Molecular systematics of Carex section Ovales (Cyperaceae)

Phylogenetic relationships were studied at four levels among the predominantly New World sedges of Carex section Ovales (Cyperaceae): (1) among sections of subgenus Vignea, which contains section Ovales; (2) among major groups of section Ovales; (3) among the species of eastern North American clade I (ENA I); and (4) among accessions from several populations of each of three species of the eastern North American Carex tenera complex. Sequence data from chloroplast (trnL --trnF) and nuclear ribosomal DNA (the internal and external transcribed spacer regions, ITS and ETS) are largely congruent within section Ovales but strongly incongruent between other sections of the subgenus. Section Ovales is monophyletic with the exclusion of Carex illota. Incongruence between ITS and ETS data in placement of the Latin American C. bolanderi complex along with very high haploid chromosome counts in C. bolanderi suggest a possible allopolyploid origin for the progenitor of the complex. A very high chromosome count reconstructed at the base of section Ovales suggests that fission plays a role in chromosomal evolution within the genus. Eastern North America is ruled out as the ancestral area for section Ovales.;AFLP data provide strong phylogenetic signal within complexes of three to six species within ENA I, but they become uninformative at only slightly higher phylogenetic levels. A maximum likelihood method designed for analysis of restriction site data is used to evaluate the strength of support for alternative topologies. While there is little support for the precise placement of the root, likelihood of topologies in which any of the four clades identified within ENA I is forced to be paraphyletic is much lower than likelihood of the optimal tree. Parsimony reconstruction of ancestral character states on the AFLP topology suggest that (1) Heilborn's classic hypothesis that more highly derived species in Carex have higher chromosome counts does not apply within section Ovales, (2) the migration to Eastern North America involved a decrease in average chromosome count within section Ovales, and (3) intermediate chromosome counts are ancestral within ENA Clade I.