Abstract: Nuclear rRNA genes (rDNA) in angiosperms are arranged in long tandem repeat ing units, much like those of other higher eukaryotes. Owing to rapid concerted evolution, the repeat units have homogenized or nearly so in most species. The internal transcribed spacer (ITS) of nuclear rDNA is composed of ITS1 and ITS2, which are seperated by 5.8S rDNA. The two spacers, ITS1 (187～298 bp) and ITS2 (187～252 bp), can be readily amplified by PCR and sequenced using universal primers. The sequences contain many vari able sites and potential informative sites among related species, and have been proven to be a useful molecular marker in phylogenetic and evolutionary studies of many angiosperm taxa. It can be used not only in classification and phylogenetic inferences at the levels of family, subfamily, tribe, genus and section, but also in reconstruction of reticulate evolution and de tection of the speciation via hybridization and polyploidization. But this region may not be useful for resolving phylogenetic relationships among families or taxa of higher hierarchy ow- ing to the rapid variation of the ITS sequences.

Key words: ITS sequence, Phylogenetics, Evolution, Angiosperm