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

green amaranth, slender amaranth, tropical green amaranth

Habit Plants glabrous or glabrescent, or distal parts of stem and branches slightly pubescent when young. Plants annual, sometimes short-lived perennial in tropics and subtropics, glabrous.
Stems

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

erect, simple or with lateral branches (especially distally), 0.2–1 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 1/2–11/2 as long as blade;

blade rhombic-ovate or ovate, 1–7 × 0.5–5 cm, base rounded, cuneate, or attenuate, margins entire, plane, apex obtuse, rounded, or emarginate, mucronate.

Bracts

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

of pistillate flowers ovate to lanceolate, 1 mm, shorter than 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.

slender spikes aggregated into elongate terminal panicles, also from distal axils, green, leafless at least distally.

Staminate flowers

at tips of inflorescences;

tepals 5;

stamens (4–)5.

inconspicuous, mostly at tips of inflorescences;

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 elliptic, obovate-elliptic or spatulate, not clawed, ± equal, 1.2–1.7 mm, apex rounded or nearly acute, mucronate or not;

style branches erect;

stigmas 3.

Seeds

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

black or dark brown, subglobose to thick-lenticular, 1 mm diam., minutely punctulate, rather dull.

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.

ovoid to compressed-ovoid, 1–1.6 mm, equaling or slightly exceeding tepals, prominently or faintly rugose, indehiscent.

Amaranthus hybridus

Amaranthus viridis

Phenology Flowering summer–fall. Flowering summer–fall.
Habitat Waste places, agricultural and fallow fields, railroads, roadsides, riverbanks, other disturbed habitats Fields, railroads, lawns, gardens, waste areas, other disturbed habitats
Elevation 0-2500 m (0-8200 ft) 0-1000 m (0-3300 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
AL; AR; AZ; FL; GA; LA; MA; MI; MS; NC; NM; NY; OK; PA; SC; TN; TX; VA; native to South America [Introduced in North America; introduced in tropical and subtropical regions worldwide]
[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.)

Source FNA vol. 4. FNA vol. 4, p. 429.
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. 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. 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. viscidulus, A. watsonii, A. wrightii
Synonyms A. gracilis
Name authority Linnaeus: Sp. Pl. 2: 990. (1753) Linnaeus: Sp. Pl. ed. 2, 2: 1405. (1763)
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