Oryza nivara is a possible wild progenitor of the cultivated rice Oryza sativa. It was separated from Oryza rufipogon in 1965; however, the separation has been questioned, and some sources treat it as a synonym of O. rufipogon. It may be treated as the annual form of O. rufipogon. For those who accept it as a separate species, it is an annual, short to intermediate height (usually <2 m) grass; panicles usually compact, rarely open; spikelets large, 6–10.4 mm long and 1.9-3.4 mm wide, with strong awn (4–10 cm long); anthers 1.5–3 mm long. It grows in shallow water up to 0.3 m, in seasonally dry and open habitats. It is found growing in swampy areas, at edge of pond and tanks, beside streams, in ditches, in or around rice fields.

Distribution

Its distribution includes Bangladesh, Cambodia, China, India, Laos, Malaysia, Myanmar, Nepal, Sri Lanka, Thailand, and Vietnam.

Genome

The genome of O. nivara was first sequenced in 2015. Stein et al., 2018 sequenced the genomes of O. nivara and other domesticated and wild relatives. They produced reference assemblies and analyses for divergence time and genetic distance. (The O. nivara assembly is 338 Mb.) They demonstrated that this species and Oryza sativa subsp. indica are most closely related and that the same is true for Oryza sativa subsp. japonica and Oryza rufipogon.<ref name="Analyze genomes of crops and crop wild relatives">