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Climatic oscillations during the Quaternary strongly affected the distribution of warm-temperate tree species, which experienced local restrictions into ice-free areas and posterior expansions. To evaluate the impact of these range movements on the genetic structure of populations, we performed a phylogeographical analysis of the species Nothofagus obliqua with chloroplast DNA markers. A total of 27 populations covering the whole natural distribution range were analyzed using polymerase chain reaction-restriction fragment length polymorphism. Diversity (h T , h S ), allelic richness (r g ), and differentiation among populations for unordered (G ST ) and ordered alleles (N ST ) were calculated. The relationships among haplotypes were evaluated by the construction of a minimum spanning network. The spatial distribution of the genetic variation was analyzed through a Mantel test and with a nested analysis of molecular variance to differentiate between geographic regions. The screening of 11 non-coding regions allowed the identification of 14 haplotypes. A high genetic differentiation was detected (N ST =0.875 and G ST = 0.824) with the existence of phylogeographic structure (p< 0.05). The distribution of the genetic variation was partially explained by the topography of the region when the populations were divided longitudinally into Coastal Mountains, Central Valley, and Andes Mountains ( RT = 0.093, p=0.001). In agreement with pollen records, our results support the hypothesis of Coastal refuges since the region harbors high diversity together with older and private haplotypes. Long-lasting persistence of some Coastal populations without contribution to recolonization is proposed. Additional refuges are also postulated along the Andes and Longitudinal Valley. Survival in multiple glacial refuges is discussed together with the possible migratory routes.

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Aim  The distribution of the genetic variation in long‐lived species is a combination of both, historical and current processes. In Nothofagus nervosa (Phil.) Dim. et Mil., the possible existence of multiple glacial refugia, the unidirectional gene flow along fragmented areas and the natural hybridization with the related species Nothofagus obliqua (Mirb.) Oerst. highlights as the most important factors responsible for modelling its genetic structure. The present study aims to find out the relative importance of these evolutionary processes in determining the distribution pattern of the genetic variation in N. nervosa. Location  The study was carried out in north‐western Patagonia, Argentina. Twenty populations covering the entire distribution range of N. nervosa in Argentina were analysed. For comparison purposes, three populations from Chile were also included. Methods  Genetic variation was detected using isozyme gene markers; diversity and differentiation parameters were calculated. A cluster analysis was performed and the correlation between genetic and geographical distances was tested. Results  Levels of genetic variation were relatively high given the small distribution range of the species in Argentina. Genetic and geographical distances were not correlated and a longitudinal trend in the genetic variation was evident. Hotspots of diversity with rare and private alleles were observed among western populations, while hybrid seeds were found almost exclusively among eastern populations. Main conclusions  The higher level of diversity observed in western populations could be related with the location of glacial refugia. Furthermore, it should also reflect low levels of gene flow given the eastward unidirectional winds. On the contrary, ancient and current interspecific hybridization processes would mainly cause the particular genetic constitution of the eastern populations. Evidence is presented supporting that glaciations and hybridization were the main factors shaping the distribution of the genetic variation in N. nervosa.