Amaranthus retroflexus
Amaranthus scleropoides
common amaranth, pigweed amaranth, red-root amaranth, red-root pigweed, rough pigweed, wild-beet amaranth
bonebract amaranth, bonebract pigweed
erect, reddish near base, branched in distal part to simple 0.2–1.5(–2) m; underdeveloped or damaged plants rarely ascending to nearly prostrate.
ascending to prostrate, erect when young, or main stems ± erect, branched proximally, 0.1–0.6 m. Leaves: petiole equaling or 1/2 as long as blade;
blade elliptic, oblanceolate to lanceolate, (0.5–)1–3(–3.5) × 0.3–2 cm, base tapering, margins entire, plane to slightly undulate, apex broadly rounded or emarginate.
petiole 1/2 to equaling blade;
blade ovate to rhombic-ovate, 2–15 × 1–7 cm, base cuneate to rounded-cuneate, margins entire, plane or slightly undulate, apex acute, obtuse, or slightly emarginate, with terminal mucro.
lanceolate to subulate, (2.5–)3.5–5(–6) mm, exceeding tepals, apex acuminate with excurrent midrib.
of pistillate flowers keeled (only A. scleropoides and A. crassipes have keeled bracts), ovate-triangular, minute.
terminal and axillary, erect or reflexed at tip, green or silvery green, often with reddish or yellowish tint, branched, leafless at least distally, usually short and thick.
axillary clusters borne from base to top, axes thickened and inflated, becoming indurate at maturity (only in A. scleropoides and A. crassipes).
few at tips of inflorescences;
tepals 5;
stamens (3–)4–5.
intermixed with pistillate;
tepals 5, membranaceous;
stamens 3.
tepals 5, spatulate-obovate, lanceolate-spatulate, not clawed, subequal or unequal, (2–)2.5–3.5(–4) mm, membranaceous, apex emarginate or obtuse, with mucro;
style branches erect or slightly spreading,;
stigmas 3.
tepals 5, narrowly spatulate, slightly clawed, with expanded blade, equal or subequal, (1.2–)1.5–2.5 mm, apex acute to apiculate;
claws indurate at maturity;
style branches spreading;
stigmas 2–3.
black to dark reddish brown, lenticular to subglobose-lenticular, 1–1.3 mm, smooth, shiny.
dark brownish black to black, compressed-ovoid to broadly lenticular, 0.9–1.1 mm diam., shiny.
broadly obovoid to broadly elliptic, 1.5–2.5 mm, shorter than or subequal to tepals, smooth or slightly rugose, especially near base and in distal part, dehiscence regularly circumscissile.
orbicular to compressed-obovoid, 1.1–1.5 mm, shorter than tepals, smooth to tuberculate in distal 1/2, dehiscence regularly circumscissile.
Amaranthus retroflexus
Amaranthus scleropoides
Amaranthus retroflexus, native to central and eastern North America, is a successful invasive species and has effectively colonized a wide range of habitats on all inhabited continents. Its variability is extremely wide; usually the species is easily recognized and its identification causes no specific problems. Infraspecific entities described within A. retroflexus are mostly ecologic variants of little or no taxonomic value. Two varieties are more easily recognized: the common var. retroflexus, with bracts about 1.5–2 times as long as tepals, and a more rare var. delilei (Richter & Loret) Thellung (= A. delilei Richter & Loret), with bracts 1–1.5 times as long as tepals.
Occasional forms morphologically intermediate between Amaranthus retroflexus and taxa of the A. hybridus aggregate (e.g., A. powellii and A. hybridus, in the strict sense) are known both in the Americas and the Old World. Usually such plants are treated as hybrids; in many cases they are probably just extremes of the natural variability of A. retroflexus. Putative hybrids of A. retroflexus were described from Europe as A. ×ozanonii Thellung (A. hybridus × A. retroflexus) and A. ×soproniensis Priszter & Karpáti (A. powellii × A. retroflexus) (see A. Thellung 1914–1919; S. Priszter 1958; P. Aellen 1959; F. Grüll and S. Priszter 1973).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
A hybrid between Amaranthus crassipes and A. scleropoides was recently described as A. ×texensis Henrickson and reported from southeastern Texas (J. Henrickson 1999).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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