Description: Annual or perennial herbs of aquatic marshy habitats; stems branched.
Leaves whorled or opposite, sessile or subsessile.
Flowers actinomorphic, 3–5-merous; solitary in axils of bracts, somtimes in axillary or terminal spikes or racemes. Hypanthium campanulate. Calyx 3–6-lobed, with or without alternating appendages. Petals 3–6 or absent, inconspicuous, white or pink. Stamens 1–6. Ovary 2–4-locular.
Fruit a septicidal capsule, opening by 2–4 valves; seeds many, minute.
Distribution and occurrence: World: 45 spp., trop. to temp. regions, especially Asia. Aust.: 6 spp. (2 spp. endemic, 3 spp., native, 1 sp. naturalized), Qld, N.S.W., N.T., W.A.
Text by J. Highet & Peter G. Wilson
Taxon concept:
| | Key to the species | |
| 1 | Leaves ovate to lanceolate; flowers in axils of leaf-like bracts, scattered along stems; petals ± elliptic, ± colourless; capsule opeing by 3 valves. | Rotala tripartita |
| Leaves broad-elliptic to circular; flowers in terminal, many-flowered spikes; petals obovate, mauve to pink; capsule opening by 4 valves. | Rotala rotundifolia |
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