The phylogeny and taxonomy of onocleoid ferns (Dryopteridaceae tribe Onocleeae) inferred from rbcL nucleotide sequences

Three genera of onocleoid ferns have traditionally been recognized (Matteuccia, Onocleopsis, and Onoclea), but some recent studies subsume Onocleopsis into Matteuccia and transfer Asiatic species of Matteuccia to Onoclea. Although the 1995 analysis of fern phylogeny based on rbcL sequences showed that Matteuccia struthiopteris and Onoclea sensibilis constitute one clade of a polyphyletic Dryopteridaceae and that this clade is sister to Blechnaceae, it did not resolve conflicting views of generic circumscription within onocleoids. Sequences of rbcL from all five onocleoid species, including both varieties of Onoclea sensibilis, and from five outgroup species of Blechnaceae 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 these same three accessions of var. sensibilis relative to each other. Matteuccia orientalis and M. intermedia formed the basalmost ingroup clade strongly separated from the remaining taxa and sister to them, suggesting that they should be recognized in their own genus Pentarhizidium. 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, warranting varietal or possibly specific recognition. Molecular and other data bearing on the generic status of Matteuccia struthiopteris and Onocleopsis hintonii (which form the least strongly supported clade) are equivocal but perhaps most concordant with their continued recognition as monotypic genera.