Amaranthus hybridus
Amaranthus powellii
green amaranth, green pigweed, hybrid amaranth, slender pigweed, slim amaranth, smooth amaranth, smooth pigweed
green amaranth, green pigweed, Powell's amaranth, Powell's smooth amaranth
erect, green or sometimes reddish purple, rarely under-developed plants ascending, branched to nearly simple, 0.3–2(–2.5) m.
usually erect, green or sometimes reddish purple, branched, mainly in inflorescences, to nearly simple, 0.3–1.5(–2) m, stiff.
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 mostly equaling or longer than blade;
blade rhombic-ovate to broadly lanceolate, 4–8 × 2–3 cm, occasionally larger in robust plants, base cuneate to broadly cuneate, margins entire, apex cuneate to obtuse or indistinctly emarginate, with mucro.
lanceolate-linear to subulate, 2–3.5(–4) mm, subequal to or 2 times as long as tepals, apex spinescent.
lanceolate to linear-subulate, 4–7 mm, 2–3 times as long as tepals, rigid.
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.
mostly terminal, usually with spikes at distal axils, erect and rigid, green to silvery green, occasionally tinged red, leafless at least distally.
at tips of inflorescences;
tepals 5;
stamens (4–)5.
clustered at tips of inflorescence branches;
tepals 3–5;
stamens 3–5.
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 usually 3–5, not clawed, unequal;
outer tepals narrowly ovate-elliptic or elliptic, 1.5–3.5 mm, apex aristate;
style branches spreading, shorter than body of fruit;
stigmas 3.
black to dark reddish brown, lenticular to lenticular-globose, 1–1.3 mm, smooth, shiny.
black, subglobose to lenticular, 1–1.4 mm diam., smooth, shiny.
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.
subglobose or compressed-ovoid, 2–3 mm, equaling or shorter than tepals, smooth or lid slightly rugose or minutely verrucose, dehiscence regularly circumscissile.
Amaranthus hybridus
Amaranthus powellii
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.)
Amaranthus powellii is originally native to southwestern United States and adjacent regions of Mexico; now, it is widely naturalized almost everywhere in temperate regions of North America. The distribution of A. powellii is probably underestimated both in North America and the Old World, and literature references are somewhat confusing, because A. powellii has been commonly confused with A. hybridus.
Forms of Amaranthus powellii with indehiscent or occasionally irregularly dehiscent utricles were described from Europe (southwestern France, the Gironde estuary) as A. bouchonii Thellung. Similar forms occasionally occur in North America. According to J. M. Tucker and J. D. Sauer (1958) and J. D. Sauer (1967b, 1972b), they are mostly “mutant or aberrant forms” of A. powellii, or hybrids of A. powellii and/or A. hybridus with other species. Recent comparative studies of morphology and isozymes of A. bouchonii (P. Wilkin 1992) indicated that that taxon, whatever its origin was, now differs from its presumably parental species and probably deserves recognition, at least as a separate subspecies. It seems that in North America, the situation with indehiscent-fruited forms is much more complicated than in Europe, and multiple entities are involved, including deviate forms of A. powellii and also partly sterile hybrids of dioecious taxa with species belonging to the A. hybridus group. The formal recognition of A. bouchonii in North American material would be premature.
The names Amaranthus hybridus, A. chlorostachys Willdenow, and A. hybridus subsp. chlorostachys (Willdenow) Hejný were occasionally misapplied to A. powellii in North America and Europe.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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