Phylogenetic Implications of a Unique 5.8S nrDNA Insertion in Cyperaceae

The purpose of this study was to assess the phylogenetic utility of a large insertion (3 bp) in the 5.8S gene of nuclear ribosomal DNA (nrDNA) in Cyperaceae and selected Juncaceae. This was done by reconstructing the character evolution of the insertion on a phylogeny derived from rbcL sequences. Results suggest that the insertion was gained once at the base of Cyperaceae followed by multiple losses in its most-derived taxa. Despite several homoplastic losses (CI ! 0.20), the pattern of insertion loss (RI ! 0.88), and base pair variation within the insertion were useful for defining sedge clades at various taxonomic levels. For example, whereas a loss of the insertion appeared to characterize a major terminal clade within Cyperaceae, both an insertion loss and sequence variation were consistent with infrageneric clades previously discovered in an ITS phylogeny of Eleocharis. The presence/ absence of the insertion also supported previous conclusions based on morphological and molecular data that tribe Scirpeae and Scirpus s.l. are polyphyletic. In the context of our current understanding of Cyperaceae relationships, evolutionary patterns related to this insertion provide additional support for groups defined in prior phylogenetic analyses. The present analysis also suggests that the controversial position of Oxychloe andina (Juncaceae) in previous rbcL analyses, as sister to Cyperaceae (Y12978) or as nested within Cyperaceae (U49222), is due to the fact that Y12978 is a Juncaceae/ Cyperaceae chimera, whereas U49222 is the sequence of a Cyperaceae contaminant. When U49222 is excluded from analyses and the Cyperaceae portion of Y12978 is removed, Juncaceae and Cyperaceae are monophyletic with Oxychloe positioned within a Juncaceae clade of single-flowered genera.