Madroño 13: 18. 1955
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
Man., Ont., P.E.I., Que., Ala., Ark., Calif., Colo., Conn., Del., Ga., Idaho, Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Nebr., Nev., N.H., N.Mex., N.Y., N.C., N.Dak., Ohio, Pa., S.C., S.Dak., Tenn., Tex., Vt., Wash., W.Va., Wis., introduced, usually not naturalized, in Europe and other continents.
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.