A phylogenetic study of Saxifraga sect. Saxifraga (Saxifragaceae) based on nrDNA ITS sequences

Parsimony analyses of 54 nrDNA ITS (Internal Transcribed Spacer) sequences of Saxifraga sect. Saxifraga were performed. In addition to some unresolved clades, there is strong disagreement between the ITS phylogeny and previous classifications based primarily on morphology. The extensive cytological instability of sect. Saxifraga prevents previous cytotaxonomical results from resolving the incongruence between molecular and morphological data. Dissimilar topologies between chloroplast (matK) and nuclear (ITS) trees for eight species of sect. Saxifraga suggest that gene trees and the true species tree are not coincident. Recent and mid-term reticulation is proposed as an explanation for the incongruence between morphological, cytological, organellar, and nuclear data. Homogenization in multigene families, such as the ITS region, via concerted evolution may be the key to the interpretation of results based on ITS sequences within sect. Saxifraga. The use of organellar genes in a larger sample should help to determine whether extensive reticulation occurs in sect. Saxifraga, as has been documented in various genera of Saxifragaceae.