Amaranthus hybridus
Amaranthus blitum
green amaranth, green pigweed, hybrid amaranth, slender pigweed, slim amaranth, smooth amaranth, smooth pigweed
Guernsey pigweed, livid amaranth, pale amaranth, purple amaranth
erect, green or sometimes reddish purple, rarely under-developed plants ascending, branched to nearly simple, 0.3–2(–2.5) m.
ascending to prostrate, sometimes erect, simple or branched, sometimes radiating from base and forming mats, 0.1–0.6 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 usually equaling to 2 times as long as blade;
blade ovate or obovate, 1–6 × 0.5–4 cm, base tapering or cuneate, margins entire, plane, apex distinctly emarginate to almost bilobate, mucronate.
lanceolate-linear to subulate, 2–3.5(–4) mm, subequal to or 2 times as long as tepals, apex spinescent.
of pistillate flowers lanceolate, inconspicuous, 0.5 mm, shorter 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.
slender terminal spikes or panicles and also axillary clusters, in some forms only axillary clusters are present;
spikes erect or sometimes reflexed, green, leafless at least distally.
at tips of inflorescences;
tepals 5;
stamens (4–)5.
clustered at tips of spikes;
tepals 3;
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 3, elliptic or spatulate, not clawed, equal or subequal, 0.8–1.5 mm, margins entire, apex broadly acute;
style branches erect;
stigmas 3.
black to dark reddish brown, lenticular to lenticular-globose, 1–1.3 mm, smooth, shiny.
black or dark reddish brown, subglobose or broadly lenticular, (0.8–)1–1.8 mm diam., smooth, shiny, filling fruit almost completely.
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.
compressed, subglobose to obovate, 1.2–2.5(–3) mm, exceeding tepals, smooth or faintly rugose, indehiscent.
Amaranthus hybridus
Amaranthus blitum
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 lividus has been widely used for A. blitum, in addition to other Linnaean names (see F. Fillias et al. 1980; J. P. M. Brenan and C. C. Townsend 1980; R. K. Brummitt 1984). Amaranthus blitum is of tropical origin and not common in temperate regions. It has been cultivated in Europe as a minor leaf-vegetable crop, but now it is declining and its range is becoming progressively smaller. In many temperate countries (in particular in Europe), A. blitum persists mostly as an uncommon and sporadic weed in greenhouses, ornamental gardens, and flower beds.
In Europe, it may be possible to distinguish two or three subspecies within Amaranthus blitum. The occurrence and distribution of infraspecific taxa of the A. blitum complex is insufficiently known in North America and requires additional floristic and taxonomic studies, although it appears that the most common is subsp. polygonoides (Moquin-Tandon) Cattetero. Some literature records of A. blitum from southern regions of North America are misidentifications of A. viridis, and vice versa; because of that the distributions of these two species in the flora area require critical reassessment.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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