Molecular evidence for allopolyploid speciation and recurrent origins in Platanthera huronensis (Orchidaceae)

The origin of the polyploid orchid Platanthera huronensis was inferred from variation at 305 intersimple sequence repeat (ISSR) and RAPD loci and cpDNA RFLP patterns generated from amplification and digestion of two noncoding regions, rpl16 intron and trnT-trnF region. Morphological intermediacy indicates that P. huronensis is likely an allopolyploid derivative of Platanthera dilatata and Platanthera aquilonis, and this hypothesis is supported by the data presented in this study. Nearly all of the bands found in P. huronensis were also identified in P. dilatata and/or P. aquilonis, to the exclusion of the other putative parental species examined. Nevertheless, phenotypic patterns of ISSR and RAPD bands were not strictly additive in P. huronensis, which reflects evolutionary divergence since initial formation of polyploid lineages or origin from parental populations that were not sampled. An analysis of cpDNA RFLP patterns revealed five unique haplotypes in P. huronensis and a high degree of geographic structuring. Western samples were more similar to P. dilatata while eastern samples were identical to P. aquilonis in cpDNA RFLP pattern. Collectively, these differences point to multiple independent origins and complex evolutionary histories in extant polyploid lineages. Because P. huronensis is morphologically and genetically distinct from other closely related species, its continued recognition at the rank of species is warranted.