Description:

• Annual or rarely perennial herbs, erect or decumbent, glabrous or furnished with short and gland-like or multicellular hairs; plants monoecious or dioecious
• Leaves alternate, simple, entire or sinuate, long-petiolate
• Inflorescences basically cymose, of dense to lax axillary thyrses or upper clusters dense, leafless, aggregated and spike-like, bracteate
• Flowers unisexual or bisexual; bracteoles 2-5, small and herbaceous or membranous and spinescent
• Tepals (1-3)5, glabrous, membranous, equal or subequal, free or connate below and somewhat indurate, occasionally absent in flowers of dioecious spp
• Stamens as many as tepals; filaments free at base; pseudostaminodes absent; anthers 2-thecous
• Ovary ellipsoid, compressed; ovule solitary, subsessile, erect; style short or absent; stigmas 2 or 3, subulate or filiform
• Fruit a dry capsule, usually enclosed in perianth, indehiscent or circumscissile, sometimes 2- or 3-toothed at apex
• Seed globose or compressed, black, smooth and shiny; testa thin; embryo annular; endosperm present
• x = 17, 8 (7, 9, 10, 12) (high polyploidy)

Classification Notes:

• A difficult genus, complicated by the cultivation of some species (e.g. A. lividus L. and A. tricolor L.) as green vegetables and others (especially A. caudatus L. and A. hybridus L. agg.) as grain crops
• It is also a genus prone to hybridisation, though probably the frequency of natural hybrids has been overestimated

Nomenclature:

• Amaranthus L.
  • Linnaeus: 989 (1753)
  • Linnaeus: 427 (1754)
  • Brown: 414 (1810)
  • Hooker: 28 (1880)
  • Schinz: 102 (1893)
  • Baker & Clarke: 30 (1909)
  • Cooke & Wright: 408 (1910)
  • Adamson: 191 (1936)
  • Adamson: 360 (1950)
  • Aellen: 465 (1959)
  • Aellen: 109 (1964)
  • Podlech: 8 (1966)
  • Townsend: 471 (1974)
  • Townsend: 63 (1977)
  • Brenan: 451 (1981)
  • Townsend: 20 (1985)
  • Townsend: 45 (1988)
  • Townsend: 143 (1993a)
  • Townsend: 81 (1993b)

Distribution & Notes:

• Global: Species ± 60, tropical and warm temperate regions of both Old and New World, sporadic as weeds in cooler temperate areas
• Southern Africa: Species 15 native and introduced, mostly widespread weeds of cultivation