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Published In: Species Plantarum 2: 991. 1753. (1 May 1753) (Sp. Pl.) Name publication detailView in BotanicusView in Biodiversity Heritage Library

Project Name Data (Last Modified On 8/4/2017)
Acceptance : Accepted
Project Data     (Last Modified On 7/9/2009)
Status: Native


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11. Amaranthus retroflexus L. (rough green amaranth, rough pigweed)

Pl. 197 g; Map 820

Plants monoecious. Stems 30–200 cm long, erect or ascending, sparsely to densely pubescent toward the tip with mostly crinkled, multicellular hairs, unarmed. Leaves mostly long-petiolate. Leaf blades 2–12 cm long, lanceolate to ovate or elliptic, narrowed or tapered to a usually bluntly pointed tip (often minutely notched at the very tip), narrowed or tapered at the base, the surfaces sparsely to moderately pubescent mostly along the veins with inconspicuous, mostly crinkled, multicellular hairs, the upper surface sometimes glabrous or nearly so. Inflorescences dull or grayish green occasionally dull reddish-tinged; axillary and terminal; the axillary inflorescences short spikes or less commonly dense, globose clusters; the terminal inflorescence usually a panicle with numerous clusters of short, dense spikes (these branching along most of the panicle axis); the flowers mostly continuous along the spikes; the tip straight and usually stiffly erect; the main axis and branches moderately to densely pubescent with mostly crinkled, multicellular hairs. Bracts 4–8 mm long, the main body (excluding the awn) conspicuously longer than the sepals and fruits, lanceolate to ovate, narrowed or tapered to a sharply pointed tip, with a strongly thickened green midrib and relatively narrow, thin, papery margins, the midrib extending beyond the main body as a short awn, spinelike at maturity. Staminate flowers with (4)5 more or less similar sepals, these 2.0–2.6 mm long, slightly outward-curved, lanceolate to oblong-ovate, narrowed or tapered to a sharply pointed tip, usually tapered to a short, awnlike extension of the midrib at the tip. Stamens (4)5. Pistillate flowers with (4)5 more or less similar sepals, these 2.2–3.0 mm long, outward-curved, narrowly oblong to narrowly oblong-elliptic, truncate, rounded or shallowly notched at the soft tip, sometimes with an abrupt, minute, sharp extension of the midrib. Stigmas 3, erect or ascending. Fruits 1.8–2.2 mm long, with circumscissile dehiscence, the surface finely wrinkled above the midpoint when dry. Seeds 0.9–1.2 mm in diameter, rounded along the rim, the surface reddish brown to more commonly black. 2n=34. June–October.

Scattered, mostly south of the Missouri River (native of most of North America and portions of South America; introduced in Europe, Asia, Africa). Tops of bluffs and upland prairies; crop fields, fallow fields, gardens, levees, pastures, farmyards, feedlots, roadsides, railroads, and open, disturbed areas.



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