Biosystematics of Platanthera bifolia s.l. (Orchidaceae): inferences from analysis of Scandinavian population samples

Over the years, various authors have (sub)divided the Eurasian moth pollinated Platanthera bifolia into several taxa. Advanced studies using multivariate morphometric analysis and/or genetic fingerprinting have all included regions where the situation appears particularly complex. With the aim to resolve variation patterns in a region where the situation seems less complex, we analysed morphometric and AFLP data from 13 Scandinavian populations using a range of uni- and multivariate statistical methods. Variation was largely continuous, though with (individuals from) short-spurred and long-spurred populations, respectively, forming loose groups. Provided that successful pollinator shifts usually occur between moth species with small difference in proboscis length, this pattern is congruent with the hypothesis that spur length in P. bifolia s.l. has mainly evolved through pollinator shifts followed by selection in response to proboscis length of the prevailing local pollinator species. Acknowledging an important adaptive role of spur length, observing that spur length was among the main contributors to morphological variation, and noting this pattern to be congruent with both AFLP patterns and habitat requirements, we advocate the formal distinction between a short-spurred and a long-spurred taxon. Adopting the operational definitions of species, subspecies and variety provided in Flora Nordica, the two taxa should be recognized as P. bifolia var. bifolia and P. bifolia var. latissima, respectively. A key to the varieties is provided.