Abstract: The genus Oryza L. is one of the most important plant groups in the grass family (Poaceae), which includes more than 20 species and is distributed in tropics and subtropics of the world. The future breakthrough of rice breeding relies greatly on the exploration and utilization of rich germplasm in the rice genepool, particularly the wild rice species. Because of its significant importance in the agricultural production, the genus Oryza has attracted much attention of many taxonomists, geneticists, breeders, and molecular biologists for various kinds of research. During the last two hundred and fifty years since the first description of the genus Oryza by Linnaeus, great changes have taken place in the genus in terms of number of species and taxonomic status. Many taxonomists have made extensive researches on species circumscription and taxonomic ranking at the subgenus level, which was essential for the establishment of the modern taxonomic systems of Oryza. The taxonomic system established by Roschevicz (1931) based on his comprehensive and detailed studies on plant specimens and literature provided an important foundation for the modern taxonomy of the genus Oryza. Sharma & Shastry (1965) offered a taxonomic system of Oryza, which was essentially influenced by that of Roschevicz. This system treated subgenus rank properly, but their definition of Oryza was in a much wider sense and several species in this system have been excluded from the current Oryza. Vaughan (1989) extensively studied and compared Oryza samples from all over the world and provided a taxonomic system including updated data such as morphological variation, geographic distribution, and genome constitution of each species. This system not only adopted a reasonable generic definition, but also provided a good reference of species relationship. Unfortunately, the subgenus rank “complex” used by Vaughan (1989) does not have any legitimate standing in the International Code of Botanic Nomenclature (ICBN). Lu (1999) summarized the major taxonomic studies of previous authors including new species published in Oryza over the past ten years, and proposed an Oryza taxonomic system with 3 sections, 7 series and 24 species. We provided in this paper the most updated studies of the Oryza species and suggested a revised version of Oryza taxonomy with a morphological key to species. We also discussed the existing problems in the taxonomy ofthe genus Oryza.

Key words: Poaceae, Oryzeae, Oryza, Taxonomy, Species relationship, Morphology