The internal transcribed spacer (ITS) region of the nuclear ribosomal DNA was sequenced from 21 accessions of Viguiera from South America, including 14 from Brazil. Overall there was only a small amount of sequence variation, less than 3.4% among South American samples and less than 4.5% between the South American samples and the Mexican V. flava. Phylogenetic analysis revealed little divergence among the Brazilian samples of Viguiera. The low level of ITS sequence variation was in striking contrast to the taxonomic diversity and chemical variability that have been reported for Viguiera in Brazil. The low level of sequence variation suggests that, despite its clear morphological and phytochemical adaptations to the cerrado, Viguiera is probably a relatively recent addition (less than 3 million years) to the flora of this area.