Plants perennial; aquatic, producing long, floating culms; synoecious. Culms 50-150 cm, spongy, developing adventitious roots at the nodes, branched; branches erect, leafy. Leaves cauline, glabrous, veins tessellate; sheaths open, inflated, serving as floats; ligules absent or hyaline; pseudopetioles present; blades elliptic, ovate, ovate-lanceolate, or oblong. Inflorescences terminal panicles, aerial, lowermost branches whorled; disarticulation beneath the spikelet calluses. Spikelets bisexual, laterally compressed, with 1 floret. Glumes absent or an annular rim; calluses (1)2-10 mm, stipelike, glabrous, junction with the pedicels marked by a tan constriction; lemmas 5-veined, margins clasping the paleas, apices acuminate, awned, awns terminal, antrorsely scabridulous; paleas similar to the lemmas, 3-veined, 1-keeled, acute-acuminate, unawned; lodicules 2, glabrous; anthers 6; styles 2, bases not fused, stigmas laterally exserted, plumose. Caryopses terete, fusiform; embryos small; hila linear, almost as long as the embryo, x = 12.
Discussion
Hygroryza is a monospecific Asian genus that grows in India, Ceylon, and throughout southeast Asia. It forms floating masses, often of considerable extent, in lakes and slow-moving streams, and is sometimes a weed in rice.