Amaranthus muricatus
Amaranthus hybridus
African amaranth, muricate amaranth
green amaranth, green pigweed, hybrid amaranth, slender pigweed, slim amaranth, smooth amaranth, smooth pigweed
ascending or prostrate, much-branched from stout rootstock, 0.1–0.4 m.
erect, green or sometimes reddish purple, rarely under-developed plants ascending, branched to nearly simple, 0.3–2(–2.5) m.
petiole to 1/2 as long as blade;
blade linear to narrowly lanceolate, 1.5–8 × 0.2–0.5(–1) mm, base tapering, margins entire, plane to undulate, apex obtuse and often emarginate.
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.
of pistillate flowers linear, 0.7–1.2 mm, 1/2–2/3 as long as tepals.
lanceolate-linear to subulate, 2–3.5(–4) mm, subequal to or 2 times as long as tepals, apex spinescent.
terminal, compact pyramidal panicles and axillary glomerules, erect or reflexed, green, leafless at least distally.
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.
intermixed with pistillate or at tips of inflorescences;
tepals 5;
stamens 5.
at tips of inflorescences;
tepals 5;
stamens (4–)5.
tepals 5, narrowly oblanceolate, not clawed, equal, 1.5–2 mm, apex obtuse or subacute;
style branches erect;
stigmas 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.
black, lenticular, 1–1.2 mm diam., semiglossy.
black to dark reddish brown, lenticular to lenticular-globose, 1–1.3 mm, smooth, shiny.
compressed, subglobose, 1.7–2 mm, ± equaling or slightly exceeding tepals, muricate, indehiscent.
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 muricatus
Amaranthus hybridus
The vernacular name “African amaranth” is sometimes used for this species; it is a misnomer; the species is native to South America and naturalized in Africa.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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.)
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