RIBOSOMAL AND CHLOROPLAST DNA EVIDENCE FOR DIVERSIFICATION OF WESTERN AMERICAN PORTULACACEAE IN THE ANDEAN REGION

Resumo

Sequences of the ribosomal DNA internal transcribed spacer (ITS) region and the chloroplast DNA ycf3-trnS intergenic
spacer were determined for 183 samples representing Chilean and non-Chilean taxa of western American Portulacaceae
and their outgroups. The data refine previous inferences of generic circumscriptions and interrelations. In particular, the
data reveal that an earlier circumscription of Cistanthe Spach is polyphyletic and also reveal a North American clade
comprising Claytonia L., Lewisia Pursh, Lewisiopsis R. Govaerts, and Montia L. Within the South American genera, two
patterns emerge from the data: (1) in some cases, interspecific divergence is remarkably low given the markers employed
and estimated number of species; and (2) where divergence of one or both markers offer phylogenetic resolution, there is
conflict between them and/or with morphology. The patterns can be evaluated in terms of two phenomena: (1)
morphological/ecological radiation proceeding much faster than sequence divergence; and (2) frequent hybridization. In
the latter case, the gene tree patterns may distort the true timing and cladistic pattern of morphological and ecological
diversification. At present, the degree to which evidence for hybridization among the Chilean Portulacaceae will prove to
be the rule or the exception is unclear. Nonetheless, spatial and temporal ecological patterns in Chile generally favor
hybrid formation and persistence.