Small, perennial, aquatic herb, 30-50 cm, stems and branches terete, hollow, rooting at nodes; leaves sessile, opposite, 3-8 cm long, linear-lanceolate, acute at apex, narrowed at base; flowers in axillary, apical heads small, on long peduncles up to 2-5 cm long ; bracts scarious, white, deltoid-ovate, bracteoles as long as bracts, persistent; tepals 5, white, elliptic equal, 6-7 mm long, acuminate; stamens 5, all fertile, anthers 1-celled, filaments connate below; ovary 1-celled, ovule solitary, pendulous, style slender, stigma capitate; utricles obcordate with thickened margins; seeds discoid, brown.