LITTLE, DAMON P. AND DAVID S. BARRINGTON.* L.H. Bailey Hortorium, Cornell University, Ithaca, NY 14853 and Department of Botany & Agricultural Biochemistry, University of Vermont, Burlington, VT 05405. - Major evolutionary events in the origin and diversification of the fern genus Polystichum (Dryopteridaceae).
The family Dryopteridaceae includes some of the most species-rich
genera in the ferns, including Athyrium, Dryopteris,
and Polystichum–the subject of this inquiry. In this work we
identified the divergence events leading up to the origin of
Polystichum and discerned the major lineages within this large
genus. Our approach was to use molecular data from the chloroplast
gene rbcL to infer the phylogenetic history of selected
species of Polystichum and its traditional allies. We sampled
23 Polystichum species representing at least 11 of the 22
described sections and 10 species from allied genera. The
Polystichum species came from seven of the eight world centers
of diversity for the genus. Ten additional rbcL sequences
came from Genbank. We found support for a monophyletic narrowly
defined Polystichum, excluding a group of Asian species, P.
tripteron, P. deltodon, and P. lepidocaulon. All
species of Polystichum can be included in a monophyletic genus
Polystichum sensu lato if Cyrtomium is included in the
larger genus. The sister group of Polystichum sensu lato is a
tropical American group including Phanerophlebia and
Polystichopsis. At the limits of our immediate inquiry we
found a trichotomy leading to 1) a monophyletic group including all
the aforementioned taxa, 2) Dryopteris plus
Arachniodes, and 3) the single New-World Ctenitis
included in the sample. We found that Rumohra and
Didymochlaena were both remote from Polystichum in our
analysis. Within the genus, the taxa sampled from a continent often
constitute a monophyletic group, most notably those from Africa and
tropical America. We intend to pursue the more recent phylogenetic
history of the genus by addressing diversification within continents
using the intergenic spacer between rbcL and atpb.
Key words: Dryopteridaceae,phylogeny,Polystichum