Description: Annual or perennial herbs, with prostrate or ascending stems.
Leaves opposite.
Inflorescence globose to ovoid, axillary or terminal, usually of 1–several spikes, these sometimes clustered. Flowers bisexual, each subtended by a small bract and 2 bracteoles. Perianth segments 5, scarious and white. Stamens 5 (or a few reduced to staminodes), fused at the base. Ovary sessile, flattened to globose; style short or not developed; stigma capitate.
Fruit indehiscent, compressed, with an apical notch, 1-seeded.
Distribution and occurrence: World: c. 200 species, tropical & subtropical regions. Australia: 8 or 9 species, all States.
Text by S. W. L. Jacobs & L. Lapinpuro
Taxon concept:
| | Key to the species | |
| 1 | Inflorescence pedunculate, axillary or terminal; peduncles to 4 cm long | Alternanthera philoxeroides |
| Inflorescence sessile, axillary | 2 |
| 2 | Perianth segments unequal; outer 2 c. 4–5 mm long, acuminate, pungent; next inner narrower, c. 3 mm, apex toothed with midrib excurrent; 2 innermost to c. 2.5 mm long, acute, sigmoid, with dorsal tuft of hairs at first bend | Alternanthera pungens |
| Perianth segments more or less equal
Back to 1 | 3 |
| 3 | Perianth segments woolly on the midback | Alternanthera angustifolia |
| Perianth segments mostly glabrous, or sometimes with a few hairs along back of midrib
Back to 2 | 4 |
| 4 | Perianth segments 4–5 mm long, lanceolate, with long, tapered, acute apex | Alternanthera nodiflora |
| Perianth segments 2–3 mm long, lanceolate or oblong, acute
Back to 3 | 5 |
| 5 | Innermost bracts lanceolate, acuminate, 1.5–2.5 mm long; perianth segments lanceolate | Alternanthera denticulata |
| Innermost bracts ovate, acute, to 1.5 mm long; perianth segments oblong
Back to 4 | 6 |
| 6 | Leaves lanceolate to oblanceolate or elliptic, 15–25 mm long, 6–10 mm wide | Alternanthera nana |
| Leaves ovate to oblong-ovate or obovate, 5–50 mm long, 3–6 mm wide
Back to 5 | Alternanthera sp. A Flora of New South Wales (M.Gray 5187) |
|
