Abstract: Partial sequences of chalcone synthase (CHS) gene exon 2 were amplified by PCR method from genomic DNA of 10 species of the basal eudicots. After cloning and sequencing , 26 seqences were obtained . There were two to four copies of CHS gene family among various plants. All of sequences showed a similarity higher than 70% at the nucleotide level . A 29-base deletion was found in a copy (CedeCHS3) in Ceratophyllum demersum, which indicated that the function of the CHS enzyme in this species was lost. GrroCHS8, a copy from Grevillea robusta, had many mutations at active sites, implying the new function may be devoloped in this copy. The result of analyzing the base content revealed that only the sequences from Buxus bobinieri have GC bias, especially at the third base of codes, and the GC content is more than 70%. All of molecular phylogenetic trees, based on the Beyesian, MP, and NJ methods, consisted of three major clades. Four sequences from Ceratophyllum demersum were grouped into a monophyletic clade (subfamily Ⅱ ). Two sequences out of Trochodendron aralioides nested in subfamily Ⅲ. Another three sequences from Kingdonia uniflora interspersed among different subclades of subfamily Ⅰ. Sequences of most species dispersed in subfamily Ⅰ and subfamily Ⅲ. And it revealed that CHS gene family derived from two ancestor copies, which had existed before eudicots were evolved. The two copies experienced different evolutionary process among different species . These differences related to the diversity of habits and environments of these plants.

Key words: Basal eudicots