Most species in the Amaranthaceae are annual or perennial herbs or subshrubs; others are shrubs; very few species are vines or trees. Some species are succulent. Many species have stems with thickened nodes. The wood of the perennial stem has a typical "anomalous" secondary growth; only in subfamily Polycnemoideae is secondary growth normal.
The leaves are simple and mostly alternate, sometimes opposite. They never possess stipules. They are flat or terete, and their shape is extremely variable, with entire or toothed margins. In some species, the leaves are reduced to minute scales. In most cases, neither basal nor terminal aggregations of leaves occur.
The flowers are solitary or aggregated in cymes, spikes, or panicles and typically perfect (bisexual) and actinomorphic. Some species have unisexual flowers. Bracts and bracteoles are either herbaceous or scarious. Flowers are regular with an herbaceous or scarious perianth of (one to) mostly five (rarely to eight) tepals, often joined. One to five stamens are opposite to tepals or alternating, inserting from a hypogynous disc, which may have appendages (pseudostaminodes) in some species. The anthers have two or four pollen sacs (locules). In tribe Caroxyloneae, anthers have vesicular appendages. The pollen grains are spherical with many pores (pantoporate), with pore numbers from a few to 250 (in Froelichia) One to three (rarely six) carpels are fused to a superior ovary with one (rarely two) basal ovule.
The diaspores are seeds or fruits (utricles), more often the perianth persists and is modified in fruit for means of dispersal. Sometimes even bracts and bracteoles may belong to the diaspore. More rarely the fruit is a circumscissile capsule or a berry. The horizontal or vertical seed often has a thickened or woody seed coat. The green or white embryo is either spirally (and without perisperm) or annular (rarely straight).