What does population structure analysis reveal about the Pterostylis longifolia complex (Orchidaceae)?

Abstract

Morphologically similar groups of species are common and pose significant challenges for taxonomists. Differences in approaches to classifying unique species can result in some species being overlooked, whereas others are wrongly conserved. The genetic diversity and population structure of the Pterostylis longifolia complex (Orchidaceae) in Tasmania was investigated to determine if four species, and potential hybrids, could be distinguished through genomic AFLP and chloroplast restriction-fragment-length polymorphism (RFLP) markers. Analysis of molecular variance (AMOVA) results indicated that little genetic variation was present among taxa, whereas PCoA analyses revealed genetic variation at a regional scale irrespective of taxa. Population genetic structure analyses identified three clusters that correspond to regional genetic and single taxon-specific phenotypic variation. The results from this study suggest that "longifolia" species have persisted throughout the last glacial maximum in Tasmania and that the complex may be best treated as a single taxon with several morphotypes. These results could have serious evolutionary and conservation implications as taxonomic changes could result in the instatement of a single, widespread taxon in which rarer morphotypes are not protected.