Plants annual, pubescent in distal parts or becoming glabrescent at maturity. Stems erect to ascending or decumbent, branched at or distal to base, 0.1-0.9 m. Leaves: petiole variable in length; blade lanceolate to nearly linear or rhombic-ovate to elliptic-ovate, (1.5-)2-4(-5) × 1-3 cm, base cuneate to broadly cuneate, margins entire, plane, rarely indistinctly undulate, apex subacute to obtuse or emarginate, mucronulate. Inflorescences axillary glomerules, green. Bracts lanceolate, subspinescent, 1.5-2 mm, shorter or slightly longer than tepals. Pistillate flowers: tepals 3, erect, elliptic to lanceolate-elliptic, equal or subequal, 1.5-2 mm, apex short-acuminate; style branches slightly spreading; stigmas (2-)3. Staminate flowers intermixed with pistillate; tepals 3, equal or subequal; stamens 3. Utricles subglobose to broadly elliptic, 2-2.5 mm, slightly rugose, dehiscence regularly circumscissile, rarely irregularly dehiscent. Seeds black, lenticular, 1-1.3(-1.6) mm diam., smooth or indistinctly punctate. Flowering summer-fall. On ballast; 0 m; introduced; N.J.; native to Eurasia (Mediterranean area, s Asia); n Africa; locally introduced in Australia. In North America the name Amaranthus graecizans has been constantly misapplied to the common North American taxa A. albus and A. blitoides. Consequently, A. graecizans has been excluded from lists of North American plants. Recently, herbarium specimens (casual aliens collected in 1879 on ballast in Camden, New Jersey) of A. graecizans subsp. sylvestris were discovered (M. Costea et al. 2001b). Probably, the species disappeared in North America long ago, but, considering the long history of misidentification and confusion, there is also some chance that it may occur locally as an introduced species. Three subspecies are usually recognized within Amaranthus graecizans in the Old World: subsp. graecizans, subsp. sylvestris (Villars) Brenan, and subsp. thellungianus (Nevski) Gusev. Only subsp. sylvestris, characterized by rhombic-ovate to elliptic-ovate leaves (as compared to lanceolate to almost linear leaves in subsp. graecizans) and comparatively large seeds has so far been reported from North America.
Despite its superficial similarity to Amaranthus albus and A. blitoides, A. graecizans seems to be more closely related to other Old World taxa with trimerous flowers.