The genus Oryza contains 26 recognized species, of which 24 are wild species and two (O.sativa and O.glaberrina) are cultivated (Vaughan, 2003). The wild progenitors of O.sativa and the Asian common wild rice, show wide variation in their habit ranging from annuals to perennial. The Asian common wild rice are O.rufipogan and O. nivara. Annual forms might have gradually developed in plateau regions of eastern India, South-east Asia and Southern China. During the course of time, they differentiated into two egocentric groups, namely O.indica and O.japonica .The O. japonica subspecies further differentiated into tropical and temperate japonica. The schematic representation of evolutionary pathway of the Asian cultivated rice is shown below.
|Taxonomy of rice|