XVI International Botanical Congess

Hierarchical structure is found in a nrDNA ITS data set from Armeria regardless of the likely occurrence of extensive gene flow combined with biased concerted evolution. This implies that an informative data set may be produced despite, or thanks to, the erasure of phylogenetic histories at the specific level caused by two such conflicting forces. The resulting pattern is tightly linked with geography and does not respect taxonomic specific boundaries. Arguments in support of this striking possibility are outlined, including (1) geog raphic structure of the ITS data set superimposed to taxonomic boundaries, (2) active and biased homogenization of ITS sequences detected in artificial F2 hybrids, (3) the placement of artificial hybrids in cladograms when added to the ITS data set, (4) the previous non-molecular evidence supporting the occurrence of gene flow.