Amaranthus retroflexus
Amaranthus albus
common amaranth, pigweed amaranth, red-root amaranth, red-root pigweed, rough pigweed, wild-beet amaranth
pigweed amaranth, prostrate pigweed, tumble pigweed, tumbleweed, tumbleweed amaranth, tumbling pigweed, white amaranth, white 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.
usually erect, ascending proximally, rarely almost prostrate, much-branched, bushy (large plants forming tumbleweeds), 0.1–1 m. Leaves: petiole 1/2 as long as blade, or longer in young proximal leaves;
blade obovate to narrowly spatulate, mostly 0.5 × 0.5–1.5 cm, early proximal leaves to 8 cm, base tapering, narrowly cuneate, margins entire, plane (or ± distinctly undulate), apex obtuse, with whitish or yellowish, subspinescent mucro.
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 subulate to linear-lanceolate, narrow, 2–3 mm, 2 times as long as tepals.
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 glomerules, green, whitish green, or yellowish.
few at tips of inflorescences;
tepals 5;
stamens (3–)4–5.
intermixed with pistillate;
tepals 3;
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 3, narrowly ovate to linear, slightly unequal, 1–1.5 mm, thin, apex acute;
style branches erect;
stigmas 3.
black to dark reddish brown, lenticular to subglobose-lenticular, 1–1.3 mm, smooth, shiny.
dark reddish brown to black, lenticular, 0.6–1 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.
ellipsoid-ovoid, 1.5 mm, equaling or exceeding tepals, smooth proximally, coarsely rugose distally, dehiscence regularly circumscissile.
Amaranthus retroflexus
Amaranthus albus
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.)
The name Amaranthus graecizans, which refers to a species of Old World origin, has been misapplied to both A. albus and A. blitoides in earlier North American floras and manuals.
Southwestern plants differing from typical Amaranthus albus in having viscid pubescence and usually distinctly crisped leaf margins may be recognized as var. pubescens; they were occasionally treated as a separate species, A. pubescens.
Amaranthus albus and A. blitoides are rather often confused in herbaria. The species are easily distinguished by their seed size and luster.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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WildflowerSearch
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- Local floras: BC, CA, OR, WA
- Local Web sites: CalFlora, CalPhotos, Flora NW, Go Botany, IL Wildflowers, KS Wildflowers, LA Plants, MD Biodiversity, MI Flora, MN Wildflowers, MO Plants, PNW Herbaria
- WildflowerSearch
- iNaturalist (observations)
- USDA Plants Database
- LBJ Wildflower Center
- SEINet
- Plants of the World Online
- Encyclopedia of Life
- Wikipedia
- Google Image Search
