Flora of North America species comparison

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Amaranthus hybridus

Amaranthaceae

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

amaranth family
Habit Plants glabrous or glabrescent, or distal parts of stem and branches slightly pubescent when young. Herbs, rarely subshrubs, annual or perennial; trichomes simple (branched in Tidestromia).
Stems

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

without nodal spines (Amaranthus spinosus sometimes with paired nodal spines).
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.

alternate or opposite, exstipulate, usually petiolate;

blade margins entire (entire or serrulate in Iresine; entire, crispate, or erose in Amaranthus).
Bracts

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

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.

cymules arranged in spikes, panicles, thyrses, heads, glomerules, clusters, or racemes; each flower subtended by 1 bract and 2 bracteoles (latter sometimes 1 or absent in Amaranthus).
Flowers

bisexual or unisexual (plants then monoecious or dioecious), hypogynous, generally small or minute;

tepals mostly (1–)4–5 or absent, distinct or connate into cups or tubes, scarious, chartaceous, membranaceous, or indurate;

stamens 2–5, filaments basally connate into cups or tubes, rarely distinct, alternating with pseudostaminodes (appendages on staminal tubes) or not, anthers 2-locular with 1 line of dehiscence or 4-locular with 2 lines of dehiscence;

ovary superior, 1-locular;

ovules 1 or, rarely, 2–many;

style 1 or absent;

stigmas 1–3(–5).
Staminate flowers

at tips of inflorescences;

tepals 5;

stamens (4–)5.

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.

Fruits

utricles, dry, dehiscent or not.
Seeds

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

black, reddish brown, or brown, lenticular, subglobose or globose (rarely cylindric), usually small;

embryo peripheral, surrounding mealy perisperm.
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.

Amaranthus hybridus

Amaranthaceae
Phenology Flowering summer–fall.
Habitat Waste places, agricultural and fallow fields, railroads, roadsides, riverbanks, other disturbed habitats
Elevation 0-2500 m (0-8200 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]
Nearly worldwide; most abundant in tropics; subtropics; and warm-temperate regions; evidently absent from alpine and arctic regions
[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.)

Genera ca. 65, species ca. 900 (12 genera, 80 species in the flora).

Centers of diversity for Amaranthaceae are southwestern North America, Central America, South America, and Africa south of the Sahara Desert. Generic limits are not well defined in some groups; fewer than 60 or more than 70 genera could be recognized.

Some species occur in severe habitats such as sandy, calcareous, gypseous, saline, or serpentine soils in deserts, semideserts, and seashores. Some species are weedy, including the major agricultural weeds in Amaranthus. Some species are cultivated as ornamentals, particularly Amaranthus caudatus (love-lies-bleeding), A. hypochondriacus (prince’s-feather), A. tricolor (Joseph’s-coat), Celosia cristata (cockscomb), and Gomphrena globosa (globe-amaranth). Native Americans domesticated white-seeded grain amaranths (A. caudatus, A. cruentus, and A. hypochondriacus) for use as cereal grains. Some species of Amaranthus and Celosia are potherbs.

Amaranthaceae are usually divided into subfamilies Amaranthoideae (anthers 4-locular with two lines of dehiscence) and Gomphrenoideae Schinz (anthers 2-locular with one line of dehiscence). Amaranthaceae and Chenopodiaceae have long been recognized as allied families that share a number of features: generally small flowers, one perianth whorl, a syncarpous gynoecium with a superior ovary and often only one ovule, basal or free-central placentation, pollen characteristics, centrospermous embryo development, betalain pigments, and P-type form (c) sieve-element plastids.

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Key
1. Distal leaves alternate
→ 2
1. Distal leaves opposite
→ 5
2. Flowers unisexual (plants monoecious or dioecious); utricles 1-seeded
→ 3
2. Flowers bisexual; utricles 2+-seeded
→ 4
3. Shrubs
Iresine
3. Herbs, annual, rarely perennial
Amaranthus
4. Leaf blades mostly lanceolate, ovate, or deltate; pseudostaminodes absent
Celosia
4. Leaf blades linear; pseudostaminodes alternating with filaments on staminal tubes
Hermbstaedtia
5. Flowers unisexual (plants dioecious); inflorescences terminal, diffuse, open panicles
Iresine
5. Flowers bisexual; inflorescences terminal and/or axillary glomerules, heads, or spikes
→ 6
6. Inflorescences sessile glomerules or condensed spikes, axillary
→ 7
6. Inflorescences pedunculate heads or spikes, terminal and sometimes axillary near stem tips
→ 10
7. Inflorescences several-flowered, axillary spikes; pseudostaminodes present
Alternanthera
7. Inflorescences 1-20-flowered, axillary glomerules; pseudostaminodes present or absent
→ 8
8. Indumentum of branched or barbed trichomes, densely covering plant (rarely glabrous); pseudostaminoides present
Tidestromia
8. Indumentum of simple trichomes; pseudostaminoides absent
→ 9
9. Tepals connate proximally, tips 1-veined; filament tubes inserted distally on perianth tubes; basal rosette leaves usually absent at anthesis
Guilleminea
9. Tepals distinct, 3-veined; filament tubes ± free from tepals; basal rosette leaves present at anthesis
Gossypianthus
10. Inflorescences simple or compound spikes
→ 11
10. Inflorescences globose or cylindric heads or spikes
→ 12
11. Inflorescences mostly compound, interrupted spikes; tepals connate into indurate tubes with lateral crests or spines, lanate
Froelichia
11. Inflorescences simple spikes or few-branched panicles, flowers progressively farther apart below; tepals basally connate into indurate tubes, without ornamentation, ± glabrous
Achyranthes
12. Inflorescences not immediately subtended by leaves
Alternanthera
12. Inflorescences immediately subtended by 2 or more leaves
→ 13
13. Leaves fleshy, sessile; blade linear to narrowly obovate, glabrous except in axils
Blutaparon
13. Leaves not fleshy, petiolate or sessile; blade ovate to obovate, pilose at least abaxially
Gomphrena
Source FNA vol. 4. FNA vol. 4, p. 405. Authors: Kenneth R. Robertson, Steven E. Clemants.
Parent taxa Amaranthaceae > Amaranthus > subg. Amaranthus
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
Subordinate taxa
Achyranthes, Alternanthera, Amaranthus, Blutaparon, Celosia, Froelichia, Gomphrena, Gossypianthus, Guilleminea, Hermbstaedtia, Iresine, Tidestromia
Name authority Linnaeus: Sp. Pl. 2: 990. (1753) Jussieu
Web links 
Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



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