Splitting or synonymizing – genus concept and taxonomy exemplified by the Parmeliaceae in the Nordic region.
The current use of a 30 million year dateline for accepting genera in the Parmeliaceae is evaluated. Its value is doubtful since evolution obviously went quicker in some lichen groups compared with others. Parallel evolution is also very common among lichens. Polyphyletic genera should always be split, while sister groups may remain split or be combined after considering non-molecular characters.