Elucidating the origin of Woodsia scopulina subsp. laurentiana (Woodsiaceae) in the Great Lakes region, an integrated systematic approach

Abstract

Cliff ferns (Woodsia, Woodsiaceae) are a primarily circumboreal genus with approximately ten species occurring in North America. Within this group, hybridization and whole genome duplication (polyploidy) are common. In the Great Lakes region, one taxon of particular interest is the allotetraploid (4x) Woodsia scopulina subsp. laurentiana Windham. This study aims to examine the evolutionary origin and biogeographical history of the Laurentian Cliff Fern, W. scopulina subsp. laurentiana, in the Great Lakes region, using a combined systematic approach. First, I used a niche modeling approach to estimate the current and historical range of W. scopulina subsp. laurentiana and its putative progenitors (W. scopulina subsp. scopulina and W. scopulina subsp. appalachiana). Second, I amplified and sequenced three chloroplast genes (trnG–trnR intergenic spacer, atpA, rbcL) to build a robust, well-supported phylogenetic hypothesis for the W. scopulina complex, giving special consideration to the origin(s) of W. scopulina subsp. laurentiana. Finally, I integrated a subset of my newly-generated molecular sequences (trnG–trnR) for the W. scopulina complex, from the Great Lakes region and across North America, with previously published fossil and molecular data to estimate the timing of diversification. This study provides clear cytogenetic and phylogenetic evidence for the maternal progenitor of W. scopulina subsp. laurentiana, as well as well as preliminary phylogenetic evidence for the maternal origins of Woodsia × abbeae in the Great Lakes region.