Abstract: In the study of plant systematics and evolution, the gene sequences of mitochondrial genome are less used for their low informative sites and complex structure compared to those of the nuclear and chloroplast genomes. In this study, we sequenced the intron 2 of mitochondrial nad1 gene to study the phylogeny of Oryzeae, in particular emphasizing the systematic position of Porteresia, a monotypic genus of Oryzeae with the only species P. coarctata. The results indicate that the tribe Oryzeae should be divided into two subtribes (Oryzinae and Zizaniinae) and that Leersia is the most closely related genus to Oryza. The present data clearly demonstrate that Porteresia coarctata should be treated as a member in Oryza rather than as a separate genus. The sequences of nad1 intron 2 are informative enough in Oryzeae, and thus appear appropriate for the phylogenetic study at higher taxonomic levels. The gaps, when treated appropriately, can provide additional information in phylogenetic study.

Key words: nad1 intron, gap, mitochondrial DNA, Porteresia coarctata, Oryzeae, phylogeny.