The origin and phylogenetic position of Carex section Phyllostachys in the genus Carex, Cyperaceae

Abstract

Carex section Phyllostachys is a small, highly reduced section of eight species confined to North America, north of Mexico. Although the section is easily circumscribed, its unusual appearance has led to wide speculation concerning its origin and phylogenetic position in Carex. In order to gain a better understanding of phylogeny in this complex genus, anatomical, micromorphological, macromorphological, and molecular DNA characters were used to clarify the phylogenetic position of sect. Phyllostachys in Carex, and to determine the relationships of its species. The taxonomic utility of anatomical, micromorphological, and molecular characters, for species and sectional circumscriptions, was also assessed. A cladistic analysis using anatomical, morphological, and ITS sequence data suggests that section Phyllostachys can be divided into two distinct clades: (1) a "wide-scaled" clade consisting of Carex backii, C. saximontana, and C. latebracteata; and (2) a "narrow-scaled" cla e consisting of C. willdenowii, C.superata, C. basiantha, C. juniperorum, and C. jamesii. Trends in character evolution and flower number appear to be related to breeding systems although this is not supported by previous studies utilizing isozymes. Correlations between phytogeography, glacial movements, and phylogeny suggest that speciation in the section may have been influenced by the events of the Pleistocene. Estimates of divergence times based on the mutation rate of the ITS region in the genus Dendroseris, indicate that most of the speciation in the section has occurred within the last 1.7 my. (Abstract shortened by UMI.)