RESUMO
Phylogenetic analysis of ribosomal DNA internal transcribed spacer sequences from 35 members of western American Portulacaceae plus seven Portulacaceae outgroups generally supports morphologically based interpretations of multiple intercontinental disjunctions. The data neither support nor refute monophyly of the western American group but strongly support a group comprising the western American taxa plus Phemeranthus, the only strictly American genus of the morphology-based eastern American/African group of Portulacaceae, along with the Australian genus Parakeelya. Support is strong for the monophyly of Calandrinia, Montiopsis, Lewisia, Claytonia, and Montia, along with a sister relationship of the last two. The data neither strongly support nor refute the morphologically based diagnosis of Cistanthe, but they strongly support a clade including the North American Cistanthe section Calyptridium and the South American Cistanthe sections Amarantoideae and Philippiamra. The internal transcribed spacer data fail to resolve the phylogenetic relationships among most of the western American lineages, suggesting either rapid radiation or, alternatively, erratic evolution of the internal transcribed spacer. The internal transcribed spacer and morphological evidence together suggest that in this group there have been 8-13 dispersal and colonization events across >2000 km (1 for every 15-26 extant species in this group). The internal transcribed spacer data document complex molecular evolutionary patterns, including strong substitution biases, among-site rate heterogeneity, positional bias for deamination-type substitutions, nonstationarity, and variable rates of insertion/deletion. Our phylogenetic conclusions, however, do not appear to be sensitive to these patterns.