Isoenzymatic and morphological data sets support the idea of the hybrid nature (probably F1 generation) of the semi-deciduous trees found. Nothofagus antarctica and N. dombeyi are probably more closely related than previously assumed. The relevance of pollen type in revealing evolutionary relationships between Nothofagus species is supported, and that of leaf-shedding pattern is rejected.

Diversity and dierentiation among 11 Argentine populations of the South American southern beech, Nothofagus nervosa (Phil.) Dimitri & Milano, were studied using eight isozyme gene markers. Genetic diversity, observed heterozygosity, mean number of alleles per locus, Gregorius' genetic distance, amount of genetic dierentiation and mean level of dierentiation among populations were estimated. Introgression of N. obliqua into the gene pool of N. nervosa was analysed using two species-speci®c isozyme gene markers (Adh-A and Pgi-B). As in most forest tree species, the main genetic variation was found within populations. Mean observed heterozygosity for the species was 17.3%, whilst mean level of genetic dierentiation (d ge ) was 4.6%. The most dierentiated locus was Mdh-B with dierences in 10% of the eective number of genes. From the analysis of the species distribution pattern it is suggested that genetic variation is geographically structured through the dierent lake watersheds along which the species is distributed. The occurrence of natural interspeci®c hybridization in some of the watersheds, together with the unidirectional gene¯ow along these watersheds sharpens this latitudinal structure. Dierent evolutionary stages in the introgressive hybridization process are apparently taking place in dierent lake watersheds.

Using next-generation sequencing, we developed the first whole-genome resources for two hybridizing Nothofagus species of the Patagonian forests that crucially lack genomic data, despite their ecological and industrial value. A de novo assembly strategy combining base quality control and optimization of the putative chloroplast gene map yielded ~32,000 contigs from 43% of the reads produced. With 12.5% of assembled reads, we covered ~96% of the chloroplast genome and ~70% of the mitochondrial gene content, providing functional and structural annotations for 112 and 52 genes, respectively. Functional annotation was possible on 15% of the contigs, with ~1750 potentially novel nuclear genes identified for Nothofagus species. We estimated that the new resources (13.41 Mb in total) included ~4000 gene regions representing ~6.5% of the expected genic partition of the genome, the remaining contigs potentially being nongenic DNA. A high-quality single nucleotide polymorphisms resource was developed by comparing various filtering methods, and preliminary results indicate a strong conservation of cpDNA genomes in contrast to numerous exclusive nuclear polymorphisms in both species. Finally, we characterized 2274 potential simple sequence repeat (SSR) loci, designed primers for 769 of them and validated nine of 29 loci in 42 individuals per species. Nothofagus obliqua had more alleles (4.89) on average than N. nervosa (2.89), 8 SSRs were efficient to discriminate species, and three were successfully transferred in three other Nothofagus species. These resources will greatly help for future inferences of demographic, adaptive and hybridizing events in Nothofagus species, and for conserving and managing natural populations.