All members of the C. dryophila complex have a heterothallic tetrapolar mating system. Several intercompatible groups are broadly distributed over several continents including North America, Europe and Asia. Limitations of the biological species concept are discussed, and a phylogenetic based species concept is proposed, which provides information about evolutionary relationships among allopatric mating groups based on combined data from mating compatibility, morphology and macromolecules. -from Author