Phylogenetic relationships and biogeographic patterns in North American members of Carex section Acrocystis (Cyperaceae) using nrDNA ITS and ETS sequence data

Carex section Acrocystis currently includes 27 taxa in North America. Recent phylogenetic studies have suggested that the North American and some but not all of the Eurasian species form a clade. Relationships and biogeographic patterns among species in this core-Acrocystis group are explored here using nuclear ribosomal (nrDNA) internal transcribed spacer region (ITS) and nrDNA external transcribed spacer region (ETS) sequence data. While maximum parsimony analysis of the ITS and ETS data provides only a moderately resolved branching structure for species relationships within the coreAcrocystis clade, maximum likelihood analysis provides a more resolved hypothesis of relationships in the section. The core-Acrocystis clade consists of a grade of Eurasian and primarily western North American species, with a wellsupported clade of only eastern North American species nested within this grade. ITS and ETS types do not coalesce within many species or species complexes. Possible explanations for the noncoalescent nature of ITS and ETS copies in Acrocystis are explored, including lineage sorting, hybridization, and cryptic species.