Molecular systematics and a revised taxonomy of the onocleoid ferns (Dryopteridaceae: Onocleeae)

Nucleotide sequences of the chloroplast-encoded rbcL gene were determined for all five species of the onocleoid ferns (Dryopteridaceae tribe Onocleeae), including both varieties of Onoclea sensibilis, and for outgroup member Blechnum glandulosum. Together with GenBank sequences of three additional onocleoid accessions and four additional taxa representing the outgroup Blechnaceae, these were analyzed cladistically under the optimality criteria of maximum parsimony and maximum likelihood. Maximum parsimony yielded a single most-parsimonious tree with the three accessions of Onoclea sensibilis var. sensibilis left as an unresolved trichotomy. Maximum likelihood yielded a single set of three optimal trees whose only topological variation was in the trivial positioning of the three accessions of Onoclea sensibilis var. sensibilis relative to each other. Thus tree topologies of the onocleoid ingroup under maximum parsimony and maximum likelihood were completely congruent. Matteuccia orientalis and M. intermedia formed the basalmost ingroup clade strongly separated from the remaining taxa and sister to them. Onoclea sensibilis is strongly separated from its sister clade of Matteuccia struthiopteris plus Onocleopsis hintonii, and the two varieties of Onoclea sensibilis are well differentiated from each other. Matteuccia struthiopteris and Onocleopsis hintonii form the least strongly supported clade. Levels of sequence divergence among onocleoid taxa are compared with values from other taxa, and morphological and chromosomal data used in previous, noncladistic studies of the onocleoids are reevaluated in light of this rbcL phylogeny. Matteuccia orientalis and M. intermedia should be recognized in their own genus Pentarhizidium, and the previously recognized varieties of Onoclea sensibilis are supported at least at varietal rank and possibly at the rank of species. Molecular and morphological data bearing on the circumscriptions of Matteuccia and Onocleopsis are equivocal but perhaps most concordant with their continued recognition as monotypic genera.