Molecular phylogenetics of 'Oreobolus' (Cyperaceae) and the origin and diversification of the American species

Abstract

Nuclear ribosomal DNA Internal Transcribed Spacer (ITS) and plastid 'trnL' intron and 'trnL-F' intergenic spacer regions were sequenced for 14 species of 'Oreobolus' (Cyperaceae) from throughout most of its distribution range (South America, Australasia, and Hawai'i), with the exception of the Malesian species; 'Costularia laxa' was used as outgroup. Phylogenetic trees were produced for ITS and 'trnL-F' datasets using maximum parsimony and maximum likelihood. We estimated species divergence times by enforcing a molecular clock on the Maximum Likelihood ITS tree, using the appearance of 'O. furcatus' in Hawai'i, no earlier than 5.1 mya, as a calibration point. Our results support the monophyly of the South American species with the southern 'O. obtusangulus' as sister to the rest. This South American clade is sister to the Australian 'O. pumilio', and the Australasian and Hawaiian species sampled form a basal grade. 'Oreobolus oligocephalus' is embedded within 'Oreobolus', rejecting its separation in the monotypic genus 'Schoenoides'. The transformed branch lengths of the ITS tree indicate a recent (5.5-6 mya) origin of the South American clade, followed by a northward migration and diversification of species along the Andes.