Phylogenetic considerations below the sectional level in Carex

Abstract

Few estimates of phylogenetic relationship below the sectional level have been proposed within the genus Carex (Cyperaceae). The reasons for this include (1) poorly circumscribed sections (paraphyletic and polyphyletic), (2) uncertain relationships among sections, and (3) difficulty in objectively assessing character state polarities. The operational difficulties posed by points 2 and 3 can be overcome through the use of character compatibility analysis, if it can be demonstrated that the section under study is monophyletic (point 1). This technique enables the investigator to generate hypotheses of relationship while minimizing the number of prior assumptions. Hypotheses of phylogenetic relationship are presented for the taxa within Carex sections Phyllostachyae, Limosae, and Ceratocystis. The topologies of these unrooted networks are assessed using external data sets (chromosome numbers, etc.) that serve as tests of the hypotheses, and may allow for a posteriori determination of character state polarities. In sections Ceratocystis and Limosae, these analyses provide strong support for the notion that chromosome evolution in Carex proceeds in a linear stepwise fashion. The results for section Phyllostachyae contradict this notion. Synthesis of all available data, coupled with phylogenetic reconstruction, will enable caricologists to provide more convincing arguments about the nature, direction, and factors influencing character state change.