Hybridization between species is common in plants, and plant hybrids are often partially fertile. Repeated backcrossing with the parents may result in introgression - transfer of genes between species. Thus, hybridization is one of the major avenues for adaptation and evolutionary change in plants. Plants are also well known for the process of allopolyploid speciation, by which hybridization is followed by an increase in chromosome number to produce a new species reproductively isolated from its progenitor species, but which combines characters and adaptive traits inherited from its parents. Nearly all plant species that are restricted to Scandinavia (endemics) are such allopolyploids. We use molecular markers to trace and describe hybridization and allopolyploid speciation. Hybridization results in reticulate evolution, and in our research we also try to understand the evolutionary consequences of this process.