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 im-
portance in the agricultural production, the genus Oryza has attracted much attention of many taxon-
omists, 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 tax-
onomic 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 ge-
nus 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, geo-
graphic distribution, and genome constitution of each species. This system not only adopted a rea-
sonable 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 taxon-
omy with a morphological key to species. We also discussed the existing problems in the taxonomy of
the genus Oryza.
