Amaranthus hybridus
Amaranthus torreyi
green amaranth, green pigweed, hybrid amaranth, slender pigweed, slim amaranth, smooth amaranth, smooth pigweed
Bigelow's amaranth, sandhill amaranth, Torrey's amaranth, Torrey's amaranthus
erect, green or sometimes reddish purple, rarely under-developed plants ascending, branched to nearly simple, 0.3–2(–2.5) m.
erect or ascending proximally, much-branched especially near base, 0.1–0.7 m.
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 less than 1/2 as long as blade;
blade oblanceolate or lanceolate to ovate-lanceolate, (1.2–)1.5–5(–7) × 0.3–2 cm, base narrowly cuneate to cuneate, margins entire, plane or slightly undulate, apex acute to subobtuse, mucronulate.
lanceolate-linear to subulate, 2–3.5(–4) mm, subequal to or 2 times as long as tepals, apex spinescent.
lanceolate to linear-subulate, 1.3–3.5 mm, slightly longer than tepals.
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 clusters, toward apex aggregated in spikes (rarely spicate panicles), axes, leafy (occasionally almost leafless distally).
at tips of inflorescences;
tepals 5;
stamens (4–)5.
mostly at tips of inflorescences;
tepals 5, equal or subequal;
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 5, spatulate to narrowly spatulate, clawed, equal or subequal, 1.5–2.5 mm, margins entire, apex obtuse, rounded, or slightly emarginate;
style branches erect;
stigmas 3.
black to dark reddish brown, lenticular to lenticular-globose, 1–1.3 mm, smooth, shiny.
black, subglobose to broadly lenticular, 1 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.
obovoid to subglobose-obovoid, 1.5–2 mm, nearly equaling or slightly shorter than tepals, smooth, dehiscence regularly circumscissile.
Amaranthus hybridus
Amaranthus torreyi
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 torreyi has been widely misapplied to at least two other species, 7. A. arenicola and 6. A. watsonii. Because of that, the name A. bigelovii was used for A. torreyi by J. D. Sauer (1955) and in some recent floras. Sometimes A. torreyi (California and Arizona) and A. bigelovii (New Mexico and Texas) are recognized as separate species. The nomenclature and taxonomic relationships in this group should be critically reviewed based on type specimens and additional experimental and field studies.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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