Herbs, shrubs (rarely small trees), annual or perennial, monoecious, dioecious, or polygamous, evergreen or deciduous. Roots fibrous, taprooted, sometimes fusiform or bulbous, fleshy and thickened in Beta. Stems sometimes succulent and apparently jointed, or with slippery and aromatic bark, sometimes spiny, alternate or opposite; pubescence silvery, sometimes stellate or glandular, often scurfy from inflated salt glands that senesce into white flakes. Leaves simple, usually alternate, occasionally opposite, lacking stipules, petiolate or sessile, sometimes reduced to small scales, or fleshy; blade linear to broadly triangulate in outline, margins entire to serrate, serrate-dentate, or lobed. Inflorescences: flowers solitary or clustered in axillary or terminal glomerules or in short, cylindric spikes; bracts absent or 1-5, deciduous or persistent, of various shapes. Flowers bisexual or unisexual, uniseriate, radially or rarely bilaterally symmetric; bracteoles absent or 1-5, connate basally, green; perianth segments 5, sometimes 1 or absent, green, inconspicuous, fleshy in Salicornia and Sarcocornia, strongly imbricate in Nitrophila; petals absent; stamens absent or 1-5, usually as many as and opposite perianth lobes; pistils absent or (1-)2(-3); styles 1-3, sometimes with stylopodium; ovary usually superior, half-inferior in Sarcobatus, inferior and connate with receptacle in fruit in Beta, 1-locular with single, basally attached ovule. Fruiting structures: bracteoles or fruiting bracts brown, black, or reddish brown, monomorphic or sometimes dimorphic; perianth segments deciduous or persistent in mature fruits and of various shapes and ornamentation, accrescent around fruits; fruits achenes or utricles, vertical or horizontal within perianth parts, pericarp (ovary wall) adherent or nonadherent, chartaceous or papery, sometimes reticulate, mottled or smooth. Ovules usually 1, campylotropous, bitegmic, crassinucellate. Seeds 1 per flower, black, brown, reddish brown, or mixture, flattened vertically or rounded, margins winged or not winged, surfaces smooth and shiny or reticulate, regulate, verrucate, prickly, or indistinct, morphology variable and strongly influenced by plant photoperiod; seed coat smooth, striate, or verrucate when pericarp is removed; embryo large, curved to annular or spirally coiled; radicle position median or basal, ascending or p A number of species introduced from Europe and Asia are weedy in North America. The widespread distribution of the family in the deserts of Eurasia and Australia is indicative of the ancient status of the family. Fossil pollen from this family dates to the Maestrichtian, providing the oldest known fossils in the Caryophylliidae. Plants in this family typically have Crassulacean Acid Metabolism, have either a C₃ or C₄ photosynthetic pathway (W. V. Brown 1975; G. W. Welkie and M. Caldwell 1970), accumulate organic acids, free nitrates, and oxalates, and often contain alkaloids. Along with other members of the Caryophyllales, members of the family contain pigments called betalains (named for the genus Beta) rather than anthocyanins.

Economically important members of this family include spinach and chard (Spinacia oleracea) and beets (Beta vulgaris). Seeds in this family generally provide a rich source of protein, and one species, Chenopodium quinoa, is gaining widespread acceptance as a cereal crop. Toxicity from high levels of nitrates or oxalates has been reported for a number of species (J. M. Kingsbury 1964), and the pollen is known to be allergenic (T. C. Fuller and E. McClintock 1986). The nutritional characteristics of many species that we share with northern Asia were described by M. M. Iljin (1936).

Molecular and morphologic studies provide evidence supporting the inclusion of the Chenopodiaceae within Amaranthaceae (Angiosperm Phylogeny Group 1998; W. S. Judd and I. K. Ferguson 1999; J. E. Rodman 1990). However, until discordant elements within these lineages, such as Sarcobatus (H.-D. Behnke 1997), are interpreted within a larger evolutionary scheme, the disposition of family groups remains problematic.

Herbs, rarely subshrubs, annual or perennial; trichomes simple (branched in Tidestromia). Stems without nodal spines (Amaranthus spinosus sometimes with paired nodal spines). Leaves alternate or opposite, exstipulate, usually petiolate; blade margins entire (entire or serrulate in Iresine; entire, crispate, or erose in Amaranthus). Inflorescences cymules arranged in spikes, panicles, thyrses, heads, glomerules, clusters, or racemes; each flower subtended by 1 bract and 2 bracteoles (latter sometimes 1 or absent in Amaranthus). Flowers bisexual or unisexual (plants then monoecious or dioecious), hypogynous, generally small or minute; tepals mostly (1-)4-5 or absent, distinct or connate into cups or tubes, scarious, chartaceous, membranaceous, or indurate; stamens 2-5, filaments basally connate into cups or tubes, rarely distinct, alternating with pseudostaminodes (appendages on staminal tubes) or not, anthers 2-locular with 1 line of dehiscence or 4-locular with 2 lines of dehiscence; ovary superior, 1-locular; ovules 1 or, rarely, 2-many; style 1 or absent; stigmas 1-3(-5). Fruits utricles, dry, dehiscent or not. Seeds black, reddish brown, or brown, lenticular, subglobose or globose (rarely cylindric), usually small; embryo peripheral, surrounding mealy perisperm. Centers of diversity for Amaranthaceae are southwestern North America, Central America, South America, and Africa south of the Sahara Desert. Generic limits are not well defined in some groups; fewer than 60 or more than 70 genera could be recognized. Some species occur in severe habitats such as sandy, calcareous, gypseous, saline, or serpentine soils in deserts, semideserts, and seashores. Some species are weedy, including the major agricultural weeds in Amaranthus. Some species are cultivated as ornamentals, particularly Amaranthus caudatus (love-lies-bleeding), A. hypochondriacus (prince´s-feather), A. tricolor (Joseph´s-coat), Celosia cristata (cockscomb), and Gomphrena globosa (globe-amaranth). Native Americans domesticated white-seeded grain amaranths (A. caudatus, A. cruentus, and A. hypochondriacus) for use as cereal grains. Some species of Amaranthus and Celosia are potherbs.

Amaranthaceae are usually divided into subfamilies Amaranthoideae (anthers 4-locular with two lines of dehiscence) and Gomphrenoideae Schinz (anthers 2-locular with one line of dehiscence). Amaranthaceae and Chenopodiaceae have long been recognized as allied families that share a number of features: generally small flowers, one perianth whorl, a syncarpous gynoecium with a superior ovary and often only one ovule, basal or free-central placentation, pollen characteristics, centrospermous embryo development, betalain pigments, and P-type form (c) sieve-element plastids.

Herbs, vines or shrubs, rarely trees. Stems sometimes jointed or succulent. Leaves opposite and spiral, or alternate, simple, exstipulate, with pinnate venation, generally entire or undulate (sometimes serrate or lobed), sometimes succulent. Inflorescences determinate, terminal, axillary. Flowers are generally bisexual (less commonly unisexual), usually actinomorphic, tepals 3-5, usually distinct, rarely basally connate, stamens 3-5, antesepalous, filaments distinct or basally connate and forming a tube. Ovary usually superior (rarely half inferior) with basal placentation, carpels usually 2 or 3, connate, 1 locule. Nectar disk often present. Fruit is a nutlet, berry, irregularly dehiscing capsule, circumscissile capsule, or multiple fruit. This family absorbed Chenopodiaceae in its entirety.