Flora of North America species comparison

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Amaranthus tuberculatus

common waterhemp, rough-fruit amaranth, rough-fruit water-hemp, tall water-hemp
Stems

erect to sometimes ascending or rarely prostrate, branched, rarely simple, usually (0.5–)1–2(–3) m. Leaves: petiole 1/4–1/2 length of blade;

blade ovate or obovate proximally, oblong or elliptic to narrowly lanceolate distally, 1.5–15 × 0.5–3 cm, base cuneate, margins entire, plane, apex obtuse or rounded to acute.
Bracts

of pistillate flowers 1–2 mm; of staminate flowers with inconspicuous to prominent midrib, 1–2 mm, apex acuminate to short-subulate.
Inflorescences

terminal, linear spikes to panicles, occasionally interrupted-moniliform, remote, globose glomerules.
Staminate flowers

tepals 5, inner tepals with prominent midribs excurrent as rigid spines or not, equal to unequal, 2–3 mm, apex obtuse to acute or acuminate or indistinctly mucronulate;

stamens 5.
Pistillate flowers

tepals absent or 1–2, often rudimentary, 1–3 mm;

style branches ± erect;

stigmas 3.
Seeds

dark reddish brown to dark brown, 0.7–1 mm diam., shiny.
Utricles

dark brown to reddish brown, not ribbed, obovoid to subglobose, 1.5–2 mm, thin, almost smooth or irregularly rugose, indehiscent, irregularly dehiscent, or dehiscence regularly circumscissile.

Amaranthus tuberculatus
Phenology Flowering summer–fall.
Habitat Wet areas, such as margins of rivers, ponds, marshes, lakes, and creeks, disturbed habitats, such as agricultural fields, roadsides, and railroads
Elevation 0-1000 m (0-3300 ft)
Distribution
from FNA
AL; AR; CA; CO; CT; DE; GA; IA; ID; IL; IN; KS; KY; LA; MA; MD; ME; MI; MN; MO; MS; NC; ND; NE; NH; NM; NV; NY; OH; PA; SC; SD; TN; TX; VT; WA; WI; WV; MB; ON; PE; QC [Introduced in North America; introduced, usually not naturalized, in Europe and other continents]
[WildflowerSearch map]
[BONAP county map]
Discussion

J. D. Sauer (1967b, 1972b) separated Amaranthus rudis (A. tamariscinus) as distinct from A. tuberculatus, based primarily on absence of tepals in the pistillate flowers and indehiscent fruits. Recent work by D. B. Pratt and L. G. Clark (2001) showed that those characteristics are not constant and they recognized only one polymorphic species, A. tuberculatus. Long-term observations by K. R. Robertson strongly support the inclusion of A. rudis within A. tuberculatus. Amaranthus rudis probably was originally native to the Great Plains west of the Mississippi, from Texas to Iowa. Amaranthus tuberculatus likely had a more northern range, north of Missouri and Tennessee to the Great Lakes. The emerging evolutionary differentiation between the two related taxa was erased by agriculture and human-induced introduction and invasion. Amaranthus tuberculatus has become a major weed of agricultural fields and other disturbed habitats and is now introduced in parts of North America far outside its original range.

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Source FNA vol. 4.
Parent taxa Amaranthaceae > Amaranthus > subg. Acnida > sect. Acnida
Sibling taxa
A. acanthochiton, A. albus, A. arenicola, A. australis, A. blitoides, A. blitum, A. californicus, A. cannabinus, A. caudatus, A. crassipes, A. crispus, A. cruentus, A. deflexus, A. dubius, A. fimbriatus, A. floridanus, A. graecizans, A. greggii, A. hybridus, A. hypochondriacus, A. muricatus, A. obcordatus, A. palmeri, A. polygonoides, A. powellii, A. pumilus, A. retroflexus, A. scleropoides, A. spinosus, A. tamaulipensis, A. thunbergii, A. torreyi, A. tricolor, A. viridis, A. viscidulus, A. watsonii, A. wrightii
Synonyms Acnida tuberculata, Acnida altissima, Acnida altissima var. prostrata, Acnida altissima var. subnuda, Acnida concatenata, Acnida subnuda, Acnida tamariscina, Acnida tamariscina var. concatenata, Acnida tamariscina var. tuberculata, A. ambigens, A. rudis
Name authority (Moquin-Tandon) J. D. Sauer: Madroño 13: 18. (1955)
Web links 
Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



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