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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 …