The findings of a phylogenetic study of the genus Equisetum using both chloroplast and nuclear DNA sequences are presented and discussed. Analyses of chloroplast rps4 sequences indicate three distinct clades within the genus: (1) "traditional" subgenus Equisetum minus E. bogotense, (2) subgenus Hippochaete, and (3) E. bogotense. These rps4-based findings are consistent with inferences of a previous study (by Des Marais et al.) that used (chloroplast) rbcL and trnL-F sequences. We also amplified an (nuclear) ITS (ribosomal RNA internal transcribed spacer) region. We found a consistent PCR product size different between the two subgenera; E. bogotense shared the subgenus Equisetum haplotype. However, because of alignment difficulties and lower resolution, the ITS data are not incongruent with the "three clade" hypothesis based on chloroplast DNA data.

Key words: Equisetum, ITS, phylogeny., rps4