Phylogenetic relationships within Cyeadaceae inferred from non-coding regions of chloroplast DNA.

The intrageneric relationships among 24 species of five Cycas sections based on the combined data of three non-coding regions of chloroplast DNA: trnS-trnG, psbM-trnD and trnL-trnF, were determined using Neighbor-joining, Maximum parsimony and Maximum likelihood methods. All three methods showed similar topology, which divided Cycas into several clades. The first clade consisted of two sections, Cycas and Indosinenses, while the other clades contained Asiorientales, Wadeanae and Stangerioides, which could not be resolved. This result indicated the polyphyletic group of Cycas sections. Base substitution patterns further revealed that the subsection Rumphiae of the section Cycas could be separated into two groups (C. rumphii and C. edentata). In addition, the high bootstrap demonstrated that C. taitungensis was closely related to C. revotuta, while two other species of the section Wadeanae (C. wadei and C. curranii) were closely related, which agreed with the morphology. Data analyses suggested that the trnS-trnG sequences were more informative than the psbM-trnD and trnL-trnF regions in addressing phylogeny. Short and moderate repeated sequences detected in this region also indicated the high rate of evolution in the Cycas species. The 14 bp tandem repeats identified in this study are the first to be reported on the non-coding chloroplast DNA of Cycas.