The phylogenetic position of Carex section Phyllostachys and its implications for phylogeny and subgeneric circumscription in Carex (Cyperaceae).

Wide speculation surrounds the origin and phylogenetic relationships of the most highly reduced sections in the genus Carex. In order to gain a better understanding of phylogeny in Carex, the relationship of the reduced sect. Phyllostachys to 12 putatively related sections, representing all four subgenera (Primocarex, Indocarex, Carex, Vignea), was inferred from sequences of the ITS (internal transcribed spacer) region of nrDNA. Phylogenetic reconstructions identified two main clades: (1) a "compound" clade composed of sections from subg. Indocarex, Primocarex, and a portion of subg. Carex, and (2) a "reduced" clade consisting of sections from subg. Carex (Phyllostachys) and Primocarex (Filifoliae and Firmiculmes). Subgenus Indocarex was paraphyletic within the "compound" clade supporting classifications that have merged it within a wider subg. Indocarex/Carex/Primocarex line. Subgenus Primocarex was polyphyletic. This result was consistent with theories that extreme reduction has occurred along several different evolutionary lines in Carex. Phylogenetic theories inferred from the presence or abnormal growth of the rachilla were not supported by tree topologies. Difficult sectional circumscriptions, such as the separation of sections Laxiflorae and Careyanae, were strongly upheld by sequence data. The ITS region is an effective tool for defining sectional limits and for estimating relationships among sections in Carex, but does not provide enough phylogenetic information to fully resolve relationships below the sectional level.