Inflorescence spicate or racemose or flowers in clusters, rarely reduced to a single flower. Flowers generally actinomorphic, bisexual or less often unisexual. Perianth segments 3–5, free or variously fused. Stamens 5, sometimes reduced in number with staminodes present, sometimes staminodes alternate with stamens; filaments frequently fused, at least partially. Ovary superior, 1-locular, ovules 1 or several; style 1, entire, bifid or trifid.
| | Key to the genera | |
| 1 | Leaves alternate or all radical | 2 |
| Leaves opposite | 4 |
| 2 | Woody climbers; fruit a red berry | Deeringia |
| Annual or perennial herbs or subshrubs; fruit dry
Back to 1 | 3 |
| 3 | Inflorescence and perianths mostly glabrous; filaments free; fruit 1-seeded | Amaranthus |
| Inflorescence and perianths variously hairy; filaments fused at the base; fruit with 1 or more seeds
Back to 2 | 10 |
| 4 | Perianth rigid, especially in fruit | 5 |
| Perianth membranous or scarious in fruit, not rigid
Back to 1 | 8 |
| 5 | Perianth segments 4; bracts spinescent, spreading in fruit | Nyssanthes |
| Perianth segments 5; bracts variously armed, not spreading in fruit
Back to 4 | 6 |
| 6 | Inflorescence an axillary cluster | Alternanthera |
| Inflorescence a terminal spike
Back to 5 | 7 |
| 7 | Flowers not reflexed in fruit; bracts not pungent | Froelichia |
| Flowers reflexed in fruit; bracts pungent
Back to 6 | Achyranthes |
| 8 | Stigma bifid; at least some bracts subequal to perianth | Gomphrena |
| Stigma entire; bracts shorter than perianth
Back to 4 | 9 |
| 9 | Perianth segments fused to c. halfway; inflorescence woolly | Guilleminea |
| Perianth segments free or almost so; perianths glabrous or variously hairy but inflorescence not woolly
Back to 8 | Alternanthera |
| 10 | Fruit with 2 or more seeds; flowers mostly in simple terminal spicate inflorescences; anthers 2-locular | Ptilotus |
| Fruit with 1 seed; flowers in terminal and lateral spicate inflorescences; anthers 4-locular
Back to 3 | Aerva |
