Amaranthus retroflexus L.
  • Sp. Pl.
  • Redroot pigweed, redroot amaranth, wild-beet amaranth, rough pigweed, common amaranth


This taxon is accepted by Amaranthaceae
Notes: More details could be found in The Plant List v.1.1. Originally in The Plant List v.1.0

General Information

Stem erect, light green, 20-80 cm tall, stout, branched or not, slightly obtusely angulate, densely pubescent. Petiole light green, 1.5-5.5 cm, hairy; leaf blade ovate-rhombic or elliptic, 5-12 × 2-5 cm, both surfaces shortly hairy, but densely hairy abaxially, base cuneate, margin entire and undulate, apex acute or notched, with a mucro. Complex thyrsoid structures terminal and axillary, erect, 2-4 cm in diam., including many spikes; terminal spikes longer than lateral ones. Bracts and bracteoles white, subulate, 4-6 mm, apex slenderly long pointed. Tepals white, oblong or oblong-obovate, 2-2.5 mm, membranous, with a green midvein, apex acute or notched, with a mucro. Stamens slightly longer than perianth. Stigmas 3, rarely 2. Utricles light green, ovoid, compressed, shorter than perianth, circumscissile. Seeds brown or black, subglobose, ca. 1 mm in diam., obtuse at margin. Fl. Jul-Aug, fr. Aug-Sep. 2n = 32*, 34*, 102*.

  • Provided by: [D].Flora Of CHina @ efloras.org
    • Source: [
    • 3
    • ]. 

    Plants densely to moderately pubescent, especially distal parts of stem and branches. Stems 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. Leaves: 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. Inflorescences 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. Bracts lanceolate to subulate, (2.5-)3.5-5(-6) mm, exceeding tepals, apex acuminate with excurrent midrib. Pistillate flowers: 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. Staminate flowers few at tips of inflorescences; tepals 5; stamens (3-)4-5. Utricles 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. Seeds black to dark reddish brown, lenticular to subglobose-lenticular, 1-1.3 mm, smooth, shiny.

  • Provided by: [F].Flora of North America @ efloras.org
    • Source: [
    • 4
    • ]. 

    "Monoecious; stem stout, erect, usually branched, to 2 m; plant scurfy-villous in and for some distance below the infl; lvs long-petioled, ovate or rhombic-ovate, usually hairy beneath at least along the veins, to 10( 15) cm in well developed plants; principal infl a terminal panicle of several or many short, densely crowded, obtuse spike-like thyrses, the whole 5–20 cm; similar but smaller panicles produced from the upper axils; bracts rigid, subulate, 4–8 mm, much surpassing the cal; sep 5, those of the pistillate fls oblong-lanceolate, slightly outcurved above, rounded or truncate or emarginate at the tip, and often minutely mucronate, with simple midvein, at maturity 3–4 mm and much-surpassing the fr; stamens 5; style-branches fairly long, erect or slightly recurved; fr compressed, 1.5–2 mm, circumscissile at the middle, the upper part rugulose; seed round-obovate, 1–1.2 mm; 2n=34. Native of tropical Amer., now a common weed throughout most of the U.S. and also in the Old World."

  • Provided by: [E].New York Botanical Garden
    • Source: [
    • 5
    • ]. 

    Morphology

    Perianth segments 5, those of the male flowers 1.75–2.25 mm., lanceolate-oblong, blunt to subacute, those of the female flowers 2–3 mm., narrowly oblong-spathulate to spathulate, obtuse or emarginate, more or less green-vittate along the midrib, which ceases below the apex or is excurrent in a short mucro.

  • Provided by: [C].Plants Of the World Online Portal - FZ
    • Source: [
    • 2
    • ]. 

    Stigmas 2–3, patent-flexuose or erect, c. 1 mm.

  • Provided by: [C].Plants Of the World Online Portal - FZ
    • Source: [
    • 2
    • ]. 

    Capsule subglobose, c. 2 mm., usually shorter than the perianth, circumcissile, with an indistinct neck, rugose below the lid.

  • Provided by: [C].Plants Of the World Online Portal - FZ
    • Source: [
    • 2
    • ]. 

