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Driscoll, Heather

Botany

2006

MS

Polystichum (Dryopteridaceae), one of the ten largest fern genera with more than 250 species worldwide, is a temperate and tropical genus that grows in montane regions throughout its range. A genus-wide molecular phylogeny for Polystichum and allied genera was reconstructed based on two chloroplast DNA sequences--rbcL and the trnL-F spacer-- from a taxonomically and geographically diverse sample to address the biogeographic origin and evolution of the three Hawaiian Polystichum species, all endemic to the Hawaiian Islands. Parsimony and Bayesian phylogenetic analyses of the combined data support a monophyletic Polystichurn and corroborate recent hypotheses as to membership and sequence of origin of the major groups within the genus. The Hawaiian Polystichum species are found to be polyphyletic; two separate lineages appear to have arrived independently from the Old World. The provenance of the diploid species Polystichum hillebrandii is eastern Asia, while the source region of the polyploid lineage comprising tetraploid P. haleakalense and octoploid P. bonseyi is likely, but not certainly, Asia. Our results demonstrate that the origin of the Hawaiian species of Polystichum parallel that of most Hawaiian fern groups, especially for members of large genera, in that multiple migrations are responsible for the observed diversity in the Hawaiian Archipelago.