On the phylogeny and biogeography of the genus Oryza

The genus Oryza that gave rise to rice has a distinctive phylogenetic position within the Poaceae (Graminae). Recently there has been much progress in understanding the phylogenetic relationships of angiosperms. In this review current understanding of angiosperm and monocot phylogeny is discussed in relation to the emergence of Oryza. The lineage leading to Oryza arose early in the evolution of grasses that evolved after 70 mya. Since grasses arose well after the split of Gondwanaland, Oryza did not originate on Gondwanaland and continental drift did not play a role in Oryza biogeography. A new hypothesis is presented to explain the present day distribution of Oryza species. The role of animals, including birds, in the distribution of Oryza spread from a core centre of Oryza diversity in Southeast Asia and New Guinea is the basis for this hypothesis. Humans are also thought to have played a role in distribution of Oryza species particularly in historic times. Finally the continuing evolution of the genus Oryza is discussed. The wild relatives of rice can provide continuously evolving gene resources for rice improvement only if there is a substantial effort to conserve them in situ.