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green amaranth, green pigweed, hybrid amaranth, slender pigweed, slim amaranth, smooth amaranth, smooth pigweed

pigweed amaranth, prostrate pigweed, tumble pigweed, tumbleweed, tumbleweed amaranth, tumbling pigweed, white amaranth, white pigweed

Habit Plants glabrous or glabrescent, or distal parts of stem and branches slightly pubescent when young. Plants annual, glabrous or glabrescent or viscid-pubescent.
Stems

erect, green or sometimes reddish purple, rarely under-developed plants ascending, branched to nearly simple, 0.3–2(–2.5) m.

usually erect, ascending proximally, rarely almost prostrate, much-branched, bushy (large plants forming tumbleweeds), 0.1–1 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.

petiole 1/2 as long as blade, or longer in young proximal leaves;

blade obovate to narrowly spatulate, mostly 0.5 × 0.5–1.5 cm, early proximal leaves to 8 cm, base tapering, narrowly cuneate, margins entire, plane (or ± distinctly undulate), apex obtuse, with whitish or yellowish, subspinescent mucro.

Bracts

lanceolate-linear to subulate, 2–3.5(–4) mm, subequal to or 2 times as long as tepals, apex spinescent.

of pistillate flowers subulate to linear-lanceolate, narrow, 2–3 mm, 2 times as long as tepals.

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.

axillary glomerules, green, whitish green, or yellowish.

Staminate flowers

at tips of inflorescences;

tepals 5;

stamens (4–)5.

intermixed with pistillate;

tepals 3;

stamens 3.

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.

tepals 3, narrowly ovate to linear, slightly unequal, 1–1.5 mm, thin, apex acute;

style branches erect;

stigmas 3.

Seeds

black to dark reddish brown, lenticular to lenticular-globose, 1–1.3 mm, smooth, shiny.

dark reddish brown to black, lenticular, 0.6–1 mm diam., shiny.

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.

ellipsoid-ovoid, 1.5 mm, equaling or exceeding tepals, smooth proximally, coarsely rugose distally, dehiscence regularly circumscissile.

Amaranthus hybridus

Amaranthus albus

Phenology Flowering summer–fall. Flowering summer–fall.
Habitat Waste places, agricultural and fallow fields, railroads, roadsides, riverbanks, other disturbed habitats Disturbed habitats, waste places, vacant areas, railroads, streambanks, sandy areas, roadsides, agricultural fields
Elevation 0-2500 m (0-8200 ft) 0-2200 m (0-7200 ft)
Distribution
from FNA
AL; AR; AZ; CA; CO; CT; DC; DE; FL; GA; IA; ID; IL; IN; KS; KY; LA; MA; MD; ME; MI; MN; MO; MS; MT; NC; ND; NE; NH; NJ; NM; NV; NY; OH; OK; PA; RI; SC; SD; TN; TX; VA; VT; WA; WI; WV; BC; MB; NS; ON; QC; Mexico; Central America; South America; West Indies [Widely introduced or naturalized in tropical, subtropical, and warm-temperate regions worldwide]
[WildflowerSearch map]
[BONAP county map]
from FNA
AK; AL; AR; AZ; CA; CO; CT; DC; DE; FL; GA; IA; ID; IL; IN; KS; KY; LA; MA; MD; ME; MI; MN; MO; MS; MT; NC; ND; NE; NH; NJ; NM; NV; NY; OH; OK; OR; PA; RI; SC; SD; TN; TX; UT; VA; VT; WA; WI; WV; WY; AB; BC; MB; NB; NL; NS; ON; PE; QC; SK; SPM; Mexico [Introduced in North America; introduced and often successfully naturalized in South America, Eurasia, Africa, Australia]
[WildflowerSearch map]
[BONAP county map]
Discussion

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.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

The name Amaranthus graecizans, which refers to a species of Old World origin, has been misapplied to both A. albus and A. blitoides in earlier North American floras and manuals.

Southwestern plants differing from typical Amaranthus albus in having viscid pubescence and usually distinctly crisped leaf margins may be recognized as var. pubescens; they were occasionally treated as a separate species, A. pubescens.

Amaranthus albus and A. blitoides are rather often confused in herbaria. The species are easily distinguished by their seed size and luster.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Source FNA vol. 4. FNA vol. 4.
Parent taxa Amaranthaceae > Amaranthus > subg. Amaranthus Amaranthaceae > Amaranthus > subg. Albersia
Sibling taxa
A. acanthochiton, A. albus, A. arenicola, A. australis, A. blitoides, A. blitum, A. californicus, A. cannabinus, A. caudatus, A. crassipes, A. crispus, A. cruentus, A. deflexus, A. dubius, A. fimbriatus, A. floridanus, A. graecizans, A. greggii, A. hypochondriacus, A. muricatus, A. obcordatus, A. palmeri, A. polygonoides, A. powellii, A. pumilus, A. retroflexus, A. scleropoides, A. spinosus, A. tamaulipensis, A. thunbergii, A. torreyi, A. tricolor, A. tuberculatus, A. viridis, A. viscidulus, A. watsonii, A. wrightii
A. acanthochiton, A. arenicola, A. australis, A. blitoides, A. blitum, A. californicus, A. cannabinus, A. caudatus, A. crassipes, A. crispus, A. cruentus, A. deflexus, A. dubius, A. fimbriatus, A. floridanus, A. graecizans, A. greggii, A. hybridus, A. hypochondriacus, A. muricatus, A. obcordatus, A. palmeri, A. polygonoides, A. powellii, A. pumilus, A. retroflexus, A. scleropoides, A. spinosus, A. tamaulipensis, A. thunbergii, A. torreyi, A. tricolor, A. tuberculatus, A. viridis, A. viscidulus, A. watsonii, A. wrightii
Synonyms A. albus var. pubescens, A. pubescens
Name authority Linnaeus: Sp. Pl. 2: 990. (1753) Linnaeus: Syst. Nat. ed. 10, 2: 1268. (1759)
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