Piaropus Rafinesque, nom. rej.
Herbs annual or perennial, aquatic, floating or creeping, rooting from nodes. Leaves rosulate or alternate; petiole long, rarely inflated; leaf blade cordate, broadly ovate-rhomboidal, or linear-lanceolate. Inflorescences terminal, erect during anthesis but then reflexed, pedunculate, spiciform or paniculate, 2- to many flowered. Flowers zygomorphic or subactinomorphic. Stamens 6, inserted on proximal part of perianth, often 3 longer and 3 shorter; filaments filiform, hairy; anthers dorsifixed, oblong. Ovary sessile, 3-loculed; ovules numerous per locule. Style filiform, curved; stigma slightly dilated or very shortly 3- or 6-lobed. Capsule ovoid, oblong, or linear-fusiform, included in marcescent perianth tube; pericarp membranous. Seeds numerous, longitudinally winged, cross striate.
Seven species: mainly in tropical America, one species in tropical Africa; one species (introduced) in China.