Amaranthus hybridus
Amaranthus obcordatus
green amaranth, green pigweed, hybrid amaranth, slender pigweed, slim amaranth, smooth amaranth, smooth pigweed
trans-Pecos amaranth
erect, green or sometimes reddish purple, rarely under-developed plants ascending, branched to nearly simple, 0.3–2(–2.5) m.
erect or ascending, branched, 0.1–0.5 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 1/2 as long as blade;
blade oblong-lanceolate to lanceolate-linear, 1–3 × 0.2–1 cm, base cuneate to narrowly cuneate, margins entire, plane or sometimes undulate, apex rounded or obtuse-truncate, mucronate.
lanceolate-linear to subulate, 2–3.5(–4) mm, subequal to or 2 times as long as tepals, apex spinescent.
broadly ovate, 1 mm or shorter, 1/2 or less length of tepals, apex acute.
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 axillary, but at apex flowers also condensed in terminal spikes or spicate panicles, usually leafy proximally or nearly leafless distally.
at tips of inflorescences;
tepals 5;
stamens (4–)5.
tepals (3–)5;
stamens 3.
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, spreading at maturity, spatulate, clawed, subequal, 2 mm, margins fimbriate, apex rounded or shallowly emarginate;
stigmas 3.
black to dark reddish brown, lenticular to lenticular-globose, 1–1.3 mm, smooth, shiny.
dark reddish brown to nearly black, lenticular or broadly lenticular, 0.6–0.8 mm diam., smooth.
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.
narrowly oblong, 1–1.4 mm, shorter than tepals, indehiscent.
Amaranthus hybridus
Amaranthus obcordatus
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 obcordatus has been reported only from southern Arizona (T. H. Kearney and R. H. Peebles 1960), trans-Pecos Texas in Brewster and Pecos counties, and adjacent regions of Mexico (C. F. Reed 1969b). It was also tentatively reported for New Mexico, but no localities were cited (W. C. Martin and C. R. Hutchins 1980). The proper taxonomic position of A. obcordatus and its relationships to other species remain problematic and are in need of further study.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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