The genus Oryza contains 25 recognized species, of which 23 are wild species and two (O.sativa and O.glaberrina) are cultivated (Morishma 1984; Vaughan, 1994; Bar and Khush, 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 rices are O.rufipogan and O. nivara (Chang 1985). 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 (Chang 1986). 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.

Reference

1. Vaughan, Duncan A., H. Morishima, and K. Kadowaki. "Diversity in the Oryza genus." Current opinion in plant biology6.2 (2003): 139-146.