    Leaves furnished with multicellular hairs along the lower surface of the primary venation and often the lower margins, long-petiolate (petioles up to c. 6 cm., in robust plants not rarely equalling the lamina), lamina ovate to rhomboid -or oblong-ovate, (1) 5–11 × (0.6) 3–6 cm., obtuse to subacute at the mucronulate apex, shortly cuneate to attenuate into the petiole.

  • Provided by: [C].Plants Of the World Online Portal - FZ
    • Source: [
    • 2
    • ]. 

    Seed black and shining, compressed, c. 1 mm., almost smooth centrally, faintly reticulate around the margins.

  • Provided by: [C].Plants Of the World Online Portal - FZ
    • Source: [
    • 2
    • ]. 

    Flowers in greenish or rarely somewhat pink-suffused, stout, axillary and terminal spikes, which are usually shortly branched to give a lobed appearance, more rarely with longer branches, the terminal inflorescence more or less paniculate, very variable in size, male and female flowers intermixed, the latter generally much more plentiful except sometimes at the apex of the spikes.

  • Provided by: [C].Plants Of the World Online Portal - FZ
    • Source: [
    • 2
    • ]. 

    Annual herb, erect or with ascending branches, (6) 15–80 (100)cm., simple or branched (especially from the base to about the middle of the stem).

  • Provided by: [C].Plants Of the World Online Portal - FZ
    • Source: [
    • 2
    • ]. 

    Stem stout, subterete to angled, densely furnished with multicellular hairs.

  • Provided by: [C].Plants Of the World Online Portal - FZ
    • Source: [
    • 2
    • ]. 

    Bracts and bracteoles lanceolate-subulate, pale-membranous with a prominent green midrib excurrent into a stiff, colourless arista, longer bracteoles subequalling to twice as long as the perianth.

  • Provided by: [C].Plants Of the World Online Portal - FZ
    • Source: [
    • 2
    • ]. 

    Distribution Map

     
    • Introduced distribution
    Introduced into
    • Southern America Brazil Bahia
    • Rio Grande do Norte
    • Paraní
    • Minas Gerais
    • São Paulo
    • Mato Grosso
    • Mato Grosso do Sul

    Other Local Names

    NameLanguageCountry
    Redroot pigweed, redroot amaranth, wild-beet amaranth, rough pigweed, common amaranth

     Information From

    Amaranthaceae
    World Flora Online Data. 2017.
    • A CC0 1.0 Universal (CC0 1.0).
    Brazilian Flora 2020 project - Projeto Flora do Brasil 2020
    http://floradobrasil.jbrj.gov.br
    Brazil Flora G (2014): Brazilian Flora 2020 project - Projeto Flora do Brasil 2020. v393.147. Instituto de Pesquisas Jardim Botanico do Rio de Janeiro. Dataset/Checklist. doi:10.15468/1mtkaw
    • B Group Brazil Flora, REFLORA Program
    Plants Of the World Online Portal - FZ
    https://www.kew.org/science/who-we-are-and-what-we-do/strategic-outputs-2020/plants-of-the-world-online
    http://www.plantsoftheworldonline.org/terms-and-conditions
    • C
    Flora Of CHina @ efloras.org
    http://www.efloras.org/flora_page.aspx?flora_id=2
    'Flora of China @ eFloras (2008). Published on the Internet http://www.efloras.org/flora_page.aspx?flora_id=2 [accessed August 2016]' Missouri Botanical Garden, St. Louis, MO & Harvard University Herbaria, Cambridge, MA.
    • D Missouri Botanical Garden
    New York Botanical Garden
    Descriptions of plants should be attributed to the full citation for each individual article, chapter or book that is the source for each record, which should include the authors of original publication.
    • E Content licensed under Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License
    Flora of North America @ efloras.org
    http://www.efloras.org/flora_page.aspx?flora_id=1
    'Flora of North America @ eFloras (2008). Published on the Internet http://www.efloras.org/flora_page.aspx?flora_id=1 [accessed August 2016]' Missouri Botanical Garden, St. Louis, MO & Harvard University Herbaria, Cambridge, MA.
    • F Flora of North America Association
    World Flora Online consortium
    http://www.worldfloraonline.org/organisation/WFO
    World Flora Online Data. 2018.
    • G CC0 1.0 Universal (CC0 1.0).