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Dragon, Julie

Botany and Agricultural Biochemistry

2006

PhD

The genus Carex is one of the most widespread and ecologically important of all plant genera, yet the evolutionary and biogeographic history of most of its approximately 2,500 species remains unclear. Convergence and homoplasy have hindered elucidating phylogenetic relationships among taxa using traditional morphology. Dragon and Barrington (in press) identified a monophyletic group, the Carex aquatilis group, based on molecular data from nuclear spacers ITS and ETS. Phylogenetic analyses of nuclear ITS and ETS plus chloroplast psbA-trnH DNA sequences continue to support the monophyly of the highly diverse Carex aquatilis and C. lenticularis and their allies, the C. aquatilis group of section Phacocystis. Neither C. aquatilis nor C. lenticularis, however, are monophyletic as circumscribed. The sequence data could not resolve the relationships among the four varieties of C. aquatilis and their maritime allies from the C. subspathacea group. The western varieties of C. lenticularis are not sister to the eastern type variety. Three represent a morphologically diverse species, C. kelloggii, and exhibit little genetic variation from the most recent common ancestor of their clade. The other was found to be polyphyletic and comprises two species, the northern C. enanderi and C. plectocarpa from Montana. The C. aquatilis group now comprises 14 species: C. aquatilis, C. subspathacea, C. ramenskii, C. paleacea, and C. lyngbyei in C. aquatilis s. 1., and C. kelloggii, C. enanderi, C. hermannii, C. cuchumatanensis, C. lenticularis, C. decidua, C. rufina, C. eleusinoides, and C. plectocarpa. It is supported by molecular, morphological, and ecological data. Limited genetic variation within both C. aquatilis and C. kelloggii may be due to rapid radiation of each species. Biogeographic analyses indicate a mid-Pleistocene origin for the group around 0.88 mya from a North American ancestor. While an optimization of chromosome numbers on the phylogenetic tree indicates fission of chromosomes in most clades, an exception is the clade including C. eleusinoides and C. plectocarpa, where fusion is clearly indicated. A taxonomic treatment of the 14 species of the Carex aquatilis group is presented. Carex aquatilis and C. lenticularis are united by proximal involucral bract length, overall size, coloration, and spike size and shape, as well as amphistomatic and amphipapillose leaves, and diploid chromosome numbers from 68 to 92. I recognize a paraphyletic C. aquatilis s. s., with morphological and molecular support for a Eurasian clade of C. aquatilis, a North American clade of C. aquatilis var. substricta and var. minor, and a salt-tolerant clade of C. aquatilis var. dives. Carex kelloggii is also recognized as a paraphyletic species of three varieties: var. kelloggii, var. limnophila, and var. impressa.