Postglacial history and current population genetic diversity of a central-European forest plant Hacquetia epipactis

In the last decade, phylogeographical investigations have significantly contributed to our knowledge of the Quaternary history of several European species of trees in building forest ecosystems. In contrast, the phylogeography of mid- or low-altitude woodland understorey species that grow in moist and shaded forest habitats is still poorly understood. Here we focus on Hacquetia epipactis, a rare forest component of various types of deciduous forest communities, associated with Fagus sylvatica. We studied the genetic structure of populations of H. epipactis employing two molecular marker systems (AFLP fingerprinting and sequencing of several non-coding chloroplast DNA regions) to investigate the relationships among disjunctive groups of populations spanning its entire distribution in Europe (Dinaric Alps, Alps, Carpathians and adjacent Polish lowlands). The main goal of the present study was to explore the phylogeography and identify potential refugia and probable history of the development of the postglacial range of H. epipactis. We attempt to discuss this case study in the context of postglacial migration of forest forming species, especially beech, and postglacial assembly or co-migration of elements of forest communities. The non-coding chloroplast DNA showed a complete lack of genetic differentiation among populations, which may indicate a fast postglacial colonization from a single refugial area. AFLP data show no clear phylogeographical differentiation and indicate close relationships of the Dinaric and Carpathian/Moravian populations with a likely recent origin of the north-easternmost edge populations in Poland accompanied by a strong founder effect. Based on all the evidence, the most plausible scenario is a rapid, postglacial northward expansion from a Dinaric refugium, which concurs with the published postglacial scenario for beech. However, existence of a local refugium in the northern part of the present range is not excluded based on the distribution of genetic groups, which is also in congruence with the hypothetical last glacial history of beech. This suggests a possible shared migration history and role of Fagus expansion as the dominant species for the parallel establishment of Illyricoid species co-occurring in various beech-dominated communities. Limited gene flow among extant populations, due to disjunction and isolation at different spatial scales, is confirmed by significant correlation of genetic (pairwise Fst) and geographical distances.