapplied to other species, notably A. powellii, and specimens of A. retroflexus, A. powellii, and A. hybridus are frequently interchangeably misidentified. Forms of A. hybridus and A. powellii with reddish inflorescences are often misidentified as escaped and hence presumably naturalized, cultivated species A. caudatus Linnaeus, A. hypochondriacus Linnaeus, and A. cruentus Linnaeus.

Amaranthus hybridus is extremely variable. In particular, there are numerous North American specimens with subobtuse tepals and thick inflorescences, suggesting hybridization with A. retroflexus. In Europe such presumably hybrid forms are known as A. ×ozanonii Thellung (A. Thellung 1914-1919).

A new, presumably hybridogenous taxon, Amaranthus ×tucsonensis Henrickson, was recently described from Arizona (J. Henrickson 1999). It was suggested that one of its parents is A. hybridus; the other parental species (probably a species with obtuse or spatulate tepals) remains unknown. The problem of proper taxonomic position and origin of A. ×tucsonensis needs further study.

Stem to 2 m tall, glabrous or somewhat soft pubescent. Petiole 3-8 cm; leaf blade ovate to rhombic-ovate, 6-12 × 4-7 cm, pale and soft pubescent on abaxial veins, adaxially glabrous, base cuneate, margin entire or slightly undulate, apex acute to subobtuse. Complex thyrsoid structures terminal and in apical axils, greenish, the terminal to 25 cm, much branched, composed of many lateral spikes. Bracts green, 2-4 mm, membranous near base, long pointed. Tepals 5, oblong-lanceolate, slightly shorter than utricle, 1.5-2 mm, apex obtuse or slightly mucronulate. Stamens 5. Utricles compressed, circumscissile. Seeds black, shiny, ca. 1 mm in diam.

Annual herb, erect or less commonly ascending, up to c. 2 (-3) m in height, not infrequently reddish-tinted throughout. Stems stout, branched, angular, glabrous or thinly to moderately furnished with short or long multicellular hairs (increasingly so above, especially in the inflorescence). Leaves glabrous, or thinly pilose on the lower margins and underside of the primary nervation, long-petiolate (petioles up to 15 cm but even then scarcely exceeding the lamina), lamina broadly lanceolate to rhomboid or ovate, 3-19 (-30) x 1.5-8 (-12) cm, gradually narrowed to the blunt to subacute mucronulate tip, attenuate or shortly cuneate into the petiole below. Flowers in yellowish, green, reddish or purple axillary and terminal spikes formed of cymose clusters, which are increasingly closely approximate upwards, the terminal inflorescence varying from a single spike to a broad, much-branched, panicle up to c. 45 x 25 cm: in length and breadth, the ultimate spike not infrequently nodding; male and female flowers intermixed throughout the spikes. Bracts and bracteoles deltoid-ovate to deltoid-lanceolate, pale-membranous, acuminate and with a long, pale to reddish-tipped, erect arista formed by the stout, excurrent, yellow or greenish midrib, subequalling to much exceeding the perianth. Perianth segments (3-)5, 1.5-3.5 mm, lanceolate or oblong, acute-aristate or the inner sometimes blunt in the female flowers, only the midrib at most greenish. Stigmas (2-) 3, erect, flexuose or recurved, c. 0.75-1.25 mm. Capsule subglobose to ovoid or ovoid-urceolate, 2-3 mm, circumscissile, with a moderately distinct to obsolete “neck”, lid smooth, longitudinally sulcate, or sometimes rugulose below the neck. Seed black and shining or pale, compres¬sed, 0.75-1.25 mm, almost smooth centrally, faintly reticulate around the margins.

Stem 30-50 cm tall, branched, pubescent. Petiole 1-2.5 cm, hairy; leaf blade ovate or ovate-rhombic, 3-4.5 × 1.5-2.5 cm, abaxially pilose, adaxially nearly glabrous, base cuneate, margin undulate, apex acute or notched, with a mucro. Complex thyrsoid structures terminal, slender, somewhat drooping at apex and in spikes. Bracts and bracteoles subulate, lanceolate, 3.5-4 mm, distinctly long pointed, longer than perianth. Tepals oblong-lanceolate, ca. 2 mm, apex acute, with a mucro. Stamens nearly as long as or slightly longer than perianth; stigmas 3. Utricles ovoid, longer than perianth, ca. 2 mm, circumscissile. Seeds black, subglobose, ca. 1 mm in diam. Fl. Jul-Aug, fr. Sep-Oct. 2n = 24, 32*, 33, 34.

