MOLECULAR SYSTEMATICS AND A REVISED TAXONOMY OF THE ONOCLEOID FERNS (DRYOPTERIDACEAE, ONOCLEEAE)

Nucleotide sequences of the chloroplast-encoded rbcL gene were determi ned for all five species of the onocleoid ferns (Dryopteridaceae tribe Onocleeae), including both varieties of Onoclea sensibilis, and for o utgroup member Blechnum glandulosum. Together with GenBank sequences o f three additional onocleoid accessions and four additional taxa repre senting the outgroup Blechnaceae, these were analyzed cladistically un der the optimality criteria of maximum parsimony and maximum likelihoo d. Maximum parsimony yielded a single most-parsimonious tree with the three accessions of Onoclea sensibilis var. sensibilis left as an unre solved trichotomy. Maximum likelihood yielded a single set of three op timal trees whose only topological variation was in the trivial positi oning of the three accessions of Onoclea sensibilis var. sensibilis re lative to each other. Thus tree topologies of the onocleoid ingroup un der 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 Matt euccia struthiopteris plus Onocleopsis hintonii, and the two varieties of Onoclea sensibilis are well differentiated from each other. Matteu ccia struthiopteris and Onocleopsis hintonii form the least strongly s upported clade. Levels of sequence divergence among onocleoid taxa are compared with values from other taxa, and morphological and chromosom al data used in previous, noncladistic studies of the onocleoids are r eevaluated 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 supp orted at least at varietal rank and possibly at the rank of species. M olecular and morphological data bearing on the circumscriptions of Mat teuccia and Onocleopsis are equivocal but perhaps most concordant with their continued recognition as monotypic genera.