The patterns of polyploid evolution in the Dactylorhiza majalis/elata/praetermis a complex (Western Europe) were assessed using evidence from nuclear ribosomal spacer (ITS) sequences. Individual diploids were first sequenced to determine variation within each of the putative parental complexes, and these were used to construct a phylogenetic assessment of these taxa. The allopolyploids were thought to have been formed by crosses between D. fuchsii and D. incarnata, but the majority of the majalis/elata complex exhibit one of the two D. fuchsii alleles (F1 and F2), except for D. majalis subsp. sphagnicola, which has the D. incarnata allele (I). None of the taxa of hybrid origin exhibits any evidence of two alleles, except for backcrosses onto D. incarnata, which are putatively triploid. Dactylorhiza maculata has usually been considered an autotetraploid derived from D. fuchsii, but all accessions examined so far have an allele (M) shared with other diploids, such as D. foliosa and D. iberica, which raises the possibility that D. maculata is not an autotetraploid but rather an allotetraploid derived from one of these taxa and D. fuchsii. Dactylorhiza praetermissa has often been considered a subspecies of D. majalis, but it has an ITS allele that so far is unknown in any diploid. We speculate that this allele may occur in one of the eastern diploids unsampled so far, such as D. euxina. Although subject to gene conversion and therefore not strictly biparentally inherited, ITS is nonetheless a useful marker to determine one of the parents of hybrid taxa. Further research is now underway to determine the direction of each of the crosses that produced the allotetraploids, and in particular to find markers to discriminate between the diploids with the M allele.

Key words: allopolyploidy, Dactylorhiza, hybridization, ITS, Orchidaceae