Plants glabrous or glabrescent, or distal parts of stem and branches slightly pubescent when young. Stems erect, green or sometimes reddish purple, rarely under-developed plants ascending, branched to nearly simple, 0.3-2(-2.5) m. Leaves: petiole ¹/2 as long as to equaling blade; blade ovate, rhombic-ovate, or lanceolate, (2-)4-15 × (1-)2-6 cm, base cuneate to broadly cuneate, margins entire, apex acute to obtuse, with mucro. Inflorescences terminal and axillary, erect or reflexed, occasionally nodding, green or olive green, occasionally with silvery or reddish purple tint, leafless at least distally, terrminal inflorescence often slightly nodding with numerous shorter branches at base. Bracts lanceolate-linear to subulate, 2-3.5(-4) mm, subequal to or 2 times as long as tepals }, apex spinescent. Pistillate flowers: tepals 5, lanceolate to lanceolate-linear, subequal or unequal, 1.5-3 mm, membranaceous, apex acute or acuminate, gradually narrowing into aristate tip; style branches erect, shorter than body of fruit; stigmas 3. Staminate flowers at tips of inflorescences; tepals 5; stamens (4-)5. Utricles obovoid or elongate-ovoid, 1.5-2.5 mm, shorter than tepals, smooth proximally, lid verrucose or rugose, dehiscence regularly circumscissile, or rarely in some presumably hybrid forms, irregularly dehiscent or indehiscent. Seeds black to dark reddish brown, lenticular to lenticular-globose, 1-1.3 mm, smooth, shiny.

Waste places, roadsides. Taiwan [native to tropical America].

Farms, waste places, hillsides. Anhui, Fujian, Guizhou, Henan, Hubei, Hunan, Jiangsu, Jiangxi, Shaanxi, Sichuan, Zhejiang [Bhutan, Japan, Laos, Nepal, Sikkim, Vietnam; Europe, North and South America].

Flowering summer-fall. Waste places, agricultural and fallow fields, railroads, roadsides, riverbanks, other disturbed habitats; 0-2500 m; B.C., Man., N.S., Ont., Que.; Ala., Ariz., Ark., Calif., Colo., Conn., Del., D.C., Fla., Ga., Idaho, Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Mont., Nebr., Nev., N.H., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Okla., Pa., R.I., S.C., S.Dak., Tenn., Tex., Vt., Va., Wash., W.Va., Wis.; Mexico; West Indies; Central America; South America; widely introduced or naturalized in tropical, subtropical, and warm-temperate regions worldwide.

Slender Pigweed is a common plant that has been observed in most counties of Illinois. The red form of this species is less common than the green form (the Distribution Map combines observations for both forms). Slender Pigweed is originally from South America. Habitats include weedy meadows, cropland, fallow fields, farm lots, vegetable gardens, gravelly areas along railroads, and waste areas. Highly disturbed areas are preferred; the red form of Slender Amaranth often occurs along railroads.

Slender Pigweed is a common plant that has been observed in most counties of Illinois. The green form of this species is more common than the red form (the Distribution Map combines observations for both forms). It is originally from South America. Habitats include weedy meadows, cropland, fallow fields, farm lots, vegetable gardens, gravelly areas along railroads, and waste areas. Highly disturbed and degraded habitats are preferred.

Insects rarely visit the wind-pollinated flowers. The caterpillars of the skipper Pholisora catullus (Common Sootywing) feed on the foliage, as do the caterpillars of several moths, including Holomelina aurantiaca (Orange Holomelina), Hymenia perspectalis (Spotted Beet Webworm Moth), Spilosoma congrua (Agreeable Tiger Moth), and Spoladea recurvalis (Hawaiian Beet Webworm Moth). Sometimes Disonycha spp. (Flea Beetles) chew little holes in the leaves. The seeds of pigweeds are very popular with granivorus birds as a source of food during the fall and winter (see Bird Table). Pigs and cattle eat pigweeds readily, although the foliage can cause bloating and other symptoms of nitrate poisoning if an excessive amount of the foliage is eatened. Deer and rabbits eat pigweeds to a limited extent.

Insects rarely visit the wind-pollinated flowers. The caterpillars of the skipper Pholisora catullus (Common Sootywing) feed on the foliage, as do the caterpillars of several moths, including Holomelina aurantiaca (Orange Holomelina), Hymenia perspectalis (Spotted Beet Webworm Moth), Spilosoma congrua (Agreeable Tiger Moth), and Spoladea recurvalis (Hawaiian Beet Webworm Moth). Sometimes Disonycha spp. (Flea Beetles) chew little holes in the leaves. The seeds of pigweeds are very popular with granivorus birds as a source of food during the fall and winter (see Bird Table). Pigs and cattle eat pigweeds readily, although the foliage can cause bloating and other symptoms of nitrate poisoning if an excessive amount of the foliage is eatened. Deer and rabbits eat pigweeds to a limited extent.

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Species: 2
Species With Barcodes: 1

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 7
Species: 16
Species With Barcodes: 1

Rounded Global Status Rank: TNR - Not Yet Ranked

Rounded Global Status Rank: G5 - Secure

Canada

Rounded National Status Rank: NNA - Not Applicable

Canada

Rounded National Status Rank: NNA - Not Applicable

United States

Rounded National Status Rank: NNR - Unranked

Comments: A black-seeded African diploid species, the probable wild form of A. hypochondriacus.

This plant typically occurs in full sun, mesic to dry conditions, and a soil containing loam, clay-loam, or gravel. The size of individual plants is highly variable, depending on soil fertility and moisture amounts.

This plant typically occurs in full sun, mesic conditions, and a loamy soil with high nitrogen content. However, it is adaptable and can be found in gravelly soil, clay-loam, and moist to dry areas. The size of individual plants is highly variable, depending on soil fertility and moisture amounts. The seeds can remain viable in the soil for eat least 30 years.