Chloroplast 16S rDNA sequences and phylogenetic relationships of fern allies and ferns

Chloroplast 16S rDNA sequences from the charophyte algae Spirogyra and Coleochaete; the bryophytes Marchantia and Sphagnum; the fern allies Equisetum, Isoetes, Selaginella, Lycopodium, Tmesipteris and Psilotum; the eusporangiate ferns Angiopteris, Botrychium, and Ophioglossum; the leptosporangiate ferns Lydogium and Doodia; the gymnosperms Ephedra and Juniperus; and six angiosperms (two monocots and four dicots) were analyzed with the parsimony algorithm PAUP to infer phylogenetic relationships. The charophytes were the designated outgroup and the bryophytes were at the base of the land plant clade. Relationships of most of the fern allies and Angiopteris were unresolved but a clade containing Psilotum + Tmesipteris (Psilotales) was sister to a clade composed of Botrychium and Ophioglossum (Ophioglossales). A leptosporangiate fern clade was strongly supported, and this clade grouped weakly with Angiopteris. The Selaginella 16S rDNA sequence is apparently changing at a faster rate than the other sequences as evidenced by the extremely long branch associated with Selaginella. The effect of this long branch on the overall tree topology was tested by removing Selaginella from a subsequent analysis. Trees produced without Selaginella weakly supported the placement of Lycopodium at the base of the vascular plants clads but Isoetes grouped weakly with the seed plants. Removal of Selaginella also resulted in higher bootstrap values and decay indices for the majority of the clades.