| Summary: | ITS1 rRNA sequences from 19 Equisetum specimens representing 9 recognized species and 3 hybrid taxa were compared in this study. Most sequences had comparable lengths of 231 to 232 bases However, the sequence for E. sylvaticum had a 62-base deletion, making it only 170 bases in length. RNA secondary structures for internal transcribed spacer 1 (ITS1) were predicted and evaluated. For each sequence, 4 sequence motif regions were identified, folded individually, and concatenated for the final overall secondary structural prediction. One sequence motif region (designated as Motif 3) displayed statistically significant (p=0.003) secondary structural variation that distinguished specimens of subg. Hippochaete and subg. Equisetum. However, structural variation did not tend to unite conspecific specimens, nor did it consistently distinguish among different species. Phylogenetic analyses of complete ITS1 sequences were also performed, which clearly grouped specimens according to subgenus. However, different specimens representing the same species were not always joined in the same clade. Possible causes for this observation may include geographically based variation or possible hybridization between species of the same subgenus. ITS1 nucleotide sequence data as well the secondary structure obtained for the sequence Motif 3 appear to be useful for delineating Equisetum specimens on a subgeneric basis but may not be as suitable for resolving relationships within and between species.
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