Amaranthus hybridus
Amaranthus crassipes
green amaranth, green pigweed, hybrid amaranth, slender pigweed, slim amaranth, smooth amaranth, smooth pigweed
clubfoot amaranth, spreading amaranth, tropical spreading amaranth
erect, green or sometimes reddish purple, rarely under-developed plants ascending, branched to nearly simple, 0.3–2(–2.5) m.
prostrate or weakly ascending, erect when young, branched mostly from base, 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 nearly 1/2 as long as blade;
blade broadly elliptic, obovate, orbiculate, or oblanceolate, (0.5–)1–3(–4.5) × 0.3–2(–2.5) cm, base cuneate, margins entire, plane to undulate, apex broadly rounded or emarginate.
lanceolate-linear to subulate, 2–3.5(–4) mm, subequal to or 2 times as long as tepals, apex spinescent.
of pistillate flowers keeled (only A. scleropoides and A. crassipes have keeled bracts), deltate, 0.5–0.9 mm.
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 borne from base to apex, axes much thickened, appearing inflated, becoming indurate at maturity (only in A. scleropoides and A. crassipes).
at tips of inflorescences;
tepals 5;
stamens (4–)5.
intermixed with pistillate;
tepals 5, membranaceous;
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 (4–)5, narrowly spatulate, clawed, with small expanded blade, equal or subequal, 2–3 mm, apex rounded and apiculate;
claws becoming indurate and scarious at maturity;
style branches spreading;
stigmas usually 2(–3), almost sessile.
black to dark reddish brown, lenticular to lenticular-globose, 1–1.3 mm, smooth, shiny.
dark brownish or reddish black to black, compressed-ovoid to broadly lenticular, 1–1.4 mm diam., 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 compressed-obovoid, 1.4–2 mm, shorter than tepals, prominently muricate (especially in distal 1/2), indehiscent.
Amaranthus hybridus
Amaranthus crassipes
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.)
Two varieties have been distinguished by J. Henrickson (1999) within Amaranthus crassipes: var. crassipes with leaf blades nearly orbiculate to ovate (obovate) and conspicuous veins on the green to yellow-green abaxial leaf surface; and var. warnockii (I. M. Johnston) Henrickson (= A. warnockii I. M. Johnston) with narrower oblanceolate grayish leaves with less distinct venation on the abaxial leaf surfaces. In Henrickson’s treatment, var. crassipes occurs mostly in the coastal areas (and is also reported for Arizona), while var. warnockii is reported from inland southwestern Texas and the Chihuahuan Desert region (Mexico: Coahuila, Chihuahua). We have not seen material of the new varieties and cannot evaluate their validity.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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